Tell a creationists that humans and chimpanzees have 98% of their genomes in common, and they'll tell you this doesn't prove common origins or 'macro-evolution', but show them evidence that two bacteria have evolved from a common ancestor because they have 80% of their genome in common and they'll tell you this doesn't mean they've evolved because they are both still 'bacteria kind'.
So, why doesn't 98% commonality mean humans and chimpanzees are both still 'ape kind'?
But the evidence that the two bacteria, Mycobacterium tuberculosis, and the newly-discovered M. spongiae is compelling, and gives a clue as to the origins of M. tuberculosis, one of the most deadly pathogenic bacteria, possibly from marine origins.
Bogdan Onac studies the phreatic overgrowths seen in this photo. They grow exactly at sea level and offer a more accurate reconstruction of past sea level history. He used these to determine the age of the submerged bridge.
Photo: M.À. Perelló
Close-up view of the submerged stone bridge from Genovesa Cave, Mallorca, Spain
The Spanish Balearic Island of Mallorca (Majorca), a favourite holiday destination for Brits looking for sun, sea and sand, is composed largely of limestone which lends itself to cave formation and limestone caves lend themselves to stalactite formation.
They also provided shelters for early humans, so the evidence of human presence gives us a good picture of the timing of human migration into the area.
Like 99,9975% of Earth's history, the events recorded in these Mallorcan caves happened in the long pre-'Creation Week' history, long before creationists believe Earth was made out of nothing by magic.
Readers may recall my recent blog post concerning what is known of the changes in biodiversity as the Mediterranean dried up, then flooded again about 5.5 million years ago due to plate tectonic movements. These Mallorcan caves formed after those catastrophic events but still well before creationism's 'Creation Week'.
The stalactites in one cave in particular, the Genovesa Cave at the eastern end of the island hold a record of sea-level changes that correlate with known periods of glaciation and interglacial warmer periods. During periods of glaciation, water was locked up in polar ice and glaciers, so sea-levels fell.
What information do you have on the Genovesa Cave in Mallorca, Spain, and what it tells us of sea-level changes?
Genovesa Cave, located on the eastern coast of Mallorca, Spain, is a notable site for studying past sea-level changes due to its unique speleothem formations (such as stalactites and stalagmites) and its position relative to current sea levels.
Key Information About Genovesa Cave
Geological Context:
Genovesa Cave is a partially submerged cave system found on the island of Mallorca, part of the Balearic Islands in the western Mediterranean Sea.
The cave has been naturally formed in limestone rock, a type of carbonate rock that is particularly responsive to changes in sea level.
Evidence of Past Sea-Level Changes:
Speleothem Growth Stages: The most significant evidence for past sea-level changes comes from speleothems, which are mineral deposits formed in caves by the precipitation of carbonate minerals from dripping water. When sea levels rise, the cave becomes submerged, and speleothem growth ceases due to a lack of contact with air. When sea levels fall, the cave is re-exposed to air, allowing speleothems to grow again.
Dating Techniques: Researchers use uranium-thorium (U-Th) dating methods to date these speleothems accurately. The growth and cessation periods can be correlated with known global sea-level fluctuations, such as those associated with glacial and interglacial cycles during the Quaternary period (the last 2.6 million years).
Sea-Level Highstands and Lowstands:
Studies of Genovesa Cave have identified speleothems that formed during several past interglacial periods when sea levels were higher than today. This provides evidence for higher sea levels during warm periods such as the Last Interglacial (about 125,000 years ago).
Conversely, periods when the cave was submerged or when speleothem growth was halted correspond to glacial periods when sea levels were much lower, sometimes up to 120 meters lower than the current level.
Implications for Understanding Sea-Level Changes
Local and Global Sea-Level Correlation:
The data obtained from Genovesa Cave speleothems align well with global records of sea-level changes, such as those derived from coral reefs and marine terraces. This reinforces the idea that the cave provides a reliable local record that reflects broader, global sea-level trends.
Understanding the Mediterranean Sea's Response:
The cave's findings contribute to our understanding of how the Mediterranean Sea responded to global climatic events. During periods of rapid deglaciation, for example, meltwater pulses could have caused rapid sea-level rises, which would be recorded in the cave's geological formations.
Insights into Future Sea-Level Rise:
Studying past sea levels helps scientists predict future changes, particularly in the context of global warming and potential ice sheet melting. The high-resolution records from Genovesa Cave can help refine models of future sea-level rise, especially in understanding how fast and how much sea levels could change.
In Summary
Genovesa Cave in Mallorca is a critical natural archive for studying past sea-level changes, providing both a local record of changes in the Mediterranean and contributing to the understanding of global sea-level fluctuations. The cave's speleothem formations, when dated, tell us about the timing and extent of past sea levels, helping us predict future changes.
Did the cave exist during the Messinian Salinity Crisis and the following Zanclean flood?
Genovesa Cave, like many other karstic cave systems on Mallorca, likely did not exist in its current form during the Messinian Salinity Crisis (MSC) and the subsequent Zanclean flood. However, understanding its formation requires a bit of geological context about these events and the development of the cave.
Geological Context of the Messinian Salinity Crisis and Zanclean Flood
Messinian Salinity Crisis (MSC) (5.96 to 5.33 million years ago):
The MSC was a period when the Mediterranean Sea was largely cut off from the Atlantic Ocean due to tectonic movements, leading to extreme evaporation and a significant drop in sea level. During this time, the Mediterranean became partially or fully desiccated, creating vast salt deposits and deep erosional features (like canyons and river systems) that extended below the current sea level.
Sea levels were drastically lower, estimated to have dropped by as much as 1,500 meters. The drop exposed large portions of the continental shelf and caused significant erosion of the landscape, including the areas around Mallorca.
Zanclean Flood (5.33 million years ago):
The Zanclean flood marked the end of the MSC, when the Strait of Gibraltar reopened, and Atlantic waters rapidly refilled the Mediterranean basin. This event is thought to have raised sea levels in the Mediterranean by up to 1,500 meters over a short period, flooding the previously exposed and desiccated areas.
Did Genovesa Cave Exist During These Events?
Formation of Genovesa Cave:
Genovesa Cave, like many karst caves, formed much later than the Messinian Salinity Crisis and the Zanclean flood. The formation of such caves typically occurs over long periods through the dissolution of limestone by slightly acidic groundwater. This process, known as karstification, is generally linked to periods when the sea level is relatively stable and when the water table is at an appropriate level to facilitate cave development.
Given that the MSC was a period of extreme environmental conditions (both in terms of erosion during the desiccation and rapid flooding during the Zanclean flood), the specific geological setting that would allow for the gradual formation of karstic caves like Genovesa likely did not exist until after these events.
Post-MSC Karst Development:
After the Mediterranean was refilled and the sea level stabilized following the Zanclean flood, conditions would have been more suitable for the formation of karst systems like Genovesa Cave. The Quaternary period, which began about 2.6 million years ago, saw multiple cycles of glacial and interglacial periods, during which fluctuations in sea levels, combined with periods of stability, promoted the development of karst caves in the limestone regions of Mallorca.
Timing of Cave Formation:
The specific timing of the formation of Genovesa Cave is not precisely known, but it is generally accepted that most of the karst caves in Mallorca formed during the Pleistocene epoch (2.6 million to 11,700 years ago) or even more recently. The cave's features and deposits suggest that it has undergone several phases of exposure and submersion due to sea-level changes throughout this period, well after the MSC and Zanclean flood.
Conclusion
Genovesa Cave, in its current form, did not exist during the Messinian Salinity Crisis or the subsequent Zanclean flood. The cave likely formed much later, during the Quaternary period, as conditions became suitable for karstification following the stabilization of Mediterranean sea levels after these dramatic geological events. The MSC and the Zanclean flood were important in shaping the broader landscape of the Mediterranean region, but the specific conditions necessary for the formation of caves like Genovesa developed much later.
What are phreatic overgrowths on Speleothems (POS)?
Phreatic overgrowths on speleothems (POS) are unique mineral deposits that form in coastal cave environments at the interface between freshwater and seawater. These overgrowths are specifically associated with periods when the cave is partially submerged in a mix of fresh and saline water, typically at or near sea level. They provide important clues about past sea-level positions and climate conditions.
Key Characteristics of Phreatic Overgrowths on Speleothems
Definition:
Phreatic overgrowths on speleothems are secondary carbonate deposits, typically composed of minerals like calcite or aragonite. They form on existing speleothems (such as stalactites, stalagmites, or flowstones) when the cave environment is inundated by a fluctuating water table that is influenced by sea level.
Formation Environment:
These overgrowths develop in the "phreatic zone" of caves— the zone that is below the water table and is saturated with water. In coastal caves, this zone is directly affected by sea-level changes. When sea level is stable or fluctuates within a certain range, the mixing zone between freshwater and saline water can lead to mineral precipitation on submerged speleothems.
Mechanism of Formation:
Phreatic overgrowths form due to a process known as "degassing" or "precipitation" when carbon dioxide (CO2) dissolved in water escapes into the cave air. This loss of CO2 from water that is saturated with calcium carbonate (CaCO3) promotes the deposition of calcite or aragonite on existing cave formations.
In coastal caves, the mixing of fresh and saltwater enhances this process. Freshwater entering the cave mixes with seawater, creating conditions where minerals precipitate more readily due to changes in water chemistry, such as shifts in pH, temperature, and CO2 concentration.
Morphology and Appearance:
Phreatic overgrowths typically form flat or gently sloping horizontal crusts, rims, or coatings on existing cave formations. Their horizontal nature reflects the stable water table level at which they formed.
These deposits can vary in thickness and are often found at multiple levels within the cave, corresponding to different sea levels over time.
Importance of Phreatic Overgrowths on Speleothems
Indicators of Past Sea Levels:
POS are valuable indicators of past sea levels because they form at specific elevations related to the water table, which in coastal environments is closely linked to sea level. By dating these formations using techniques such as uranium-thorium (U-Th) dating, scientists can reconstruct past sea-level positions and determine the timing and magnitude of sea-level changes over thousands to hundreds of thousands of years.
Understanding Paleoclimatic Conditions:
Beyond sea levels, POS can provide insights into broader paleoclimatic conditions. The chemical composition of these overgrowths (e.g., stable isotopes of oxygen and carbon) can offer information about past temperature, rainfall patterns, and even water source characteristics.
Calibrating Sea-Level Rise Models:
The precise dating of phreatic overgrowths helps in calibrating models of sea-level rise, particularly when cross-referenced with other geological and paleoclimatic data, such as coral reefs, marine terraces, and ice cores. This is particularly important for understanding the rate of sea-level rise in response to past climate events, such as glacial and interglacial periods.
Examples of POS Studies
Mediterranean Caves (Mallorca, Spain): In Mallorca, POS have been extensively studied in caves like Genovesa Cave and others along the coast. These formations have been used to map out the history of Mediterranean sea-level changes over the last several hundred thousand years, including periods such as the Last Interglacial (about 125,000 years ago).
Caribbean and Other Coastal Regions: Similar studies have been conducted in coastal caves in the Caribbean and other regions, where POS help reconstruct sea-level fluctuations and regional climate changes.
Summary
Phreatic overgrowths on speleothems are carbonate deposits formed in caves at the interface between freshwater and seawater, directly reflecting past sea levels. They serve as crucial archives for understanding past sea-level changes, climate conditions, and the complex interplay between global climate and regional environmental changes.
In the context of dating caves, what does the following mean?
'A 232Th/238U-234U/238U-230Th/238U (plotted as a Rosholt A type) isochron age of 5479 ± 120 years B.P.'
The phrase describes the result of a specific type of uranium-thorium dating method used to determine the age of materials, such as carbonate deposits in caves. Let's break down what each part of this phrase means:
Uranium-Thorium (U-Th) Dating Overview
Uranium-Thorium (U-Th) dating also known as Thorium-230 dating is a radiometric dating technique used to determine the age of calcium carbonate materials like speleothems (stalactites, stalagmites, and other cave formations). The method relies on the radioactive decay of uranium isotopes to thorium isotopes. Here's a breakdown of the isotopes involved:
238U (Uranium-238): The parent isotope, which decays over time into various intermediate daughter isotopes, including 234U (Uranium-234) and 230Th (Thorium-230).
232Th (Thorium-232): A stable, non-radioactive isotope of thorium that is not involved in the decay chain but can be present in the sample as a contaminant or from initial conditions.
Explanation of the Phrase
"232Th/238U-234U/238U-230Th/238U":
These ratios represent the proportions of different isotopes present in the sample.
232Th/238U: Indicates the ratio of thorium-232 to uranium-238 in the sample.
234U/238U: Indicates the ratio of uranium-234 (an intermediate decay product) to uranium-238.
230Th/238U: Indicates the ratio of thorium-230 (the target daughter isotope) to uranium-238.
"Plotted as a Rosholt A type isochron":
An isochron is a graphical method used to determine the age of a sample by plotting the ratios of isotopes against each other. The slope of the line (the isochron) represents the time that has passed since the sample's formation.
"Rosholt A type" refers to a specific type of isochron plot developed by John Rosholt, which plots the ratios of these isotopes in a way that accounts for initial thorium contamination (232Th). This method provides a more accurate age by correcting for the presence of any initial, non-radiogenic thorium in the sample.
"Isochron age of 5479 ± 120 years B.P.":
This is the calculated age of the sample, determined by the U-Th dating method using the isochron plot.
5479 years B.P.: This means "5479 years Before Present," where "Before Present" is typically defined as before the year 1950. The sample is estimated to have formed 5479 years ago.
± 120 years: This represents the margin of error or uncertainty in the dating. The true age is likely within the range of 5479 years plus or minus 120 years (i.e., between 5359 and 5599 years ago).
Summary
The phrase refers to a method of dating a cave sample using uranium-thorium dating and an isochron plot (Rosholt A type) to determine that the sample is approximately 5479 years old, with an uncertainty of ±120 years. The use of multiple isotope ratios and the isochron method helps correct for initial contamination and provides a more accurate age estimate.
This allowed stalactites to grow as water containing dissolved minerals seeped through the cave roof and dripped down, evaporating as it did so, and leaving a record of rainfall. During interglacial period, sea-levels rose, submerging the caves and preventing the growth of stalactites, leaving a record of these sea-level rises.
But, apart from these records of climate and sea-level changes, the Genovesa Cave contains a more tangible record - that of human habitation on the island and so of colonisation of the Western Mediterranean and the Iberian peninsula in particular.
It is a submerged stone bridge, built when the sea-levels were lower at the height of the last ice age. The bridge was used to cross a now submerged small lake at a low point in the cave system and must have been deliberately constructed.
Scientists these days rarely, if ever, set out to refute creationist mythology but all do so incidentally, simply by doing what good science does and discovering the facts, and this discovery, by speleogeologists from the University of South Florida, does just that. It is the subject of a recent open access paper in Communications Earth & Environment and a recent news release from the University of South Florida:
What a submerged ancient bridge discovered in a Spanish cave reveals about early human settlementA new study led by the University of South Florida has shed light on the human colonization of the western Mediterranean, revealing that humans settled there much earlier than previously believed. This research, detailed in a recent issue of the journal, Communications Earth & Environment, challenges long-held assumptions and narrows the gap between the settlement timelines of islands throughout the Mediterranean region.
Reconstructing early human colonization on Mediterranean islands is challenging due to limited archaeological evidence. By studying a 25-foot submerged bridge, an interdisciplinary research team – led by USF geology Professor Bogdan Onac – was able to provide compelling evidence of earlier human activity inside Genovesa Cave, located in the Spanish island of Mallorca.
The presence of this submerged bridge and other artifacts indicates a sophisticated level of activity, implying that early settlers recognized the cave's water resources and strategically built infrastructure to navigate it.
Professor Bogdan P. Onac, Lead author
Karst Research Group
School of Geosciences
University of South Florida, Tampa, FL, USA.
The cave, located near Mallorca’s coast, has passages now flooded due to rising sea levels, with distinct calcite encrustations forming during periods of high sea level. These formations, along with a light-colored band on the submerged bridge, serve as proxies for precisely tracking historical sea-level changes and dating the bridge's construction.
Mallorca, despite being the sixth largest island in the Mediterranean, was among the last to be colonized. Previous research suggested human presence as far back as 9,000 years, but inconsistencies and poor preservation of the radiocarbon dated material, such as nearby bones and pottery, led to doubts about these findings. Newer studies have used charcoal, ash and bones found on the island to create a timeline of human settlement about 4,400 years ago. This aligns the timeline of human presence with significant environmental events, such as the extinction of the goat-antelope genus Myotragus balearicus.
By analyzing overgrowths of minerals on the bridge and the elevation of a coloration band on the bridge, Onac and the team discovered the bridge was constructed nearly 6,000 years ago, more than two-thousand years older than the previous estimation – narrowing the timeline gap between eastern and western Mediterranean settlements.
This research underscores the importance of interdisciplinary collaboration in uncovering historical truths and advancing our understanding of human history.
Professor Bogdan P. Onac.
This study was supported by several National Science Foundation grants and involved extensive fieldwork, including underwater exploration and precise dating techniques. Onac will continue exploring cave systems, some of which have deposits that formed millions of years ago, so he can identify preindustrial sea levels and examine the impact of modern greenhouse warming on sea-level rise.
This research was done in collaboration with Harvard University, the University of New Mexico and the University of Balearic Islands.
Abstract
Reconstructing early human colonization of the Balearic Islands in the western Mediterranean is challenging due to limited archaeological evidence. Current understanding places human arrival ~4400 years ago. Here, U-series data from phreatic overgrowth on speleothems are combined with the discovery of a submerged bridge in Genovesa Cave that exhibits a distinctive coloration band near its top. The band is at the same depth as the phreatic overgrowth on speleothems (−1.1 meters), both of which indicate a sea-level stillstand between ~6000 and ~5400 years ago. Integrating the bridge depth with a high-resolution Holocene sea-level curve for Mallorca and the dated phreatic overgrowth on speleothems level constrains the construction of the bridge between ~6000 and ~5600 years ago. Subsequent sea-level rise flooded the archeological structure, ruling out later construction dates. This provides evidence for early human presence on the island dating at least 5600 and possibly beyond ~6000 years ago.
Introduction
Mallorca, the main island of the Balearic Archipelago, is the sixth largest in the Mediterranean Sea, yet it was among the last to be colonized1. An in-depth discussion concerning the earliest colonization of various Mediterranean islands, including Mallorca, may be found in Cherry and Leppard1, Dawson2, and Simmons3. Despite extensive research on this topic, there has been considerable disagreement about the timing of the earliest colonization of Mallorca. Radiocarbon dating of bone material excavated from Cova (Cave) de Moleta indicate human presence on the island as early as 7000 calibrated years before present (cal B.P.)4. Subsequent age determinations from findings in Cova de Canet, further extended the timeline, suggesting human occupation dating back to approximately 9000 cal B.P.5. A series of publications6,7,8,9,10,11 revealed inconsistencies regarding the exact stratigraphic position and context of the dated bone (sample KBN-640d12) in Cova de Moleta. Due to the overall poor preservation of the samples and the lack of clear and specific information on this particular radiocarbon-dated sample, Ramis and Alcover7 suggested that the bone fragment, initially identified as human, might actually belong to M. balearicus, an endemic bovid. Consequently, this sample was considered not relevant for determining the timing of the island’s colonization. Similarly, the radiocarbon dates from Cova de Canet were considered highly controversial because they originate from a charcoal layer that lacks clear evidence of human activity7,8. Furthermore, in neither of these caves do the M. balearicus bones show butchery marks, making it difficult to establish a clear link to contemporary human presence2. Due to the aforementioned issues these early results were deemed unreliable1,8,13.
Several studies have reevaluated most of the previously dated materials and supplemented them with new radiocarbon dates obtained from charcoal, ash, and bones6,7,9,10. Based on these new results, there is now a consensus that the timeframe for earliest human settlement on the island is between 4600 and 4200 cal B.P.14.
Dawson2 presents a synthesis of the various lines of argument regarding arrival models in the Balearic islands that includes: (1) Early (~9000 cal B.P.), (2) Intermediate (~7600 cal B.P.), and (3) Late (~5000 cal B.P.) arrival phases. The last two models suggest the existence of stable settlements, yet only the third one has been deemed plausible in the local archeological literature7,8,14.
While there has been a growing body of evidence revealing progressively earlier human settlements on many islands in the Mediterranean basin, the timeline for the initial human colonization in Mallorca has seen relatively minor adjustments over the past decades8,15,16. The latest research suggests that this colonization occurred approximately 4400 cal B.P., coinciding with the human-mediated extinction of Myotragus balearicus14. This conclusion is based on two radiocarbon ages, which provide a relatively narrow time window of 350 years (p > 90%) between the last documented Myotragus bone (4581–4417 cal B.P.) and the first dated sheep bone (4417–4231 cal B.P.). However, it remains challenging to confirm whether the ages of these paleontological remains represent the latest or the earliest such occurrences on the island. Subsequent field work may shed light on this matter.
Our study site is a submerged archeological structure in the Genovesa Cave (also known as Cova de’n Bessó; 39°31’32” N, 3°19’2” E), situated in the eastern part of Mallorca (Fig. 1a, b). The cave hosts ceramic sherds and stone constructions. The latter includes a stone-paved path that connects the cave entrance to the first underground lake (Fig. 1d), a cyclopean stone wall running parallel to the path, and an 8.62 m long17 and 0.5 m high stone walkway (hereafter referred as to bridge) oriented NE–SW (Fig. 1c, e, Supplementary Fig. 1, Supplementary Table 1). This last structure was built across a lake by stacking large limestone breakdown blocks on top of each other, without the use of mortar or cement. The uppermost layer comprises flat boulders of considerable size (Supplementary Fig. 1b). The largest stone measures 1.63 m in length and 0.6 m in width. Relative to the preindustrial (pre-1900 CE) sea level, the bridge is submerged by 1.05 ± 0.1 m of water at its upper part (Figs. 1e, 2). However, at the time of its construction, it served as an access path to the only other dry chamber in the cave (Sala de les Rates-pinyades, i.e., Bats Room), where pottery, tentatively attributed to the Naviform period (ca. 3550–3000 cal B.P.) was discovered18,19. The bridge structure was inferred to have been built around the same period20.
Fig. 1: Cave and sample locations.
a Map showing Mallorca in the western Mediterranean (black square). b Location of Genovesa and Drac caves; CCG: Closos de Can Gaià archeological site. c Plan of Genovesa Cave showing the location of the phreatic overgrowth on speleothems samples (yellow circles) and the survey station (red dot). d Photograph of the stone-paved path leading to the bridge (person height = 167 cm). e Cross-section (x–x’) indicating the location of the submerged bridge relative to the cave entrance and the present sea level. Maps (a, b) are available under CC Public Domain License from https://pixabay.com/illustrations/map-europe-world-earth-continent-2672639/ and https://pixabay.com/illustrations/mallorca-map-land-country-europe-968363/, respectively.
Fig. 2: Positional relationship between the bridge, preindustrial sea level, and analyzed samples.
The cross sections depict the spatial relationship between the submerged bridge and the U-series dated samples (phreatic overgrowth on speleothems: orange/yellow spindle; soda straw tips: red circle) from Genovesa and Drac caves. The vertical scale applies uniformly to all samples from both caves. All ages are reported as thousands of years (kyr) before present, where present is defined as 1950 CE.
Here, we integrate uranium-series (U-series) age data acquired from phreatic overgrowth on speleothems and stalactite tips in Genovesa and Drac caves, along with Late Holocene relative sea level (RSL) information available for Mallorca21. Additionally, we consider the presence of the bridge, the coloration mark on its upper part, and the depths at which these respective features occur. This combined evidence contributes valuable insights to the ongoing debate surrounding the timing of human colonization on Mallorca.
Because Creationists love to find fault with the geochronology in these records of pre-'Creation Week' events, I've included sections on geochronology here:
Results and discussion Speleothems and sea level
Proxies for cave-based sea-level reconstructions include mineralogical (sediments, speleothems)22,23, archeological (fish tanks, saltpans, submerged structures, etc.)24, and biological (borings, worm tubes, etc.)24 records. In the case of Genovesa Cave, a typical coastal karst feature situated <450 m from the shoreline, both mineralogical and archeological records are present. Many of its well-decorated passages, galleries, and chambers are now flooded due to rising sea levels20. Because of the cave’s proximity to the coast and the high permeability of the Upper Miocene host rock25, the hydraulic gradient is negligible (9 × 10-5 m /m) for such short distances (see Methods), and thus the water table in the cave is, and was in the past, coincident with sea 26,27. During times of high sea level stillstands, when the cave was partly flooded, distinct encrustations of calcite and aragonite accumulated over preexisting stalactites, forming the so-called phreatic overgrowths on speleothems28 (POS). This is a particularly useful proxy for precisely and accurately reconstructing sea-level changes across various timescales21,29. Furthermore, ordinary stalactites, which form in cave passages above the water table and later become submerged as sea-levels rise are also valuable in this process since they document the moment when the cave shifted from being air- to water-filled22.
A distinct light-colored band (~15 cm wide) is visible along the entire bridge at its upper part (Fig. 2, Supplementary Fig. 1a). This coloration mark bears a resemblance to a “bathtub ring” and its presence is likely related to a relatively short-lived stable water table that allowed the precipitation of a sub-millimeter calcite crust at the water/air interface. When the water level increased, the calcite did not disappear since the water below the water table remained somewhat saturated with respect to calcium carbonate. As discussed later, this feature along with the new POS ages and their elevation play a crucial role in determining when this bridge, now submerged, was constructed.
Geochronology
The U-series ages (n = 34; 28 for POS and 6 from stalactites) are given in Supplementary Table 2 and are all reported as years before present (BP), where present is 1950 CE. Ten of these ages are from POS samples GE-D8 (Genovesa Cave; Supplementary Fig. 2) and DR-D15 dated as part of a prior study21. The latter was collected in Drac Cave (39°32’9” N, 3°19’49” E), located 1.6 km to the north-east of Genovesa Cave (Fig. 1c, Supplementary Figs. S3–S4).
Regardless of the sampling depth, all the vadose stalactites on which the POS formed in both caves, produced ages older than 8200 years B.P. (Fig. 2, Supplementary Fig. 5). The phreatic overgrowth samples GE-D6, GE-D7, and DR-D23 (Supplementary Figs. S6–S8), precipitated at ~1.10 ± 0.1 m below the preindustrial sea level (mbpsl). A 232Th/238U-234U/238U-230Th/238U (plotted as a Rosholt A type) isochron age of 5479 ± 120 years B.P. (n = 3 of 4; hereafter, ± refers to 2 σ uncertainty) was measured for GE-D6 (Supplemental Table 2, Supplementary Fig. 9a). GE-D7, in the same room and at the same elevation as GE-D6, yielded a weighted average age of 5510 ± 549 years B.P. using the same correction (initial 230Th/232Th atomic ratio = 5.1 ± 0.4 ppm) generated by the GE-D6 isochron age. Onac et al.21. used a slightly higher initial for GE-D8 (8 ppm) that was located at a higher elevation than GE-D6 & -D7. For DR-D23, we obtained a 232Th/238U-234U/238U-230Th/238U (plotted as a Rosholt A type) isochron age of 5824 ± 140 years B.P. (n = 6) (Supplementary Table 2, Supplementary Fig. 9b). This isochron shows an exceptionally high initial 230Th/232Th atomic ratio = 527.5 ± 22.1 ppm, more than 10x higher than used for DR-D15 (44 ppm) from the same cave but at a different elevation21. The fluffy fibrous cotton-candy texture of the two sub-samples with high U component of DR-D23 may have something to do with the high initial 230Th/232Th. The isochron ages were necessary to produce accurate ages with smaller uncertainties.
Collectively, the POS data from Genovesa and the nearby Drac, reveal three distinct periods of relative sea-level stability (Fig. 2). One occurred at 0 ± 0.04 m from 2720 ± 11 to 296 ± 18 years B.P. The second period lasting from 3703 ± 14 to 3368 ± 8 years B.P., corresponds to a sea level of 0.25 mbpsl. Lastly, a third period at ~1.1 ± 0.1 mbpsl is documented between 5820 ± 140 and 5479 ± 120 years B.P. (Figs. 2, 3). By adding the uncertainty to the older age and subtracting the uncertainty from the younger age, the maximum time span of POS growth at 1.1 mbpsl ranges from 5964 – 5359 years B.P. During this interval, both the POS and the coloration mark formed. For the latter to develop, the bridge must have been submerged, at least to its upper surface, allowing calcite to precipitate during the sea-level stillstand. Therefore, this period is of particular interest because it may aid in providing the timeline of the bridge construction as detailed below.
Timing of bridge construction
The assembly date of the bridge in Genovesa Cave remains uncertain due to the absence of written records or a robust time-stratigraphic context. In order to constrain the building time of this archeological structure, we rely on a well-defined Late Holocene sea-level curve generated by Onac et al.21. for Mallorca (depicted by the solid blue line in Fig. 3) and the ages and depths at which POS grew and coloration mark formed. First, we assess previous assumptions regarding the timing of the submerged bridge construction using this curve. Then, we examine our new sea-level data in conjunction with the timing of the earliest human arrival model proposed by Bover et al.14.
The prehistoric pottery discovered in Sala de les Rates-pinyades of the Genovesa Cave has been linked to the Naviform period (3550–3000 cal B.P.). This attribution is based on typological similarities between the ceramics found in Genovesa and those documented at the Closos de Can Gaià, a Bronze Age site located ~10 km south of our cave (Fig. 1b). The archeological horizon in which comparable pottery was discovered at the latter site was dated to ~3600 cal B.P30. However, Costa and Guerrero31 argue that Closos de Can Gaià excavation required a reassessment of the chronological framework, due to issues with the radiocarbon dates. Despite this, adopting the previously reported radiocarbon age, Gràcia et al.20 suggested that the construction of the bridge likely occurred toward the end of the Naviform period.
However, the RSL curve (Fig. 3) indicates that sea level was ~0.25 ± 0.1 m below the preindustrial baseline ~3500 years ago21, implying a total water depth of ~1.3 m in the cave lake. The vertical height of the bridge is 0.5 m, and thus it was submerged by 0.8 m of water at this time (Fig. 3). The construction of the bridge around 4400 years ago, the time suggested by Bover et al.14 to be the earliest evidence of human presence on the island, is also improbable. At that time, relative sea level in Mallorca was ~0.35 ± 0.1 m below preindustrial level, and the bridge would have been submerged by 0.7 m. Building a bridge below water level is a highly unlikely scenario, and thus it was likely built at an earlier time, when sea level was lower. The predicted relative sea-level curve for Mallorca (Fig. 3) indicates that the top of the bridge would have been close to water level no earlier than 5600 years ago and this provides an approximate lower bound on the age of the feature. The distinct coloration mark on the bridge also provides strong evidence of an age greater than the ages estimated by Gràcia et al.20 and Bover et al.14. As discussed earlier and according to the POS-based relative sea-level record, this mark would not have developed if the top of the bridge was well below the water level, i.e., at times more recent than ~5500 years ago. However, an age older than 6000 years for the feature can be ruled out since sea level was even lower (Fig. 3), and the construction of a bridge at its current height would have been unnecessary.
Fig. 3: Proposed timing for bridge construction.
Comparison between the position of the submerged bridge, phreatic overgrowth on speleothems (POS), coloration mark, and the RSL prediction (blue curve)21 based on a Glacial Isostatic Adjustment model that uses the ICE-6G (VM 5) ice history with an upper mantle viscosity of 1.3 × 1020 Pa s. Solid symbols with age and depth uncertainties represent POS elevations. The brown rectangle depicts the bridge with its coloration band in the upper part. The insets show an underwater image of the bridge (Photo courtesy of R. Landreth) and a close-up view on the RSL position of samples GE-D6, GE-D7, and DR-D23 that grew at 1.1 mbpsl. The uncertainties for GE-D6, GE-D7, and DR-D23 are absolute 2 σ error bars based on three dimensional isochron ages or weighted average (GE-D7). The dotted blue line is a sea-level rise scenario that includes the brief stillstand inferred from the POS growth.
The phreatic overgrowths GE-D6, GE-D7, and DR-D23 from Genovesa and Drac caves formed at a relative sea level of 1.1 mbpsl, which is 5 cm below the upper part of the bridge. The two more precise isochron ages suggest sea-level remained relatively constant for a few hundreds of years between ~5964 and 5359 years B.P. The relative brevity of this time frame might explain why the morphology and size of the POS are somehow atypical and smaller compared to those POS that developed when the sea level was stable at 0 m for over 2000 years. Furthermore, this <600 year period of nearly constant sea level was sufficient to develop the coloration mark. Given that the occurrence of this feature correlates directly with the previously mentioned sea-level stillstand position, it suggests that the bridge was already in place. In fact, its construction could have commenced as early as ~6000 years ago when the water depth in the lake was ~0.25 m. However, it had to be completed before ~5600 years ago when the sea-level rose to the top surface of the bridge.
Lots of stuff for creationists to lie about there. Firstly, there is the record of sea-level changes reflecting the advance and retreat of ice sheets over the past few tens of thousands of years.
Then there is the record of human habitation and construction of the bridge when creationist mythology says the world was subject to a genocidal flood in which all life was extinguished save a small handful of survivors that then repopulated the planet in just a few thousand years.
What a creationist now needs to do is explain why all the dating methods, which converge on these dates, are all wrong and should be converging on a much more recent date compatible with creation of Earth from nothing just 10,000 years ago and all human life originating from 8 related individuals just 4,000 years ago.
Sadly, because the authors of these myths knew nothing of the real history of the Western Mediterranean, the book they wrote, and which creationists think is a real history book, is entirely silent on the matter.
Although both have evolved from a segmented ancestor, as can still be seen in the larvae of insects, spiders and mites differ from insects in the number of major body-parts. While insects have well-defines head, thorax (to which wings and legs are attached) and an abdomen, where the reproductive organs or normally located, spiders, scorpions, tics and mites (arachnids or chelicerates) have just two - a cephalothorax, combining the head and thorax, and an abdomen.
Now scientists have discovered a gene in the chelicerates that controls the development of the 'waist' between the cephalothorax and the abdomen, which is missing in insects. The loss of this gene could be the reason the two groups of arthropods evolved in different directions.
The team of scientists, led by Emily V. W. Shetton, of the Department of Integrative Biology, University of Wisconsin-Madison, Madison, Wisconsin, USA, have just published their findings, open access, in PLOS Biology and explained it in a press release reprinted in Science Daily:
The research team also included: Jesús A. Ballesteros of the Department of Biology, Kean University, Union, New Jersey, USA and Pola O. Blaszczyk, Benjamin C. Klementz, and Prashant P. Sharma all of Department of Integrative Biology, University of Wisconsin-Madison.
Because they were so ignorant of the history of their part of the world, the origin myths made up by the Bronze Age authors of Genesis, told us nothing about the rich history of the sea that was almost on their doorstep, and the one in which they set daft tales like that of Jonah - the Mediterranean.
The Mediterranean Sea (the sea in the Middle of the Earth to the Romans) was central to history of the Middle East, Western Europe and North Africa but few people then could have been aware that the sea itself is a mere (on a geological timescale) 5.5 million years old in its present form.
It was formed firstly by the African plate pushing north towards Eurasia causing a water-filled depression to form that was originally connected to the Atlantic Ocean, but, as Africa pushed further north, causing mountains in modern-day Morocco and Spain to rise up, the Mediterranean became isolated and, with low inflow and high temperatures, what had been the Mediterranean Sea became a salt-filled depression, known to geologists as the Messinian Salinity Crisis (MSC) when the sea dried up leaving a thick deposit of salt and gypsum and of course exterminating just about all marine life.
Recreation of one of the proposed models for how the Mediterranean was isolated by the sinking of a lithospheric plate into the Earth’s mantle (approx. 6 million years ago) and how dry climate then lead to the desiccation of that sea during the Messinian Salinity Crisis (approx. 5.5 million years ago), until 5.33 million years ago, the level of the Atlantic exceeded that of the Gibraltar land bridge and triggered a fast refill.
This was ended abruptly when the Atlantic Ocean broke through at the Western end in what is now the Straits of Gibraltar when the Mediterranean basin refilled extremely quickly, possible in a few months to two years.
The bad news for creationists continues unabated as science discovers more facts, as we would expect of a counter-factual superstition.
This time it's news that new research led by University of Utah geoscientists has shown how there is a record of climate change in the fossil record in the form of traces of boron isotopes in the fossilised shells of microscopic foraminifera.
The record, 59-51 million years before creationists think Earth was created, is just another record of events in that 99.9975% of Earth's history that creationists try to shoe-horn into 10,000 to make it seem like their childish creation myth has some merit.
The record of change itself depends not on radioactive decay rates but on the ratios of stable isotopes of boron that get incorporated in the shells of microscopic foraminifera during their growth and then remain locked up as their bodies fossilise in marine sediment.
Dating of this marine sediment is done using several strands of evidence, one of which is U-Pb dating of zircon crystals, and all of which converge on the same dates (see the AI panel on the right).
What changes is the ratio of 11B (δ11B) incorporated in the shells of foraminifera during their lifetime, and this is related to the pH of the seawater. pH of sea water is in turn determined by the level of atmospheric CO2 - the higher the level of CO2, the lower the pH due to dissolved carbonic acid H3CO4.
This article is best read on a laptop, desktop or tablet
The 'Pillars of Creation'.
The 'fine-tuned Universe' argument appeals particularly to those who understand neither physics nor probability and for whom the argument from ignorant incredulity and the false dichotomy fallacies are compelling, partly due to parochial ignorance in assuming that the locally popular god is the only entity capable of creating a universe, and that nothing else, supernatural or otherwise is capable of it.
The most compelling argument against it is the anthropic principle. This means the fact that we are discussing it means we must exist in a universe in which intelligent life is certain.
There is also the subtle blasphemy that most creationists seem not to have thought of in that the argument assumes their putative creator god could only create life within fine-tuned' parameters, so is itself constrained by the same parameters. This denies it's omnipotence and implies the existence of a higher power which set these constraints.
Incidentally, although it's not strictly speaking an argument against the 'fine-tuned' fallacy, note that one of the fundamental forces is the weak nuclear force which governs the rate of radioactive decay. Creationists try to dismiss geochronology based on radiometric dating, claiming, with no evidence whatsoever, that the decay rates used to be much faster, so millions of years can look like 10,000 years or less. This would mean the weak nuclear force was even weaker, by several orders of magnitude.
Probability of dealing a specific bridge hand from a 52-card pack:
\[
P = \frac{1}{\binom{52}{13} \times \binom{39}{13} \times \binom{26}{13} \times \binom{13}{13}}
\]
Which can be simplified to:
\(
P = \frac{1}{\frac{52!}{(13!)^4}}
\) or \(
P \approx 1.86 \times 10^{-29}
\)
Creationists will look at a tiny probability like this and conclude that dealing four bridge hands from a 52-card pack is so improbable as to be impossible, therefore a god must have dealt the cards, and then wave that 'fact' as 'proof' of the locally popular god.
If that were true, as the following dialogue shows, the formation of anything other than hydrogen would not be possible, so stars (which depend on the nuclear fusion of hydrogen to form helium to prevent them collapsing under their own gravity) could not exist, nor could the heavier elements of which living organisms are composed.
Creationists are, probably because they lack the understanding to realise it, and their 'scientists' aren't going to tell them, arguing two mutually contradictory claims simultaneously. They can't both be right, but they can both be wrong.
Of course, given their willingness to try to mislead gullible people into joining their cult, we can never be sure that creationists who try to get away with this fallacy aren't aware they are using a false argument in order to deceive.
The following is a dialogue with ChatGPT4.0, which not only debunks the argument, but shows how it's actually a blasphemy because it argues more strongly against a supreme, omnipotent creator god than for one:
Fungi, like some primitive plants such as ferns and mosses reproduce with spores - tiny packages that contain the entire genome of the parent which have the capacity to grow and develop into a new adult able to produce spores of its own. The key to success is getting those spores dispersed and how a fungus manages that will depend on the environment in which it lives and reproduces.
Most fungi use wind dispersal, their spores being light enough to be carried considerable distances but where they land is a matter of chance, so must wind-dispersed fungi produce millions of spores to give them a good chance of just one or two landing in a suitable place.
A few others have evolved a different, more targeted strategy such as being eaten by animals and excreted in their faeces. This increases the chance of being deposited in the same environment in which the parent fungi lived as the dispersing animal also lives in that environment. This is the method adopted by truffles which produce their fruiting body (where the spores are produced) underground and emit a scent which is attractive to the target animal (pigs, dogs, etc.) which dig up the fruiting body and eventually disperse the spores. This is probably the reason that humans like the taste of truffles, although we lack the ability to sniff them out for ourselves, but possibly an early ancestral species could.
But what happens to these fungi if there are no mammals, other than bats, as was the case with New Zealand before humans brought their commensal species with them? This is the subject of an article in The Conversation by three experts: Jamie Wood, Senior Lecturer in Ecology and Evolution, University of Adelaide, Australia, and Amy Martin, Post-Doctoral Researcher in Evolutionary Ecology and Anne Gaskett, Associate Professor of Biology, both of the University of Auckland, Waipapa Taumata Rau, New Zealand.
Their article is reproduced here under a Creative Commons license, reformatted for stylistic consistency:
One of creationism's putative major success in the last 100 years, has been its new (as of 2019) coronavirus, SARS-CoV-2 (Severe Acute Respiratory Syndrome – Corona Virus - 2.
Creationist have been fooled by their cult to believe that the Universe is 'fine-tuned' for life and that this 'fine-tuning' is proof of their particular god and its particular holy book.
This is a blatant false dichotomy fallacy; even if it could be proved to be true by showing that the various (and usually ill-defined) parameters could have other values it does not follow that a randomly designated god is responsible for 'tuning' them.
It's also a blasphemy, if creationists did but realise it, because it assumes their supposedly omnipotent god is itself constrained by the fundamental laws of chemistry and physics and could only work to create life within very narrow constraints - which implies a higher power to set that constraint.
How many black holes are there in the known Universe?
Estimating the exact number of black holes in the known Universe is challenging, but astronomers have made some educated guesses based on our current understanding.
Stellar-Mass Black Holes
Stellar-mass black holes, which form from the collapse of massive stars, are the most common type. Based on the number of stars in the Universe and the fraction of those stars that are massive enough to form black holes, it is estimated that there are around 100 million to 1 billion stellar-mass black holes in the Milky Way galaxy alone. Given that the Milky Way is just one of about 2 trillion galaxies in the observable Universe, the number of stellar-mass black holes across the Universe could be in the range of \({10^{18}}\) to \({10^{19}}\) (a billion trillion to 10 billion trillion).
Supermassive Black Holes
Supermassive black holes, which exist at the centers of galaxies, are much rarer. Almost every galaxy with a significant size is thought to have a supermassive black hole at its center. This suggests there could be around 2 trillion supermassive black holes in the observable Universe, one for each galaxy.
Primordial Black Holes
There is also the theoretical possibility of primordial black holes, which might have formed in the early Universe. These could range in mass from very small to large and could number in the vast quantities, though their existence has not been confirmed.
Total Estimate
In total, combining these different types, the number of black holes in the observable Universe could be as high as \({10^{19}}\) or more. This estimate is still very rough, as it depends on many factors, including the formation rates of black holes, the life cycle of stars, and the evolution of galaxies.
But it is nonsensical for another reason: life is not the most abundant manifestation of the laws of physics in the Universe; that honour goes more deservedly to black holes, of which there are estimated \(\small {10^{19}}\) in the observable Universe - far more than there are living organisms - and black holes don't require special conditions in which to exist, other than a Universe with enough mass.
And black holes, far from showing that the Universe is a place designed to be friendly to life (which only the most parochial and naive simpletons could imagine, given that most of it above a few thousand feet of the surface of Earth is hostile to most forms of life and only a fraction of the surface is hospitable without special adaption or complex technology), are about the most destructive thing in the Universe, reducing everything that comes within their event horizon to energy which can only escape in the form of Hawking radiation.
So, if anything, the Universe appears to be 'fine-tuned' for self-destruction and the eventual extermination of life. Not exactly what the creation cults want their dupes to believe.
This theory has the advantage of a possible explanation for the appearance of design just as living organisms have, in the form of the Theory of Evolution. Black holes are believed to contain the quantum conditions for universes to spontaneously arise, so, if there were a mechanism for passing information through a black hole from the parent universe to a descendant one, natural selection should mean universes get better at making black holes.
How black holes swallow up entire suns, compete with any orbiting planets is the subject of a recent paper in Astrophysical Journal Letters which show computer generated simulations of the event. One notable observation if the 'spaghettification' effect where, from the point of view of a distant observer, an object falling into a black hole becomes drawn out into a thin string, like toothpaste out of a tube. This is caused by the dilation of space and time due to the increasing gravity as the black hole is approached and is an effect of General Relativity.
One of the authors of this paper, Professor Daniel Price of Monash University, Australia, has published an article about the team's findings in The Conversation. His article is reprinted here under a Creative Commons license, reformatted for stylistic consistency:
Watch a star get destroyed by a supermassive black hole in the first simulation of its kind
Giant black holes in the centres of galaxies like our own Milky Way are known to occasionally munch on nearby stars.
This leads to a dramatic and complex process as the star plunging towards the supermassive black hole is spaghettified and torn to shreds. The resulting fireworks are known as a tidal disruption event.
In a new study published today in the Astrophysical Journal Letters, we have produced the most detailed simulations to date of how this process evolves over the span of a year.
A black hole tearing apart a sun
American astronomer Jack G. Hills and British astronomer Martin Rees first theorised about tidal disruption events in the 1970s and 80s. Rees’s theory predicted that half of the debris from the star would remain bound to the black hole, colliding with itself to form a hot, luminous swirl of matter known as an accretion disc. The disc would be so hot, it should radiate a copious amount of X-rays.
An artist’s impression of a moderately warm star – not at all what a black hole with a hot accretion disc would be like.
But to everyone’s surprise, most of the more than 100 candidate tidal disruption events discovered to date have been found to glow mainly at visible wavelengths, not X-rays. The observed temperatures in the debris are a mere 10,000 degrees Celsius. That’s like the surface of a moderately warm star, not the millions of degrees expected from hot gas around a supermassive black hole.
Even weirder is the inferred size of the glowing material around the black hole: several times larger than our Solar System and expanding rapidly away from the black hole at a few percent of the speed of light.
Given that even a million-solar-mass black hole is just a bit bigger than our Sun, the huge size of the glowing ball of material inferred from observations was a total surprise.
While astrophysicists have speculated the black hole must be somehow smothered by material during the disruption to explain the lack of X-ray emissions, to date nobody had been able to show how this actually occurs. This is where our simulations come in.
A slurp and a burp
Black holes are messy eaters – not unlike a five-year-old with a bowl of spaghetti. A star starts out as a compact body but gets spaghettified: stretched to a long, thin strand by the extreme tides of the black hole.
As half of the matter from the now-shredded star gets slurped towards the black hole, only 1% of it is actually swallowed. The rest ends up being blown away from the black hole in a sort of cosmic “burp”.
Simulating tidal disruption events with a computer is hard. Newton’s laws of gravity don’t work near a supermassive black hole, so one has to include all the weird and wonderful effects from Einstein’s general theory of relativity.
But hard work is what PhD students are for. Our recent graduate, David Liptai, developed a new do-it-Einstein’s-way simulation method which enabled the team to experiment by throwing unsuspecting stars in the general direction of the nearest black hole. You can even do it yourself.
Spaghettification in action, a close up of the half of the star that returns to the black hole.
The resultant simulations, seen in the videos here, are the first to show tidal disruption events all the way from the slurp to the burp.
They follow the spaghettification of the star through to when the debris falls back on the black hole, then a close approach that turns the stream into something like a wriggling garden hose. The simulation lasts for more than a year after the initial plunge.
Zoomed-out view, showing the debris from a star that mostly doesn’t go down the black hole and instead gets blown away in an expanding outflow.
What did we discover?
To our great surprise, we found that the 1% of material that does drop to the black hole generates so much heat, it powers an extremely powerful and nearly spherical outflow. (A bit like that time you ate too much curry, and for much the same reason.)
When observed like they would be by our telescopes, the simulations explain a lot. Turns out previous researchers were right about the smothering. It looks like this:
The same spaghettification as seen in the other movies, but as would be seen with an optical telescope [if we had a good-enough one]. It looks like a boiling bubble. We’ve called it the “Eddington envelope”.
The new simulations reveal why tidal disruption events really do look like a solar-system-sized star expanding at a few percent of the speed of light, powered by a black hole inside. In fact, one could even call it a “black hole sun”.
Daniel Price, Professor of Astrophysics, Monash University
Published by The Conversation. Open access. (CC BY 4.0)
For the technically-minded, more detail is given in the paper in Astrophysical Journal Letters:
Any creationists wishing to refute this paper will need to refute the details given here:
Abstract
Stars falling too close to massive black holes in the centres of galaxies can be torn apart by the strong tidal forces. Simulating the subsequent feeding of the black hole with disrupted material has proved challenging because of the range of timescales involved. Here we report a set of simulations that capture the relativistic disruption of the star, followed by one year of evolution of the returning debris stream. These reveal the formation of an expanding asymmetric bubble of material extending to hundreds of astronomical units — an outflowing Eddington envelope with an optically thick inner region. Such outflows have been hypothesised as the reprocessing layer needed to explain optical/UV emission in tidal disruption events, but never produced self-consistently in a simulation. Our model broadly matches the observed light curves with low temperatures, faint luminosities, and line widths of \(\small {10,000}–{20,000}\;\text{km/s}\).
1 Introduction
In the classical picture of tidal disruption events (TDEs), the debris from the tidal disruption of a star on a parabolic orbit by a supermassive black hole (SMBH) rapidly circularises to form an accretion disc via relativistic apsidal precession (Rees, 1988). The predicted mass return rate of debris (Phinney, 1989) is \(\small \propto t^{5/3}\) and the light curve is assumed to be powered by accretion and to follow the same decay.
This picture alone does not predict several properties of observed TDEs, mainly related to their puzzling optical emission (van Velzen et al., 2011; van Velzen, 2018; van Velzen et al., 2021). These properties include: i) low peak bolometric luminosities (Chornock et al., 2014) of \(\small \sim {10^{44}}\;\text{ergs/s}\) \(\small \sim\) 1 per cent of the value expected from radiatively efficient accretion (Svirski et al., 2017); ii) low temperatures, more consistent with the photosphere of a B-type star than with that of an accretion disc at a few tens of gravitational radii (\(\small R_{g}\equiv GM_{\mathrm{BH}}/c^{2}\)) (Gezari et al., 2012; Miller, 2015), and consequently large emission radii, \(\small \sim {10}-{100}\) au for a \(\small 10^{6}M_{\odot}\) black hole (Guillochon et al., 2014.1; Metzger & Stone, 2016); and iii) spectral line widths implying gas velocities of \(\small \sim {10^4}\;\text{km/s}\), much lower than expected from an accretion disc (Arcavi et al., 2014.2; Leloudas et al., 2019; Nicholl et al., 2019.1).
As a consequence, numerous authors have proposed alternative mechanisms for powering the TDE lightcurve, via either shocks from tidal stream collisions during disc formation (Lodato, 2012.1; Piran et al., 2015.1; Svirski et al., 2017; Ryu et al., 2023; Huang et al., 2023.1), or the reprocessing of photons through large scale optically thick layers, referred to as Eddington envelopes (Loeb & Ulmer, 1997), super-Eddington outflows (Strubbe & Quataert, 2009), quasi-static or cooling TDE envelopes (Roth et al., 2016.1; Coughlin & Begelman, 2014.3; Metzger, 2022) or mass-loaded outflows (Jiang et al., 2016.2; Metzger & Stone, 2016). Recent spectro-polarimetric observations suggest reprocessing in an outflowing, quasi-spherical envelope (Patra et al., 2022.1).
The wider problem is that few calculations exist that follow the debris from disruption to fallback for a parabolic orbit with the correct mass ratio. The challenge is to evolve a main-sequence star on a parabolic orbit around a SMBH from disruption and to follow the subsequent accretion of material (Metzger & Stone, 2016). The dynamic range involved when a \(\small 1M_{\odot}\) star on a parabolic orbit is tidally disrupted by a \(\small {10^6}_{\odot}\) SMBH is greater than four orders of magnitude: the tidal disruption radius is 50 times the gravitational radius, where general relativistic effects are important, while the apoapsis of even the most bound material is another factor of 200 further away. This challenge led previous studies to consider a variety of simplifications (Stone et al., 2019.2): i) reducing the mass ratio between the star and the black hole by considering intermediate mass black holes (Ramirez-Ruiz & Rosswog, 2009.1; Guillochon et al., 2014.1); ii) using a Newtonian gravitational potential (Evans & Kochanek, 1989.1; Rosswog et al., 2008; Lodato et al., 2009.2; Guillochon et al., 2009.3; Golightly et al., 2019.3), pseudo-Newtonian (Hayasaki et al., 2013; Bonnerot et al., 2016.3) or post-Newtonian approximations (Ayal et al., 2000; Hayasaki et al., 2016.4); iii) simulating only the first passage of the star (Evans & Kochanek, 1989.1; Laguna et al., 1993; Khokhlov et al., 1993.1; Frolov et al., 1994; Diener et al., 1997.1; Kobayashi et al., 2004; Guillochon et al., 2009.3; Guillochon & Ramirez-Ruiz, 2013.1; Tejeda et al., 2017.1; Gafton & Rosswog, 2019.4; Goicovic et al., 2019.5); and iv) assuming stars initially on bound, highly eccentric orbits instead of parabolic orbits (Sadowski et al., 2016.5; Hayasaki et al., 2013, 2016.4; Bonnerot et al., 2016.3; Liptai et al., 2019.6; Hu et al., 2024).
These studies have, nevertheless, provided useful insights into the details of the tidal disruption process. In particular, it has been shown that the distribution of orbital energies of the debris following the initial disruption is roughly consistent with \(\small dM/dE\) = const, consistent with the analytic prediction of a \(\small \propto t^{5/3}\) mass fallback rate, although the details can depend on many factors such as stellar spin, stellar composition, penetration factor and black hole spin (Lodato et al., 2009.2; Kesden, 2012.2; Guillochon & Ramirez-Ruiz, 2013.1; Golightly et al., 2019.3; Sacchi & Lodato, 2019.7). The importance of general relativistic effects in circularising debris has also been demonstrated. The self-intersection of the debris stream, which efficiently dissipates large amounts of orbital energy, is made possible by relativistic apsidal precession (Hayasaki et al., 2016.4; Bonnerot et al., 2016.3; Liptai et al., 2019.6; Calderón et al., 2024.1). But until recently debris circularisation has only been shown for stars on bound orbits, with correspondingly small apoapsis distances and often deep penetration factors (we define the penetration factor as \(\small \beta\equiv R_{\mathrm{t}}/R_{\mathrm{p}}\), where \(\small R_{\mathrm{t}}=R_{*}(M_{\mathrm{BH}}/M_{*})^{1/3}\) is the tidal radius and \(\small R_{\mathrm{p}}\) is the pericenter distance).
Recent works have shown that circularisation and initiation of accretion is possible in the parabolic case, by a combination of energy dissipation in the ‘nozzle shock’ that occurs on second pericenter passage (Steinberg & Stone 2024.2; but see Bonnerot & Lu 2022.2 and Appendix E for convergence studies of the nozzle shock) and/or relativistic precession leading to stream collisions (Andalman et al., 2022.3).
In this paper, we present a set of simulations that self-consistently evolve a one solar mass polytropic star on a parabolic orbit around a \(\small {10^6}\) solar mass black hole from the star’s disruption to circularization of the returning debris and then accretion. We follow the debris evolution for one year post-disruption, enabling us to approximately compute synthetic light curves which appear to match the key features of observations.
Figure 1:One year in the life of a tidal disruption event. We show shapshots of column density in the simulation of a \(\small 1M_{\odot}\) star on a parabolic orbit with \(\small \beta = {1}\), disrupted by a \(\small {10^6} M_{\odot}\) black hole, using \(\small 4\times 10^{6}\) SPH particles in the Schwarzschild metric. Main panel shows the large scale outflows after 365 days projected in the \(\small {x}-{y}\) plane with log scale. Inset panels show the stream evolution on small scales (\(\small{100}\times {100}\) au), showing snapshots of column density projected in the \(\small {x}-{y}\) plane on a linear scale from \(\small {0}\;\text{to}\; {1500}\;{g/cm^2}\) (colours are allowed to saturate). Animated versions of this figure are available in the online article. Data and scripts used to create the figure are available on Zenodo:https://doi.org/10.5281/zenodo.11438154 (catalog doi:10.5281/zenodo.11438154)
The Universe is far from the ideal environment for life to thrive in - known life only exists as an encrustation on or near the surface of a single planet. Instead, it is a violent and unstable chaos of competing forces with an estimated \(\small {10^{19}}\) supper-dense, massive black holes, which far exceeds the number of life forms in the known Universe, drawing to inevitable annihilation any body that strays too close.
It requires parochial ignorance of the first order to imagine that the entire Universe is designed for life. It is far easier to make a case for it being designed for black holes, although that, as with the 'designed for life' case, case would require a priori evidence of the existence of a creative entity in the form of an explanation of its origins and definitive evidence of it ever being recorded as creating anything. And by recorded, I don't mean written in the mythology of Bronze Age pastoralists who thought the Universe was a small flat place with a dome over it and containing nothing that was unknown within a day or two's walk of the Canaanite Hills where they grazed their goats, and later decreed to be literal history by people with a vested interest in people believing the myths.
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What Makes You So Special? From The Big Bang To You
How did you come to be here, now? This books takes you from the Big Bang to the evolution of modern humans and the history of human cultures, showing that science is an adventure of discovery and a source of limitless wonder, giving us richer and more rewarding appreciation of the phenomenal privilege of merely being alive and able to begin to understand it all.
Available in Hardcover, Paperback or ebook for Kindle
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Ten Reasons To Lose Faith: And Why You Are Better Off Without It
This book explains why faith is a fallacy and serves no useful purpose other than providing an excuse for pretending to know things that are unknown. It also explains how losing faith liberates former sufferers from fear, delusion and the control of others, freeing them to see the world in a different light, to recognise the injustices that religions cause and to accept people for who they are, not which group they happened to be born in. A society based on atheist, Humanist principles would be a less divided, more inclusive, more peaceful society and one more appreciative of the one opportunity that life gives us to enjoy and wonder at the world we live in.
Available in Hardcover, Paperback or ebook for Kindle
