Antarctic marine life recovery following the dinosaurs’ extinction
A new study shows how marine life around Antarctica returned after the extinction event that wiped out the dinosaurs.
A team led by British Antarctic Survey studied just under 3000 marine fossils collected from Antarctica to understand how life on the sea floor recovered after the Cretaceous-Paleogene (K-Pg) mass extinction 66 million years ago. They reveal it took one million years for the marine ecosystem to return to pre-extinction levels. The results are published today (19 June 2019) in the journal Palaeontology.
The K-Pg extinction wiped out around 60% of the marine species around Antarctica, and 75% of species around the world. Victims of the extinction included the dinosaurs and the ammonites. It was caused by the impact of a 10 km asteroid on the Yucatán Peninsula, Mexico, and occurred during a time period when the Earth was experiencing environmental instability from a major volcanic episode. Rapid climate change, global darkness, and the collapse of food chains affected life all over the globe.
The K-Pg extinction fundamentally changed the evolutionary history of life on Earth. Most groups of animals that dominate modern ecosystems today, such as mammals, can trace the roots of their current success back to the aftermath of this extinction event.
A team of scientists from British Antarctic Survey, the University of New Mexico and the Geological Survey of Denmark & Greenland show that in Antarctica, for over 320,000 years after the extinction, only burrowing clams and snails dominated the Antarctic sea floor environment. It then took up to one million years for the number of species to recover to pre-extinction levels.
Author Dr Rowan Whittle, a palaeontologist at British Antarctic Survey says:
“This study gives us further evidence of how rapid environmental change can affect the evolution of life. Our results show a clear link in the timing of animal recovery and the recovery of Earth systems.”
Author Dr James Witts, a palaeontologist at University of New Mexico says:
“Our discovery shows the effects of the K-Pg extinction were truly global, and that even Antarctic ecosystems, where animals were adapted to environmental changes at high latitudes like seasonal changes in light and food supply, were affected for hundreds of thousands of years after the extinction event.”
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Plate tectonics may have driven ‘Cambrian Explosion’
The quest to discover what drove one of the most important evolutionary events in the history of life on Earth has taken a new, fascinating twist.
A team of scientists have given a fresh insight into what may have driven the “Cambrian Explosion” — a period of rapid expansion of different forms of animal life that occurred over 500 million years ago.
While a number of theories have been put forward to explain this landmark period, the most credible is that it was fuelled by a significant rise in oxygen levels which allowed a wide variety of animals to thrive.
The new study suggests that such a rise in oxygen levels was the result of extraordinary changes in global plate tectonics.
During the formation of the supercontinent ‘Gondwana’, there was a major increase in continental arc volcanism — chains of volcanoes often thousands of miles long formed where continental and oceanic tectonic plates collided. This in turn led to increased ‘degassing’ of CO2 from ancient, subducted sedimentary rocks.
This, the team calculated, led to an increase in atmospheric CO2and warming of the planet, which in turn amplified the weathering of continental rocks, which supplied the nutrient phosphorus to the ocean to drive photosynthesis and oxygen production.
The study was led by Josh Williams, who began the research as an MSc student at the University of Exeter and is now studying for a PhD at the University of Edinburgh.
During his MSc project he used a sophisticated biogeochemical model to make the first quantification of changes in atmospheric oxygen levels just prior to this explosion of life.
Co-author and project supervisor Professor Tim Lenton, from the University of Exeter’s Global Systems Institute said: “One of the great dilemmas originally recognised by Darwin is why complex life, in the form of fossil animals, appeared so abruptly in what is now known as the Cambrian explosion.
“Many studies have suggested this was linked to a rise in oxygen levels — but without a clear cause for such a rise, or any attempt to quantify it.”
Not only did the model predict a marked rise in oxygen levels due to changes in plate tectonic activity, but that rise in oxygen — to about a quarter of the level in today’s atmosphere — crossed the critical levels estimated to be needed by the animals seen in the Cambrian explosion.
Williams added: “What is particularly compelling about this research is that not only does the model predict a rise in oxygen to levels estimated to be necessary to support the large, mobile, predatory animal life of the Cambrian, but the model predictions also show strong agreement with existing geochemical evidence.”
“It is remarkable to think that our oldest animal ancestors — and therefore all of us — may owe our existence, in part, to an unusual episode of plate tectonics over half a billion years ago” said Professor Lenton.
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Materials provided by University of Exeter. Note: Content may be edited for style and length.