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  • Writer's pictureSven Piper

The History of the Earth - Mass Extinction

Updated: 7 days ago

Artistic representation of a gamma ray burst
Artistic representation of a gamma ray burst (Credit: ESO)

The Earth has experienced numerous catastrophic events throughout its history, leading to mass extinctions where the majority of living creatures perished. In this special, we aim to provide an understanding of Earth's history and explore possible causes for these mass extinctions.

Over 4.5 billion years have passed since our solar system and Earth formed from a hydrogen cloud. It took about 500 million years for the first living creatures to emerge during the Archean era, when the primordial oceans formed and an oxygen-rich atmosphere developed, allowing for the formation of archaeobacteria.

It was not until 2.5 billion years ago, in the Proterozoic era, that unicellular bacteria evolved into multicellular organisms. Almost another 2 billion years passed before the Cambrian Explosion occurred 542 million years ago, marking a rapid diversification of life on Earth.

About 100 million years later, during the Silurian period of the Phanerozoic eon, the first vertebrates developed in water and later on land. It’s worth noting that invertebrates such as large cephalopods, which include squids, formed much earlier.

However, a significant event occurred earlier during the Ordovician period, 428 million years ago—the first mass extinction in Earth's history. Approximately 50-60% of all living organisms died out, with many trilobite species disappearing. Trilobites, crucial to paleontologists, lived from the Cambrian to the Permian periods, becoming extinct before the dinosaurs evolved.

More on this later, as life faced further setbacks during the Devonian period around 367 million years ago, with many species becoming extinct. Unfortunately, the exact circumstances of this mass extinction are no longer reconstructable, and while several theories exist, they are difficult to prove definitively.

Common causes of mass extinctions on Earth include meteorite impacts, supernova radiation, or gamma ray bursts (potentially the birth screams of black holes), and extreme volcanism.

A meteorite impact typically leaves clear traces, such as a large crater. However, if the impacting body is too large, it might penetrate the Earth’s crust or cause such a significant shockwave that any resulting crater could be refilled by magma, according to Newton's third law (action equals reaction). Fortunately, craters are not the only evidence of meteorite impacts. Such events also distribute large amounts of shattered quartz and the rare metal iridium—common in meteors—across the globe.

A gamma ray burst destroys the earth's atmosphere
A gamma ray burst destroys the earth's atmosphere (Credit: NASA)

The theory that a gamma ray burst could cause a mass extinction is relatively new, but according to NASA [1] and scientists at the University of Kansas, it's a plausible explanation for the Ordovician mass extinction. Such a burst would destroy Earth's ozone layer within seconds, allowing harmful UV radiation to penetrate the surface for years, severely damaging living cells and potentially causing widespread extinctions, including in the marine food chain due to the destruction of surface-dwelling plankton.

The idea that volcanism can lead to mass extinction might seem far-fetched at first. However, supereruptions, like those that could occur at Yellowstone, would have global effects similar to those of a large meteorite impact, including global dimming and climate change.

At the end of the Permian period, the largest mass extinction in the history of our planet took place. Seventy percent of all land dwellers and almost ninety-five percent of all aquatic life died out, and for a long time, the cause was a mystery to scientists as various possibilities were considered. The mystery began to unravel when thousands of kilometers of solidified lava were discovered under the snow and ice in Siberia, caused by gigantic volcanic eruptions (also known as the “Siberian Traps”) around 250 million years ago, which set hundreds of thousands of square kilometers ablaze. However, these volcanic eruptions were only the trigger for an even greater catastrophe. Rock analyses from Greenland revealed that the mass extinction occurred in three different phases: it began on land, where some plant and animal species disappeared within 40,000 years; then a massive extinction took place in the sea within just 5,000 years; and only then, in phase III, was there a major mass extinction on land, which lasted around 35,000 years.

The reason for this was that global temperatures, including sea temperatures, rose by around 5°C due to massive volcanism. This caused large quantities of methane hydrate, stored in a frozen state under the seabed, to thaw, releasing vast amounts of C-12 (carbon 12) and methane. Since methane is one of the most potent greenhouse gases, it led to an additional increase in global temperatures by 5°C.

A total increase in global temperatures of 10°C was therefore sufficient to trigger the worst mass extinction in history, a crucial consideration when discussing climate change.

Skeleton of a T-Rex
Skeleton of a T-Rex

Forty million years later (around 213 million years ago), at the end of the Triassic period, the next mass extinction occurred, which might have had a similar cause to the Permian extinction.

However, 65 million years ago, at the end of the Cretaceous period, an event occurred that left numerous traces and evidence. The vast majority of scientists believe that the dinosaurs were wiped out by a meteorite impact in the Gulf of Mexico or the Yucatan Peninsula, known as the Chicxulub Crater.

While some scientists support other theories, it is hard to dismiss a crater 180 kilometers wide—especially as there is now evidence that the crater is much larger than previously thought and also has a fourth outer ring. Nevertheless, it cannot be ruled out that a combination of factors contributed to the demise of the dinosaurs, as evidence of significant Deccan Traps volcanism has been found in India. The distribution of chromium isotopes from that time provides clear evidence of an extraterrestrial event, especially as this is the only way to explain the iridium anomaly from that era.

What did Earth look like at that time?

It is believed that the supercontinent Pangaea broke apart during the Mesozoic era, and the outlines of today's continents had already formed in the Cretaceous period. Additionally, there was already vegetation similar to today's, including deciduous trees like maple, oak, or walnut, and conifers.

Did all dinosaurs die out at the end of the Cretaceous period?

That's a good question, and until 2002, most scientists would have answered "yes." However, that year, in New Mexico, USA, leg bones of a hadrosaur were found that were clearly from the Cenozoic era and therefore at least 500,000 years younger. Unless water carried them into younger deposits, this suggests that a small population of dinosaurs survived for quite some time.

The final conclusion is that life on Earth has endured considerable challenges, and the next global catastrophe is inevitable. The question is not if it will occur, but when?

According to scientists Robert Rohde and Richard Muller from the University of California in Berkeley, mass extinctions on Earth follow a mysterious rhythm, occurring every 62 million years (±3 million years). According to Muller, this may be related to "astronomy," namely the orbit of the sun around the center of the galaxy, during which our solar system comes close to massive objects that could disrupt our outer solar system and potentially send comets on a collision course with Earth.

Note: You can find out a lot more about this topic in my book 'Exoplaneten - Die Suche nach einer zweiten Erde,' which is in German.

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