Why did trilobites go extinct?

Have you ever wondered why trilobites went extinct? It seems a bit baffling, to be honest. After all, trilobites were highly successful as an organism – at one time they were the dominant life form of the marine biosphere.

And no, humans were not responsible for their demise. We were millions of years away.

However, the exact cause for the trilobites' extinction is rather muddled. Several significant events were occurring millions of years immediately preceding their disappearance. Volcanoes were erupting, superbugs were flexing, a megacontinent was in the works, and the weather was fluctuating with wild abandon. To what degree did each of these contribute?

Ultimately, trilobites faded off the planet during "The Great Dying" of the Permian Extinction that decimated more than 90 percent of the earth's marine life 250 million years ago. It was the largest such event ever seen on earth, and even the wily trilobites couldn't withstand it.

Volcanoes and trilobite extinction

Picture this: it's a bleak winter Sunday morning, 240 million years ago, and several massive volcanoes over in Siberia have been erupting for, oh, about a hundred thousand years now. What can that possibly have to do with trilobites in oceans around the world? Well, a huge contributory factor could be that these volcanoes produced lava that covered almost three million square miles.

You see, scientists discovered a weird anomaly back in 2017. They measured high concentrations of the rare metal nickel in soil from the North Pole to India corresponding to the time frame of the Great Permian Extinction. Guess where you find high levels of nickel? The richest sources are cooled rocks from volcanic magma. The best explanation for this widespread presence of nickel is that the volcanoes in Siberia had a global influence.

Volcanic activity, however, does not kill globally with hot lava. It's the gases and the ash that dramatically affect worldwide climate, causing extreme cooling events by blocking the sun, and dramatic heating via trapped greenhouse gases. Those gases come from widespread forest fires caused by the lava, chemical reactions, and even direct emission from the mouth of the volcano.

You have to feel for the trilobites, and every other living thing on Earth. Things were tough out there.

Scientists believe lava reacted with coal that was already present in the soil. You already know what burning coal does to the atmosphere. The reaction produced methane and carbon monoxide gases on a massive scale, perhaps cooking the planet but depleting the oceans of oxygen.

It turns out trilobites needed oxygen, but that is not all they had to contend with.

Bacteria and trilobite extinction

New theories suggest volcanoes are not enough to explain global warming to an extent that would kill off almost all life on Earth. A newer study suggested that a type of nickel-eating bacteria increased exponentially when mineral deposits from the Siberian eruptions ended up in the oceans. Despite their tiny size, huge numbers of aerobic organisms consumed massive amounts of oxygen during metabolism. They then released methane and carbon dioxide, compounding climate change that may have been started by other catastrophic events. Moreover, carbon dioxide poisoning can stagnate ocean currents, further sustaining deadly levels of bacteria.

More bad news for the trilobites.

Ongoing climatic shifts

The end of the Permian Age wiped out the trilobites for good, but it wasn't the first existential blow to this unique collection of arthropods.

Here's a brief history of the trilobites and their abundance, and some of the things they had to deal with until being finally overwhelemed in the Permian.

Early Cambrian era - About 543 million years ago, the earth was a paradise for trilobites. They could bask in shallow waters, and ruled the sea with their remarkable ability to evolve rapidly.
Ordovician era - Who knew mountains could grow? In the last million years of the Ordovician age, about 440 million years ago, the planet suffered a severe ice age. It is thought to have been brought on by the rising Appalachian mountains. As more rock was exposed, the silicate attracted carbon dioxide, sucking away the earth's warmth. Trilobites adapted but huge numbers of them were still wiped out.
Silurian period - About 430 million years ago the trilobites regrouped. They had survived one major extinction but were going forward with lower numbers.
Devonian era - 359 years ago saw another massive extinction event associated with two things, episodes of global cooling and ocean anoxia. The former was brought on by organic sedimentation from an explosion in the numbers of terrestrial plants, the latter by global warming events. Several families of trilobites were decimated, especially those who'd adapted to shallow waters, thanks to glaciation and plummeting sea levels.
Early Permian period -
An estimated 290 million years ago, another ice age was exacerbated by the formation of Pangea. Some scientists believe this "supercontinent" caused the earth to cool by blocking usual ocean currents. This disruption may also have caused stagnation of the oceans.
Late Permian period - Uh-oh. Serious crunch time for our pals the trilobites. Volcanic eruptions in the Siberian traps likely caused episodic extremes in global warming and cooling. It is the worst extinction event known to have ever occurred on Earth. It destroyed, among much else, the very last families of trilobites. Lack of oxygen in the ocean was the direct cause of trilobite extinction. Whether it resulted from global warming, planetary cooling, or volcano or meteorite-induced acid rain remains unclear.

The gradual decline of trilobites over millions of years ensured they would not survive the Permian extinction crisis. But they had a great run. And their beautiful fossils exist in their millions for us to collect, admire, and study.

Why did trilobites go extinct?

Volcanoes and trilobite extinction

Bacteria and trilobite extinction

Ongoing climatic shifts

Links

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