Here's a fun fact to use at your next Zoom party: 99.9% of all life that has ever existed on earth is now extinct. We are the 0.1%!
The fossilized remains of a past extinction event. Photo by Curtis MacNewton on Unsplash. Click for link.
The extinction of the dinosaurs is overrated.
Every kid has a dinosaur phase, where they can proudly name every dinosaur, and then tell you their favorite. I had a particularly pretentious dinosaur phase, where I repeatedly told friends that an Allosaurus was more dangerous than a Tyrannosaurus rex. During my dinosaur phase, I also remember my parents, in an attempt to teach their young children how to properly manage money, taking my brother and me to open a bank account. Instead of being impressed by the interest my $20 savings account would accrue, I latched onto the free dinosaur the banker gave us, forgetting about adulthood in the haze of having a new dinosaur.
There’s a reason every kid has a dinosaur phase, beyond the fact that dinosaurs are just cool. The extinction of the dinosaurs was dramatic, with a massive comet falling from the sky, releasing 2 million times more energy than a nuclear bomb. Wildfires spread across the planet, and the ash fall killed many of the plants. All of the dinosaurs, except a few stragglers, died out.
But this comet-induced mass extinction was actually the fifth mass extinction earth has faced.
The first mass extinction occurred around 440 million years ago. This first extinction, the Ordovician-Silurian extinction, is my favorite (if one is allowed to have a favorite mass extinction). Extinctions are named for the geological boundaries that occur before and after them. The first mass extinction is named the Ordovician-Silurian extinction because it ended the Ordovician period and started the Silurian period. Almost all life on earth lived in the ocean at this time. If you thought dinosaurs were cool, wait until you meet the animals of the Ordovician.
Truly strange creatures roamed the Ordovician seas. The Ordovician oceans were dominated by invertebrates (animals without spines); there were very few fish in the sea. Trilobites, tiny shelled creatures with many small legs and armored bodies, scuttled along the ocean floor. Trilobites were incredibly numerous, and ruled the oceans. Ocean predators, such as Cameroceras and Megalograptus, also formed part of the Ordovician food chain. Cameroceras, essentially a 2 m long shelled squid, prowled the seas. This ancient squid was the apex predator of the Ordovician. “Sea scorpions” such as Megalograptus, which were about 2.5 ft. long with long, spiny claws, swam through the oceans, competing with Cameroceras for prey (you are welcome for the nightmares). Gentle sea sponges swayed in the ocean currents, and they, along with early corals, created new habitats for Ordovician creatures.
The latest star of my nightmares: Megalograptus, the giant sea scorpion of the Ordovician. Creative Commons Ryan Somma. cc-by-sa-2.0. Click for link.
Besides the alien-looking species of the Ordovician ocean, the climate of the Ordovician earth was also vastly different from that of today. The Ordovician began around 485 million years ago with a “hothouse” earth, so called because there were no glaciers present on earth at this time. At the beginning of the Ordovician, ocean temperatures reached a high of 110°F, which is roughly 40° warmer than our current tropical oceans. The climate then gradually cooled for about the next 40 million years. But this cooling lead to disaster by the end of the Ordovician, with the formation of glaciers shrinking ocean levels, reducing the amount of habitat available for the diverse marine life. The cooler temperatures also killed many warm-adapted species.
The peaceful trilobite, ruler of the Ordovician seas. Creative commons Tim Evanson, cc by-sa 2.0. Click for link.
Some sources will dismiss the Ordovician-Silurian extinction with a simple “small marine organisms died out,” but this extinction resulted in about 86% of all life on earth going extinct. For comparison, the comet that killed the dinosaurs wiped out an estimated 60–76% of all life on earth. The Ordovician-Silurian extinction is the actually the second largest extinction earth has ever faced.
We are now giving the Ordovician-Silurian extinction a run for its money with what some researchers say is beginning of a sixth mass extinction. We are losing species at an unprecedented rate. In the last 400 years, about 800 species have gone extinct. A global 2019 report estimates that 1 million species are now threatened by extinction, mostly from human-caused climate change and other human impacts, such as deforestation and pollution. This sixth extinction could be devastating to all life on earth.
Our possible sixth extinction looks more like the Ordovician-Silurian extinction than the comet-induced extinction of the dinosaurs. There are no comets raining down on us; no ash filling our lungs. There is only the creeping realization that we are losing species, and the fight to keep what we species we can. The dinosaurs, with their death from above, might get all the attention. But the small fossilized trilobites are here to remind us of when they ruled the earth, and that not all mass extinctions come from the sky.
Rachel Sales is a Ph.D student, studying paleoecology. Find out more about her research here.