What led to the extinction of dinosaurs? A big asteroid slammed into Earth 65 million years ago, darkening the sky and killing a large number of species, including dinosaurs. However, some animals, including mammals such as, crocodiles, birds, and turtles, managed to live. Despite being shrouded in death, the disaster aided the emergence of mammal. This resulted in a massive increase in their diversity and number.
Similarly, the world witnessed the worst mass extinction event in history 250 million years ago: the End-Permian Extinction. The catastrophe, also known as the Great Dying, was triggered by a series of volcanic eruptions. This also killed three-quarters of all land animals and even more in the waters. But, once again, some creatures managed to live.
A mystery connects these two events: why do certain animals perish while others survive huge extinctions? Two different teams looked at these two extinction events recently to see what allows a species to live when the world around them is dying.
Extinction of dinosaurs
We start in North Dakota’s Tanis region to learn about the extinction event that wiped off the dinosaurs 65 million years ago.
The poor fish in this estuary died an awful death 65 million years ago. Massive seismic waves buffeted the Yucatan peninsula just 10 minutes after the Chicxulub asteroid struck, severely rocking the ocean.
It showered down like devastating downpour on the Earth. The presence of spherules in the gills of the fish suggested that they were alive at the time the spherules invaded their bodies.
Emeritus Professor Jan Smit gave a talk in 2017 about his life’s work, which includes studies on these fish. Melanie During, a PhD student at Uppsala University, was immediately drawn to this. During told Big Think, “I emailed Jan.” “I told him that if they have fish that chronicle the final years of the Cretaceous — commonly known as the ‘gap’ since there are so few records of this time — we could use isotope analysis to reconstruct the end of the Cretaceous.”
During this time, he journeyed to the Tanis region and collected specimens. This included paddlefish jawbones and sturgeon pectoral fin spines.
“I chose these bones because I’d learnt that they developed in a similar way to trees. It added a new layer every year without remodeling,” During explained to Big Think.
During’s team was able to reconstruct the last moments of these fish’s life because they perished so quickly following the impact. They were able to discover that these fish perished in the Northern Hemisphere’s springtime by studying “rings” produced each season within their bones.
Although it’s too soon to come to any conclusions, this could provide insight into why some creatures perished while others thrived. Spring is a season of birth, reproduction, and growth. When you combine this with particular gestational dates, you can see how this asteroid came at the right time to kill these animals. Animals in the Southern Hemisphere, on the other hand, would have been preparing for wintertime. They might have been able to live if they had prepared for a cold season. Indeed, based on what has been observed thus far, wildlife in the Southern Hemisphere appear to have recovered twice as quickly as their counterparts in the Northern Hemisphere.
Although the extinction catastrophe that wiped off the dinosaurs is the most well-known, it wasn’t the deadliest. The End-Permian extinction event killed 75 percent of land-based animals and 90 percent of those in the waters 250 million years ago. In fact, it came dangerously close to putting an end to life on Earth.
Heavy volcanic activity in Siberia triggered it. The release of greenhouse gases resulted in a dramatic shift in climate, with the planet’s temperature rising by 10 degrees Celsius. But, once again, some species lived while others died.
A team led by Dr. William Foster used machine learning to look at similarities in species that survived.
The researchers looked at over 25,000 fossilized remains from South China, including algae, bivalves, sponges, and snails. Their machine learning programme was able to figure out what elements made a species more likely to become extinct.
One aspect that contributed to creatures’ survival rate was where they lived inside the water column. The increase in temperature in the shallow ocean would have been lethal to organisms, especially those that were already living in water that was on the higher end of their preferred temperature range. The decrease in dissolved oxygen deep within the water was the deciding factor. Mobile organisms, on the other hand, were able to travel to a more hospitable depth or position and survive.
Sometimes an animal’s survival depended solely on the type of shell it possessed. An example is brachiopods. “Brachiopods with apatite instead of calcite in their shell were less likely to become extinct,” Foster told Big Think. “We believe this is due to the fact that brachiopods with calcite shells are more vulnerable to ocean acidification.” This pattern persisted in other species as well.
Species having a lot of genetic variation within them fared better in the long run, maybe because they were more adaptable to environmental changes.
These machine learning approaches can even be used today to predict which species are more likely to become extinct in other extinction events.