Early Jurassic marine life
Image credit: Nikolay Zverkov.
Friday 28 June 2024
Creationism in Crisis - A Mass Extinction Of Marine Species 183 Million Years Before Creation Week
Carbon cycle changes during the Toarcian Oceanic Anoxic Event
Creationists who claim, against all the evidence, that the Universe is 'fine-tuned' for life, might like to ignore a period in Earth's long pre-'Creation Week' history when Earth quite suddenly, in geological terms, became very hostile to marine life in particular, resulting in a lot of it dying.
This event, one of the mass extinction events, is known as the Toarcian Oceanic Anoxic Event (TOAE) which occurred some 183 million years ago when an increase in volcanic activity associated with the break-up of Pangea, sent atmospheric carbon dioxides (CO2) sky high (literally) precipitating global warming. This, in turn led to a rise in ocean temperatures and, because warm water holds less oxygen (O2) than cold water, marine oxygen levels fell, leaving widespread areas of anoxic marine sediment.
Now a team of archaeologists have discovered evidence in Italian limestone that confirms the cause of the mass extinction was anoxia due to elevated atmospheric CO2. How they discovered it is the subject of a Duke University news release:
Tell me about the Toarcian Oceanic Anoxic Event, please. The Toarcian Oceanic Anoxic Event (T-OAE)
Overview
The Toarcian Oceanic Anoxic Event (T-OAE) is a significant geological event that occurred during the Early Jurassic period, roughly around 183 million years ago. This event is characterized by widespread marine anoxia (lack of oxygen) and is marked by substantial environmental and biotic changes, including mass extinctions and notable carbon cycle perturbations.
Key Characteristics
Causes and Mechanisms
- Anoxia: The T-OAE is defined by the presence of black shales deposited in marine environments, which indicate prolonged periods of low oxygen conditions. These black shales are rich in organic carbon, signifying the preservation of organic matter due to anoxic bottom waters.
- Carbon Isotope Excursion: The event is associated with a pronounced negative carbon isotope excursion (CIE). This means there was a significant drop in the ratio of the stable isotopes \(^{13}C\) to \(^{12}C\) in marine carbonates and organic matter, reflecting changes in the global carbon cycle.
- Biotic Responses: There were substantial extinctions among marine organisms, particularly affecting ammonites, bivalves, and foraminifera. Terrestrial ecosystems were also impacted, with evidence of disruptions in plant communities.
- Volcanism: The T-OAE is linked to massive volcanic activity, particularly the emplacement of the Karoo-Ferrar large igneous province. Volcanism likely contributed to elevated CO₂ levels, global warming, and changes in ocean chemistry, including increased nutrient input that promoted marine productivity and subsequent anoxia.
- Global Spread: Evidence for the T-OAE has been found in sedimentary records from various locations around the world, indicating its global impact. Key locations include Europe (e.g., the Yorkshire coast of England), North America, and South America.
Consequences
- Volcanic Activity: The Karoo-Ferrar volcanic province released large amounts of greenhouse gases, such as CO₂ and methane, leading to global warming. This warming could have decreased oxygen solubility in seawater and destabilized methane hydrates, further amplifying greenhouse effects.
- Ocean Circulation: Changes in ocean circulation patterns due to warming could have contributed to the development of widespread anoxic conditions by stratifying the water column and reducing the ventilation of deep waters.
- Nutrient Overload: Increased weathering of continental rocks, driven by higher CO₂ levels and acid rain from volcanic emissions, could have led to enhanced nutrient flux into the oceans. This nutrient influx would have stimulated primary productivity (algal blooms), which upon decomposition, would have depleted oxygen levels in bottom waters, promoting anoxia.
Summary
- Mass Extinction: The anoxic conditions and associated environmental stressors led to a significant extinction event, affecting marine and terrestrial life. Marine anoxia would have been particularly detrimental to bottom-dwelling organisms and those with high oxygen requirements.
- Sedimentary Record: The deposition of organic-rich black shales provides a valuable record of the T-OAE. These sediments are used by geologists to study past oceanic conditions and biogeochemical cycles.
- Carbon Cycle Disruption: The negative carbon isotope excursion indicates major changes in the carbon cycle, possibly due to the release of isotopically light carbon from methane hydrates and organic matter.
The Toarcian Oceanic Anoxic Event (T-OAE) was a major Early Jurassic event characterized by widespread marine anoxia, significant carbon isotope excursions, and extensive biotic extinctions. It was likely driven by massive volcanic activity, which triggered global warming, changes in ocean circulation, and nutrient loading, leading to prolonged periods of anoxic conditions in the world's oceans. The event has left a profound impact on the geological and fossil record, providing insights into the interactions between climate, ocean chemistry, and life on Earth.
What is meant by δ\(^{238}U\) and why does a negative excursion in δ\(^{238}U\) indicate anoxia in marine sediment?
Understanding δ\(^{238}U\)
Anoxia and δ\(^{238}U\)
- Definition of δ\(^{238}U\)
δ\(^{238}U\) (delta-238 Uranium) is a notation used to describe the isotopic composition of uranium in a sample. It is expressed as the deviation in the ratio of the isotopes \(^{238}U\) to \(^{235}U\) relative to a standard reference material. This ratio is typically measured using mass spectrometry. The δ notation is given by: \[ \delta^{238}U = \left( \frac{ \left( \frac{^{238}U}{^{235}U} \right)_{sample} }{ \left( \frac{^{238}U}{^{235}U} \right)_{standard} } - 1 \right) \times 1000 \, ‰ \] This means δ\(^{238}U\) is reported in parts per thousand (per mil, ‰).- Reference Standards
The standard used for δ\(^{238}U\) measurements is typically an average crustal value or seawater value. Differences from this standard indicate various geochemical processes affecting uranium isotopes in the sample.Negative Excursion in δ\(^{238}U\) and Anoxia
- Uranium Isotopes in Marine Environments
Uranium exists in seawater predominantly as soluble U(VI) in the form of uranyl carbonate complexes. The isotopic composition of uranium in seawater is relatively homogeneous due to the long residence time of uranium. However, in reducing (anoxic) environments, uranium is reduced from U(VI) to U(IV), which is insoluble and precipitates out of the water column into sediments.- Isotopic Fractionation
During the reduction of U(VI) to U(IV), there is a preferential removal of the lighter isotope \(^{235}U\), leading to isotopic fractionation. This fractionation typically enriches the remaining seawater in \(^{238}U\) and depletes the sediments in \(^{238}U\). Therefore, sediments deposited under anoxic conditions will have a lower δ\(^{238}U\) value compared to those deposited under oxic conditions.
- Excursions in δ\(^{238}U\)
A "negative excursion" in δ\(^{238}U\) refers to a decrease in the δ\(^{238}U\) value in a sedimentary record. This indicates that the sediments became enriched in the lighter isotope \(^{235}U\) relative to \(^{238}U\), consistent with the fractionation process during uranium reduction.- Indication of Anoxia
A negative δ\(^{238}U\) excursion in marine sediments is a strong indicator of anoxic conditions because:
- Under anoxic conditions, uranium is reduced from its soluble hexavalent state (U(VI)) to an insoluble tetravalent state (U(IV)).
- This process preferentially removes \(^{235}U\) from seawater, leaving a higher proportion of \(^{238}U\) in solution.
- The deposited sediments under these conditions become depleted in \(^{238}U\), resulting in a lower δ\(^{238}U\) value.
- This isotopic signature is preserved in the sediment record, providing evidence of past anoxic events.
Summary
- δ\(^{238}U\) is a measure of the isotopic composition of uranium in a sample relative to a standard.
- A negative δ\(^{238}U\) excursion in marine sediments indicates an enrichment of \(^{235}U\) relative to \(^{238}U\), suggesting uranium reduction.
- Uranium reduction occurs under anoxic conditions, leading to the precipitation of \(^{235}U\)-enriched U(IV) in sediments.
- Therefore, a negative δ\(^{238}U\) excursion serves as a proxy for past anoxic conditions in the marine environment.
Ocean’s Loss of Oxygen Caused Massive Jurassic Extinction. Could it Happen Again?
Researchers have found a chemical clue in Italian limestone that explains a mass extinction of marine life in the Early Jurassic period, 183 million years ago. Volcanic activity pumped out CO2, warming oceans and lowering their oxygen levels. The findings may foretell the impact climate change and oxygen depletion might have on today’s oceans.
Researchers have discovered a clue in Italian limestone that helps explain a mass extinction of marine life millions of years ago, and may provide warnings about how oxygen depletion and climate change could impact today’s oceans.
This event, and events like it, are the best analogs we have in Earth's past for what is to come in the next decades and centuries.
Assistant Professor Michael A. Kipp, co-author
Nicholas School of the Environment
Division of Earth and Climate Science
Duke University, Durham, NC, USA.
Kipp co-authored a study published June 24 in the Proceedings of the National Academy of Sciences that measures oxygen loss in oceans leading to the extinction of marine species 183 million years ago.
During the Jurassic Period, when marine reptiles like ichthyosaurs and plesiosaurs thrived, volcanic activity in modern South Africa released an estimated 20,500 gigatons of carbon dioxide (CO2) over 500,000 years. This heated the oceans, causing them to lose oxygen.
The result was the suffocation and mass extinction of marine species.
Studying limestone sediment that carries chemicals dating back to the time of the volcanic outburst, researchers were able to estimate the change in oxygen levels in ancient oceans. At one point, oxygen was completely depleted in up to 8% of the ancient global seafloor, an area roughly three times the size of the United States.It’s an analog, but not a perfect one, to predict what will happen to future oxygen loss in oceans from human-made carbon emissions, and the impact that loss will have on marine ecosystems and biodiversity.
Assistant Professor Mariano Remírez, co-corresponding author
Department of Atmospheric, Oceanic, and Earth Sciences
George Mason University, Fairfax, VA, USA.
Since the Industrial Revolution began in the 18th and 19th centuries, human activity has released CO2 emissions equivalent to 12% of what was released during the Jurassic volcanism.
But Kipp said that today’s rapid rate of atmospheric CO2 release is unprecedented in history, making it hard to predict when another mass extinction might occur or how severe it might be.
CITATION: “Carbonate Uranium Isotopes Record Global Expansion of Marine Anoxia During the Toarcian Oceanic Anoxic Event,” Mariano N. Remírez, Geoffrey J. Gilleaudeau, Tian Gan, Michael A. Kipp, François L. H. Tissot, Alan J. Kaufman, Mariano Parente. PNAS, June 24, 2024. DOI: 10.1073/pnas.2406032121We just don't have anything this severe. We go to the most rapid CO2-emitting events we can in history, and they're still not rapid enough to be a perfect comparison to what we're going through today. We're perturbing the system faster than ever before. We have at least quantified the marine oxygen loss during this event, which will help constrain our predictions of what will happen in the future.
Assistant Professor Michael A. Kipp.
Online: www.pnas.org/doi/10.1073/pnas.2406032121
Significance
A significant negative δ\(^{238}U\) excursion (~0.4‰) starting just prior to the onset of the negative carbon isotope excursion within the Toarcian Oceanic Anoxic Event (T-OAE) has been recorded, followed by a long-lived recovery of δ\(^{238}U\) values. This excursion represents a global expansion of marine anoxia of ~6 to 8% of the global seafloor during the peak of the T-OAE, which represents 28 to 38 times the extent of anoxia in the modern ocean. When compared with estimates of seafloor anoxic area for other CO2-driven global anoxic events, the T-OAE was the second-largest anoxic event of at least the last 300 My. As such, the T-OAE represents a powerful analog for future anthropogenic ocean deoxygenation.
Abstract
The Toarcian Oceanic Anoxic Event (T-OAE; ~183 Mya) was a globally significant carbon-cycle perturbation linked to widespread deposition of organic-rich sediments, massive volcanic CO2 release, marine faunal extinction, sea-level rise, a crisis in carbonate production related to ocean acidification, and elevated seawater temperatures. Despite recognition of the T-OAE as a potential analog for future ocean deoxygenation, current knowledge on the severity of global ocean anoxia is limited largely to studies of the trace element and isotopic composition of black shales, which are commonly affected by local processes. Here, we present the first carbonate-based uranium isotope (δ\(^{238}U\)) record of the T-OAE from open marine platform limestones of the southeastern Tethys Ocean as a proxy for global seawater redox conditions. A significant negative δ\(^{238}U\) excursion (~0.4‰) is recorded just prior to the onset of the negative carbon isotope excursion comprised within the T-OAE, followed by a long-lived recovery of δ\(^{238}U\) values, thus confirming that the T-OAE represents a global expansion of marine anoxia. Using a Bayesian inverse isotopic mass balance model, we estimate that anoxic waters covered ~6 to 8% of the global seafloor during the peak of the T-OAE, which represents 28 to 38 times the extent of anoxia in the modern ocean. These data, combined with δ\(^{238}U\)-based estimates of seafloor anoxic area for other CO2-driven Phanerozoic OAEs, suggest a common response of ocean anoxia to carbon release, thus improving prediction of future anthropogenically induced ocean deoxygenation.
Remírez, Mariano N.; Gilleaudeau, Geoffrey J.; Gan, Tian; Kipp, Michael A.; Tissot, François L. H.; Kaufman, Alan J.; Parente, Mariano
Carbonate uranium isotopes record global expansion of marine anoxia during the Toarcian Oceanic Anoxic Event
Proceedings of the National Academy of Sciences, 121(27) e2406032121; DOI: 10.1073/pnas.2406032121
© 2024 National Academy of Sciences.
Reprinted under the terms of s60 of the Copyright, Designs and Patents Act 1988.
Early Jurassic marine life
This event is known to have occurred during the Early Jurassic, so creationists' task is simple: Find out how the date of the Early Jurassic was calculated and explain why the technique(s) used were wrong by orders of magnitude that made 10,000 or less years just happen to look like 183 million years.
When they've done that, then they need to explain why such a volcano-driven environmental disaster, with very high temperatures due to global warming on a scale much more massive than what we are experiencing now, doesn't get so much as a hint in the Bible. Estimates put that increase to between 4 and 8 °C (currently we are facing a rise of 2 to 4 °C). Had there been humans around at the time, they would almost certainly have been part of the resulting mass extinction. Earth had suddenly become a very hostile place for anything living on it or in its oceans.
Creationists might also like to explain how these mass extinction events that punctuate the history of life on Earth fit in with the notion that Earth is fine-tuned for life.
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