02/05/2017 Battered Earth revived by mineral weathering after mass extinction

Massive volcanic eruptions occurred as the supercontinent Pangea started to split and crack. With eruptions fumes of greenhouse gases were released from the Earth's interior, causing catastrophic climate change Photo: Cai Tjeenk Willink/Wikimedia Commons

Bedrock of Earth got severely beaten up by hothouse climate conditions during one of planet’s mass extinctions some 200 million years ago. But the process also allowed life to bounce back.

Text: Maja Sojtaric

One of the Big Five mass extinction events occurred some 200 million years ago. Giant volcanic eruptions and an asteroid impact have been blamed for causing the disastrous change of climate, killing off nearly half of the species on Earth.  

The time epoch is called late Triassic. Amounts of carbon dioxide released through the volcanic activity during this time were staggering. Concentrations of CO2 in the atmosphere were up to 1000 ppm or so due to the volcanic activities of the period. For comparison, we have just recently reached 410 ppm of CO2 in the atmosphere today, a concentration that worries many scientists.

“In addition to the warming effects of the CO2 release, dissociation of massive amounts of methane hydrates had intensified the warming effect during the mass extinction. “ says Jochen Knies of CAGE and Geological Survey of Norway. He is a coauthor on recent Nature Communication study that has found evidence of impact of hothouse climate conditions of the late Triassic in Scandinavia.

Precisely dating deeply impacted bedrock

Published in Nature Communications by Ola Fredin (Geological Survey of Norway) and colleagues, these new findings shed light on how high greenhouse gas concentrations caused the bedrock to disintegrate through chemical weathering. Chemical weathering is caused by water reacting with the mineral grains in rocks to form new minerals, such as clay mineral illite. These reactions occur particularly when the water is acidic, as is the case when the CO2 levels are high.

Sampling site saprolite

Saprolite, is chemically weathered rock that scientists collected from several sites in Scandinavia, including this outcrop in Ivö, Sweden. Picture from paper.

“We have managed to precisely date deeply weathered crystalline bedrock from the North Sea and across Scandinavia, which then was part of the supercontinent Pangea. We did this by detailed geomorphological and mineralogical analyses of weathered rocks combined with the dating of clay mineral illite”, says Knies.

All the dated samples show that intensive and widespread chemical weathering occurred under hothouse conditions during the late Triassic. The bedrock was slowly transformed, and the transformation co-occurred with emerging volcanic activity.

Bedrock eventually removes CO2


Microscopic images of illite, a clay mineral that forms by chemical weathering of bedrock, found in a well in Norwegian offshore petroleum province Utsira High, North Sea. Picture from paper.

The hothouse conditions of this mass extinction caused oceans to eventually become depleted of oxygen, and thus become unbearable to live in. But weathering of silicate in the bedrock of Pangea, and subsequent formation of carbonate, tied up the CO2 into the minerals, slowly removing the greenhouse gas from the atmosphere.

“Transport of loose material towards the ocean may have stimulated both end of life through formation of oxygen-depleted waters as well as recovery of life through stabilization of the greenhouse effect through CO2 removal.” says Knies.

Reference: Ola Fredin et al. ( 2017) The inheritance of a Mesozoic landscape in western Scandinavia.  Nature Communications 8, doi:10.1038/ncomms14879


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