Happy new year! This week we'll learn about the oldest mass extinction event, some 450 million years ago, and also sea scorpions. Further reading: Coming up for air: Extinct sea scorpions could breathe out of water, fossil detective unveils Sea scorpions could get really, really big: A fossil Eurypterus: Show transcript: Welcome to Strange Animals Podcast. I’m your host, Kate Shaw. Hello, 2021, please be better than 2020 was. I’ve got lots of fun, interesting episodes planned for this year, but let’s start the year off right with an episode about, uh, a major extinction event. Specifically it’s the Late Ordovician mass extinction, which occurred around 450 million years ago. This is the first of a series of episodes about extinction events I have planned for this year, which I hope you’ll find interesting. We’ll also learn about an animal called the sea scorpion. If you’ve listened to episode 69, about the Cambrian explosion, you may remember that the fossil record shows that around 540 million years ago life on earth evolved from simple organisms into much more complicated ones. This happened relatively quickly in geologic terms, about 15 to 25 million years for life to go from microbial mats, simple worms, and single-celled animals to fantastical creatures with shells and spikes and novel ways of feeding as animals adapted to fit new ecological niches. But what happened after that? A series of extinction events, that’s what. The first extinction event researchers can identify from the fossil record is called the End-Botomian extinction event, which happened around 510 million years ago in two phases. We’re not sure what caused the extinctions, but the main theory is that a series of massive volcanic eruptions caused climate changes that led to acidification of the oceans and a resulting loss of oxygen from the water. This was followed by another extinction event around 500 million years ago. All told, during these ten million years or so, about 40% of all species of animal went extinct. But remember, all we have to work with is the fossil record. Researchers know how old particular rock strata are, strata being the term for layers, so when they find a fossil embedded in a rock they know roughly how long ago it lived. Only a small percentage of animals that ever live end up fossilized, and only a small percentage of fossils are ever found by humans, and only a small percentage of fossils found by humans get studied by experts. So while scientists do their best, they’re working with a limited amount of data to determine what happened half a billion years ago. It’s like trying to determine the rise and fall of empires from a series of random photographs. But when older rocks show a whole lot of fossils of various kinds, and then slightly younger rocks show way fewer or no fossils, researchers can be pretty sure that something catastrophic happened to kill off a lot of animal life in a relatively short amount of time. If they find the same changes in rocks of the same age in different parts of the world, the catastrophe was probably worldwide and serious enough to impact life on Earth for thousands or even millions of years. That’s what happened in the late Ordovician. Around 460 million years ago, about the time that life was getting back to normal after the last extinction event, glaciers started to form across the land. Most of the continents at this time were smushed together into a supercontinent called Gondwana, which was mostly in the southern hemisphere. Much of the rest of the Earth was one big ocean, and it was hot and tropical just about everywhere. But that changed when temperatures dropped drastically. Glaciers formed, sea levels fell, and some 60% of all life on Earth went extinct, all possibly within about one million years. We don’t know why, but we do have some clues and some theories. We know there was a major meteor event around 467 million years ago,