Surviving mass extinction
Horseshoe crabs and their relatives (xiphosurids) have existed for at least 445 million years. They have survived at least 4 mass extinction events. © stockicide, CC-BY-2.0
Even after a major extinction event, life bounces back. Over time life finds new ways to live, and new species fill the gaps left by those that died out. Each of Earth’s mass extinctions was followed by a burst of evolution, albeit often after a fallow period that lasted over a million years.
What causes mass extinctions?
The evidence suggests there was no single cause for any of the mass extinctions in Earth’s history. Instead, a combination of factors created environmental changes that were so extreme they spelt disaster for all but a small number of lucky survivors.
Massive volcanic eruptions, shifting tectonic plates and asteroid impacts are leading culprits for many of the mass extinctions. They can create huge changes to climate, sea levels and the amount of oxygen in the oceans.
Life after a mass extinction
Species that survive find a new world waiting for them. Predators that once held their numbers in check might have disappeared, and competition for food and resources might have been reduced.
The mass extinction survivors and their descendants are able to experiment with different ways of living, adapting to the new circumstances they find themselves in. Life can evolve in new and strange ways.
Usually it takes several million years for life to recover from the battering of a mass extinction. Numbers need to be replenished and the environment may need to settle. After the particularly devastating end-Permian mass extinction it took 10-20 million years.
Are some species more likely to survive?
Larger animals tend to suffer the most in mass extinctions because they usually have specialised diet and habitat requirements. Plants are hardier.
There are some traits that can make species more likely to survive. Having a large population spread far and wide can give species a better chance of finding a place of refuge. And having a varied diet may be advantageous if some food sources disappear. Being small can also help as less food is needed to survive, while a high reproduction rate allows species to adapt more quickly to changes in their environment.
However, species with these traits can still become extinct. If all their populations live in an area struck by a huge meteorite or near a volcanic eruption then it might just come down to bad luck.
