Throughout Earth’s history, there have been five ‘wipe-out’ extinction events that have reset the clock on life.

This week on Show Me the Science, Professor Luke O’Neill explained what these events can teach us – and why scientists think we may be due for another soon.

Prof O’Neill said that there are five key types of evidence scientists use to determine if an extinction event has happened or not.

“The evidence is mainly in the fossil record,” he said.

“The other evidence is geological; you’ll see things in the rocks that are evidence for things going badly wrong.

“The big one I’ll mention is iridium, which I will come on to in a minute.

“There’s also, you can see things like what’s called shocked quartz.

“Many of these extinction events, or two or three of them, were asteroids hitting the Earth, and that gave rise to compression of quartz.”

D0RGDE Asteroid near Earth. Image shot 08/2012. Exact date unknown.

The fifth thing used to determine extinction events is isotopes.

“Some of the events, as I explained, were because oxygen levels fell,” Prof O’Neill said.

“They fell for various reasons, and much of life on Earth uses oxygen, so if oxygen goes, life then becomes extinct.

“You can see that in the rocks, when oxygen levels had fallen for a period.”

Climate change

According to Prof O’Neill, while the death of the dinosaurs is the most well-known extinction, not all events are so sudden.

“This one was around 375 million years ago, an asteroid hit the earth and that caused massive climate change,” he said.

“As I mentioned, the evidence is along the lines of quartz shock and various isotopes and so on.

“The reason for that is a huge amount of dust goes up, obscures the sun, and now the temperature begins to change.

“In particular plants are wiped out; that meant oxygen levels fall because plants are the source of oxygen, and now 75% of species are lost at that time and 25% survive.

“That’s the Late Devonian extinction event.”

Bothriolepis was a carnivorous marine fish that lived in the waters of the Devonian Seas. Image: Corey Ford. 10 February 2023

Prof O’Neill warned that this may not be the last climate-related extinction event.

“The example we have with the dinosaurs is a good one,” he said.

“If the plants die off, the herbivores die off, and now the carnivores die off – it's a knock-on effect.

“The indicator species that are dying off could predict further problems.

“Of course, it’s a bit hypothetical, it’s not as if it’s like the dinosaurs.

“But the evidence is growing that we are triggering another extinction event that might come.”

Main image: Luke O'Neill (L), dinosaur (R).