Fig. 2: Reconstruction of a marine landscape of the Early Pliocene (5.1-4.5 million years ago)
Art © Alberto Gennari.
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.
© CSIC - Daniel García-Castellanos.
What and when was the Messinian Salinity Crisis and what impact did it have on biodiversity in the Mediterranean? The Messinian Salinity Crisis (MSC was a geological event that occurred between approximately 5.96 and 5.33 million years ago during the late Miocene epoch. It was characterized by the near-complete desiccation (drying out) of the Mediterranean Sea due to a dramatic drop in sea level and the isolation of the Mediterranean from the Atlantic Ocean.How the MSC shaped the biodiversity of the Mediterranean is the subject of a paper just published in Science by an international team led by Konstantina Agiadi from the University of Vienna. Their research is explained in a Universität Wien press release:
Causes of the Messinian Salinity Crisis
The MSC was primarily caused by tectonic events, specifically the closure of the connections between the Mediterranean Sea and the Atlantic Ocean. This was largely due to the uplift of the Rif and Betic mountain ranges in present-day Morocco and Spain, which restricted water flow from the Atlantic into the Mediterranean. As a result, the Mediterranean's inflow of water from the Atlantic was significantly reduced or even stopped altogether at times.
Due to high evaporation rates and limited inflow, the Mediterranean Sea experienced extreme salinity levels, leading to the precipitation of vast amounts of salt and gypsum, which formed thick evaporite deposits on the seafloor. This process significantly lowered the sea level, and in some parts of the basin, the Mediterranean may have almost entirely dried up.
Impact on Biodiversity
The Messinian Salinity Crisis had profound impacts on biodiversity in the Mediterranean region:
End of the Crisis
- Marine Life: The extreme salinity levels and the reduction of marine habitats due to desiccation led to the mass extinction of many marine species. The Mediterranean became inhospitable to most marine life, drastically reducing biodiversity. Many endemic species of fish, mollusks, and other marine organisms were lost.
- Terrestrial and Coastal Ecosystems: The exposure of large areas of the seabed created new land bridges and altered coastal environments, which would have allowed the migration of terrestrial species and potentially the development of new habitats. However, the newly exposed land was likely barren and covered with salt flats, which were not conducive to supporting diverse ecosystems.
- Freshwater Species: Some freshwater and brackish environments may have formed in isolated pockets or lagoons, potentially allowing certain species to survive and adapt to the changing conditions. However, these habitats would have been limited and fragmented.
- Long-term Evolutionary Impact: After the crisis ended and the Mediterranean refilled rapidly during the Zanclean flood (when the Strait of Gibraltar reopened about 5.33 million years ago), new species began to colonize the Mediterranean from the Atlantic Ocean. This event allowed for a new phase of biodiversity development, but the pre-crisis biodiversity levels were never fully restored.
The MSC ended with the Zanclean flood when the Atlantic Ocean breached the barrier at the Strait of Gibraltar, rapidly refilling the Mediterranean basin. This event likely occurred over a relatively short geological time span, perhaps even as quickly as a few months to a couple of years, creating the Mediterranean Sea as we know it today.
In summary, the Messinian Salinity Crisis was a dramatic event that severely impacted the Mediterranean's biodiversity, causing significant extinction of marine life and altering terrestrial ecosystems. Its effects on biodiversity were long-lasting, influencing the evolutionary trajectories of many species in the region.
Are there any effects of this that can be seen today?
Yes, the Messinian Salinity Crisis (MSC) left several lasting effects that can still be observed today, both in the geological record and in the present-day geography and ecology of the Mediterranean region:
These enduring features provide a fascinating glimpse into the ancient past of the Mediterranean region and highlight the profound impact of the Messinian Salinity Crisis on Earth's geological and ecological history.
- Evaporite Deposits
One of the most significant legacies of the MSC is the extensive evaporite deposits that are found beneath the Mediterranean Sea. These deposits consist of thick layers of salt, gypsum, and other minerals that precipitated out of the water as the sea became increasingly saline. These evaporites can be up to several kilometers thick in places and are important for:
- Geological Studies: They provide valuable information about the MSC and help geologists understand past climatic and oceanographic conditions.
- Oil and Gas Exploration: The salt layers formed during the MSC act as cap rocks, trapping hydrocarbons beneath them. This makes the Mediterranean basin a significant area for oil and gas exploration.
- Submarine Canyons and Erosional Features
During the MSC, significant erosion occurred as rivers cut deep canyons into the exposed seabed, creating features that are still visible today:
- Submarine Canyons: These are deep, steep-sided valleys on the seabed that were carved by rivers and streams during the period when the Mediterranean was partially or nearly completely dry. Examples include the Nile and Rhone canyons, which extend far into the Mediterranean basin.
- Erosional Surfaces: The seabed shows evidence of massive erosion, with surfaces scoured by wind and water action during the MSC.
- Strait of Gibraltar and Atlantic-Mediterranean Connection
The Strait of Gibraltar, which was central to the refilling of the Mediterranean, remains a key feature that regulates the flow of water between the Atlantic Ocean and the Mediterranean Sea:
- Water Exchange: The narrow strait controls the exchange of water, temperature, and salinity between the Atlantic and Mediterranean. This unique exchange maintains the Mediterranean's higher salinity levels compared to the Atlantic, a consequence of the restricted flow that dates back to the MSC.
- Modern Biodiversity Patterns
The MSC had a lasting impact on the biodiversity of the Mediterranean:
- Species Composition: After the MSC ended, the Mediterranean Sea was recolonized primarily by species from the Atlantic Ocean. As a result, the Mediterranean’s current marine biodiversity is less diverse and more closely related to Atlantic species than it might have been if the MSC had not occurred.
- Endemic Species: Some species that adapted to the unique conditions post-MSC have become endemic to the Mediterranean, although overall biodiversity remains lower compared to other similar-sized seas.
- Sediment Layers and Geological Markers
Sediment cores from the Mediterranean reveal distinct layers corresponding to the MSC. These layers are rich in evaporites and often capped by a sharp transition to normal marine sediments deposited after the Zanclean flood:
- Stratigraphic Markers: The sediment layers serve as key markers for geologists studying the Miocene epoch and provide insights into the timing and processes of the MSC.
- Isostatic Adjustments and Seafloor Topography
The drastic loss and subsequent gain of water mass due to the MSC caused significant isostatic adjustments (changes in Earth's crust due to weight changes):
- Seafloor Subsidence and Uplift: The weight of the evaporite deposits and the water during refilling affected the seafloor’s shape, leading to subsidence in some areas and uplift in others, which has influenced the current topography of the Mediterranean basin.
Would it be true to say that biodiversity in the Mediterranean is the result of evolution over the past 5.5 million years or so, from species that came in from the Atlantic?
Yes, it is largely true to say that the biodiversity in the Mediterranean today has evolved over the past 5.5 million years, primarily from species that recolonized the basin from the Atlantic Ocean after the Messinian Salinity Crisis ended.
Key Points Supporting This:
- Recolonization After the Zanclean Flood:
- When the Strait of Gibraltar reopened around 5.33 million years ago, the Mediterranean was rapidly refilled with water from the Atlantic. This event, known as the Zanclean flood, allowed a massive influx of Atlantic marine species into the newly formed Mediterranean Sea.
- The rapid refilling and reconnection created a "reset" of the Mediterranean ecosystem, with the majority of the species that initially colonized the sea coming directly from the Atlantic Ocean.
- Evolution and Adaptation:
- Over the subsequent 5.5 million years, these Atlantic species underwent various evolutionary changes, adapting to the unique environmental conditions of the Mediterranean. This led to the development of new, often endemic, species—those found nowhere else in the world.
- Factors such as higher salinity, temperature variations, and unique habitat types in the Mediterranean drove evolutionary pressures, resulting in distinct adaptations and speciation.
- Lower Overall Biodiversity Compared to Pre-MSC:
- Before the MSC, the Mediterranean had a more diverse ecosystem with many endemic species that evolved over millions of years when the Mediterranean was a more stable environment. The MSC caused a major extinction event, significantly reducing this ancient biodiversity.
- The post-MSC Mediterranean has a somewhat less diverse marine ecosystem compared to other similar-sized bodies of water, primarily because it has had only about 5.5 million years to redevelop its biodiversity, starting mostly from a smaller pool of Atlantic colonizers.
- Present-Day Biodiversity Patterns:
- The modern Mediterranean Sea has a mix of species: those directly descended from Atlantic colonizers, species that have migrated more recently through human activity (such as via the Suez Canal, known as Lessepsian migration), and a number of newly evolved endemic species.
- The Mediterranean's biodiversity remains closely linked to the Atlantic but shows distinct differences due to the unique conditions of the sea, such as its higher salinity and temperature gradients.
Conclusion
Overall, the biodiversity of the Mediterranean is indeed a result of evolution over the past 5.5 million years, primarily involving species that originated from the Atlantic after the end of the Messinian Salinity Crisis. This evolutionary process has shaped the Mediterranean into a distinct but less diverse marine ecosystem compared to its pre-MSC state, highlighting the long-lasting impact of this ancient geological event.
How a salt giant radically reshaped Mediterranean marine biodiversitySadly, the body of this paper is behind an expensive paywall so only the abstract is available:
First quantification of a major ecological crisis and recovery
A new study paves the way to understanding biotic recovery after an ecological crisis in the Mediterranean Sea about 5.5 million years ago. An international team led by Konstantina Agiadi from the University of Vienna has now been able to quantify how marine biota was impacted by the salinization of the Mediterranean: Only 11 percent of the endemic species survived the crisis, and the biodiversity did not recover for at least another 1.7 million years. The study was just published in the renowned journal Science.
Lithospheric movements throughout Earth history have repeatedly led to the isolation of regional seas from the world ocean and to the massive accumulations of salt. Salt giants of thousands of cubic kilometers have been found by geologists in Europe, Australia, Siberia, the Middle East, and elsewhere. These salt accumulations present valuable natural resources and have been exploited from antiquity until today in mines around the world (e.g. at the Hallstatt mine in Austria or the Khewra Salt Mine in Pakistan).
The Mediterranean salt giant is a kilometer-thick layer of salt beneath the Mediterranean Sea, which was first discovered in the early 1970s. It formed about 5.5 million years ago because of the disconnection from the Atlantic during the Messinian Salinity Crisis. In a study published in the journal Science, an international team of researchers – comprising 29 scientists from 25 institutes across Europe – led by Konstantina Agiadi from University of Vienna now was able to quantify the loss of biodiversity in the Mediterranean Sea due to the Messinian crisis and the biotic recovery afterwards.
Fig. 1: Marine sediments hosting abundant fossils dated in the Late Miocene, from about 8 to 7 million years ago. Fish otoliths, bivalve and gastropod shells, bryozoans and microscopic shells attest to the presence of numerous organisms in this area, which have been analyzed in this study.© Konstantina Agiadi
Huge impact on marine biodiversity
After several decades of painstaking research on fossils dated from 12 to 3.6 million years found on land in the peri-Mediterranean countries and in deep-sea sediment cores, the team found that almost 67% of the marine species in the Mediterranean Sea after the crisis were different than those before the crisis. Only 86 of 779 endemic species (living exclusively in the Mediterranean before the crisis) survived the enormous change in living conditions after the separation from the Atlantic. The change in the configuration of the gateways, which led to the formation of the salt giant itself, resulted in abrupt salinity and temperature fluctuations, but also changed the migration pathways of marine organisms, the flow of larvae and plankton and disrupted central processes of the ecosystem. Due to these changes, a large proportion of the Mediterranean inhabitants of that time, such as tropical reef-building corals, died out. After the reconnection to the Atlantic and the invasion of new species like the Great White shark and oceanic dolphins, Mediterranean marine biodiversity presented a novel pattern, with the number of species decreasing from west to east, as it does today.
Recovery took longer than expected
Fig. 2: Reconstruction of a marine landscape of the Early Pliocene (5.1-4.5 million years ago) off the coast of Tuscany (central Italy) showing the monodontid Casatia thermophila and the sirenian Metaxytherium subapenninum - two of the many species that were only found in the Mediterranean Sea after the reopening of the gateway to the Atlantic.Art © Alberto Gennari.
Because peripheral seas like the Mediterranean are important biodiversity hotspots, it was very likely that the formation of salt giants throughout geologic history had a great impact, but it hadn’t been quantified up to now.
Our study now provides the first statistical analysis of such a major ecological crisis. The biodiversity in terms of number of species only recovered after more than 1.7 million years.
Konstantina Agiadi, lead author
Department of Geology
University of Vienna, Vienna, Austria.
Furthermore, it also quantifies for the first time the timescales of recovery after a marine environmental crisis, which is actually much longer than expected. The methods used in the study also provide a model connecting plate tectonics, the birth and death of the oceans, Salt, and marine Life that could be applied to other regions of the world.
The results open a bunch of new exciting questions. How and where did 11% of the species survive the salinization of the Mediterranean? How did previous, larger salt formations change the ecosystems and the Earth System?
Daniel García-Castellanos, senior author
Geosciences Barcelona (CSIC), Spain.
These questions are still to be explored, for instance also within the new Cost Action Network "SaltAges" starting in October, where researchers are invited to explore the social, biological and climatic impacts of salt ages.
Fig. 3: The end of the Messinian Salinity Crisis, ~5.3 million years ago, was marked by a distinct change in the sediments deposited on the Mediterranean Sea floor, which is seen here at Pissouri area, on Cyprus.© Konstantina Agiadi
Fig. 4: Konstantina Agiadi at the Laganas coast, on Zakynthos, Greece, where the end of the Messinian Salinity Crisis can be observed.© Konstantina Agiadi
Fig. 5: Cast of a bivalve shell preserved in 6.5-million year old sediment on Crete (Greece). The scientists analyzed the presences of organisms such as this to complete their extensive analysis.© Konstantina Agiadi
A short clip by France 5 on the Mediterranean salt giant (Messinian salinity crisis) - "Cataclysmes: le grandes régulateurs", a documentary by Christine Tournadre. Very happy of the final shape of the 3D animations. As real as they can get!
— Daniel García-Castellanos (@danigeos) May 6, 2022
1/2 pic.twitter.com/tvajbBJeVU
Original publication:Agiadi et al. (2024)
The marine biodiversity impact of the Late Miocene Mediterranean salinity crisis. Science. DOI: 10.1126/science.adp3703
AbstractThe teams concluding paragraphs of their paper at the end of the discussion section, is probably best ignored by creationists because it strongly contradicts their childishly parochial notion that Earth is perfectly designed for life. In fact, as the evidence shows, it is dynamic and has had periods where the environment has resulted in a mass extinction:
Massive salt accumulations, or salt giants, have formed in highly restricted marine basins throughout geological history, but their impact on biodiversity has been only patchily studied. The salt giant in the Mediterranean Sea formed as a result of the restriction of its gateway to the Atlantic during the Messinian Salinity Crisis (MSC) 5.97 to 5.33 million years ago. Here, we quantify the biodiversity changes associated with the MSC based on a compilation of the Mediterranean fossil record. We conclude that 86 endemic species of the 2006 pre-MSC marine species survived the crisis, and that the present eastward-decreasing richness gradient in the Mediterranean was established after the MSC.
The extraction of salt from the global ocean during the formation of salt giants may have affected the evolution of marine life through the effects of global ocean salinity on climate, ocean pH, and oxygenation (58–60). Hay et al. (61) postulated a correlation between the formation of the Mesozoic salt giants and the expansion of planktic foraminifera and calcareous nannoplankton into the open ocean, as well as a link between the Permian extraction of salt from the oceans and the end-Permian mass extinction (251.9 Ma). Although the evolution of planktic foraminifera lineages has been broadly associated with salinity reduction in the global ocean in the Late Miocene–Early Pliocene (62), this conclusion is contested because diversification can also be attributed to cooling climate (63). By contrast, there is a clear link between salt giant formation and the end-Triassic mass extinction (201.4 Ma): Evaporite deposition removed sulfate from the ocean just before periods of increased volcanic activity, which facilitated large-scale oceanic anoxic events during hyperthermal events that led to the mass extinction (59).Since the underlying cause of these events is plate tectonics, which continues today much as it did 5.5 million years ago, creationists can't honestly claim that their putative designer god decided to make Earth perfectly tuned for life just a few thousand years ago. In fact, the same geological events that caused these sudden changes that resulted in mass extinctions, followed by renewed diversification, are still happening and are capable of turning Earth's fragile ecosystems into extremely hostile places.
Salinity crises have occurred repeatedly throughout geologic history in restricted evaporitic basins controlled by dynamic marine gateways that result from the formation and demise of oceans by tectonic motions and sea-level changes (64, 65). Globally, at least 138 evaporitic basins have occurred from the Proterozoic until the Miocene (66). The Mediterranean salt giant is one of the most recent among the salt giants of the Neoproterozoic (Australia), Paleozoic (Siberia, United States, and northwestern Europe), Mesozoic (the Gulf of Mexico and the South Atlantic off of Brazil, Angola, and Gabon), and the Early (Iran), Middle (Red Sea), and Late Miocene (eastern Europe) (64). In terms of size, the amount of salt (halite) deposited in the Mediterranean during the MSC was smaller than those salt giants reported from the Early Cretaceous and the Middle to Late Jurassic (61). However, the way in which the MSC reshaped Mediterranean ecosystems provides a precise quantification of biotic recovery from ecological crises. Transferring our model (Fig. 3) to other salt giants will lead to adjustments in regional geographic, geologic, oceanographic, and climatic frameworks.
The child-like, stary-eyed belief that somehow Earth is perfectly designed by a perfect, omnibenevolent god, is a delusion that depends on an almost complete ignorance of reality, as is the childish delusion that it was all created out of nothing by magic, just for humans, a few thousand years ago.
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