Ancient rocks reveal climate disaster 200 million years ago

Ancient rock layers show how massive volcanic eruptions triggered rapid climate change and a mass extinction 200 million years ago, KVF reports. Faroese geologist Heiðrikur í Garði Mortensen has studied chemical traces in the layers to determine how quickly the climate changed and how long nature took to recover.

During the Jurassic period, Earth looked very different. Most of the continents were joined in a vast supercontinent called Pangea, and the Atlantic Ocean did not yet exist. Around this time, Pangea began to break apart, Heiðrikur said in the KVF programme Vitan.

Hot material from inside the Earth pushed beneath the crust, causing it to heat up, thin and split. Huge quantities of molten lava erupted through the cracks in volcanic activity known as the Central Atlantic Magmatic Province, or CAMP.

The eruptions helped create the continents and Atlantic Ocean as they are known today. They also triggered one of the five largest mass extinctions in Earth’s history.

A world of reptiles and ferns

Before the eruptions, animal and plant life was very different from today. Flowering plants did not exist. Coniferous trees and ferns grew in the forests, while reptiles and ammonites, an extinct group of shelled animals, lived in the oceans.

Dinosaurs already existed 200 million years ago, but they were only a small part of a much more diverse animal world, Heiðrikur said. Before the mass extinction, a crocodile-like group known as archosaurs dominated the land.

The major changes in ecosystems caused many animal groups to die out, creating better living conditions for other species. This was when dinosaurs found an ecological niche in which they could grow larger, he said.

Over just a few thousand years, which is a very short period in geological terms, the eruptions released enormous quantities of carbon dioxide and other substances into the atmosphere.

Global average temperatures rose by between five and 10 degrees. There was no ice at the poles. In the interior of Pangea, areas far from the sea became extremely dry, while other places experienced violent storms and exceptionally heavy rainfall, several times more intense than anything seen today.

The high temperatures also caused extensive forest fires. Ash and other particles from the fires ended up in the oceans, and the sedimentary rocks show that there were very large numbers of forest fires at the time, Heiðrikur said.

The abrupt climate change caused about 70 to 80 percent of animal species on land and in the oceans to die out.

Sedimentary rocks preserve climate records

Researchers cannot use direct temperature measurements from 200 million years ago. Instead, they use what is known as a proxy, an indirect measure of past climate, forest fires or volcanic activity.

Sedimentary rocks function like an archive for geologists and can reveal what the climate was like at the time, Heiðrikur said.

There are no sedimentary rocks from this period in the Faroe Islands because the islands did not yet exist. The Faroes formed much later, about 55 to 60 million years ago, when Greenland and Norway moved apart and the North Atlantic Ocean was created.

Heiðrikur therefore travelled abroad, including to Portugal and Austria, where sedimentary rocks dating back 200 million years can be found.

A new chemical fingerprint

Researchers have in recent years measured mercury in sedimentary rocks as evidence of volcanic eruptions. Volcanoes release mercury high into the atmosphere, where it is carried around the globe before settling in lakes and oceans.

Mercury is not a precise measure, however, because it can bind to organic material or be affected by other conditions. Heiðrikur has therefore helped develop a considerably more accurate method based on measurements of platinum-group elements, including platinum, palladium, ruthenium and iridium.

The elements are measured using advanced technology known as MC-ICP-MS at Aarhus University.