The extinction of the non-avian dinosaurs was nothing short of dramatic. An asteroid, 10 kilometers (6 miles) in diameter, slammed into the Yucatán Peninsula, creating a massive heat blast, generating vast tsunamis, and blanketing the sky with radioactive debris.
At the same time, a huge series of volcanic eruptions added more sunlight-blocking aerosols to Earth’s atmosphere, helping to drive the lumbering beasts of the Cretaceous into extinction. During this prolonged chaos and destruction, life in the oceans was also decimated: up to 95 percent of all marine species went extinct.
Researchers have long assumed that the asteroid impact, and the accompanying acid rainstorms, severed the food supply in the oceans by annihilating algae near the surface. Remarkable new research, published in the journal Geology, reveals that far more microscopic life survived the 66-million-year-old mass extinction event than previously thought.
“This provided a slow trickle of food for organisms living near the ocean floor which enabled them to survive the mass extinction, answering one of the outstanding questions that still remained regarding this period of history,” Heather Birch, a paleoclimatologist at Cardiff University and lead author of the research, said in a statement.
The plesiosaur was one of the many creatures that perished at the end of the Cretaceous. Esteban De Armas/Shutterstock
In the oceans, there exists something called the “biological pump.” Photosynthesizing algae at the surface absorb atmospheric carbon dioxide, before being consumed by predators. When these predators die, they sink down into the depths of the oceans, and eventually reach the seafloor.
The efficiency of the biological pump can be assessed by looking at how much carbon is found in the remains of creatures that have sunk into the sea. The more carbon, the more surface algae there were in the first place.
For this new study, sediment cores dating back to the time immediately following the Cretaceous extinction event were drilled and removed from the seafloor. Birch noticed that the chemical composition of the fossilized shells of marine animals contained a surprisingly high amount of carbon, meaning that despite the global devastation, the biological pump was still operating – albeit in a weakened state.
This meant that certain resilient species of algae still existed after the asteroid hit. This vital food source, much of which trickled down to creatures sheltering at depth, allowed a clutch of marine life to survive the apocalypse.
The team estimates that it took 1.7 million years for the biological pump to be restored to full strength, half the most commonly cited previous estimates. The implication is that marine life bounced back twice as fast as scientists previously thought.
The biological pump. National Oceanography Centre/U.S. JGOFS
The end-Cretaceous mass extinction, without a doubt, killed off a lot of life on Earth. Overall, up to 75 percent of life perished, including the non-avian dinosaurs, some mammals, the pterosaurs, insects, and plants. Within the oceans, giant marine lizards and the plesiosaurs died out, and a vast number of fish, sharks, mollusks, plankton and algae disappeared. Coral reefs didn’t return for 10 million years.
It’s remarkable in a way that life survived at all, but as this study shows, life finds a way. Even after the “Great Dying” – a 252-million-year-old mass extinction event that killed off over 90 percent of all life on Earth – a handful of organisms persisted, which eventually led to the rise of the dinosaurs.