Europe burned for 30,000 years – ferns took over

 

Roland Johansson/TT

 

Published 05:55

          

         The forests of Europe were wiped out in huge fires at the end of the Triassic period 201 million                   years ago. Instead, the vegetation was dominated by ferns for hundreds of thousands of years.                     Photo: Image: Mark Garlick/TT

201 million years ago, the world suffered a major catastrophe when huge amounts of carbon dioxide were released into the atmosphere. As a result, Europe burned for 30,000 years and the forests were replaced by a savanna of ferns, according to a new study.

The catastrophe, which marks the end of the Triassic period, led to one of the worst mass extinctions to affect life on Earth. Approximately 75 percent of all species were wiped out.

The triggering factor was the separation of the North American and African continental plates and the beginning of the formation of the Atlantic Ocean. A series of cracks in the Earth's crust occurred, triggering huge volcanic eruptions and an unprecedented flow of lava. About 100,000 gigatons (100,000 billion tons) of carbon dioxide were released into the atmosphere – an unimaginable amount.

– The temperature rose by up to four degrees on Earth. It became much warmer than before the disaster and much warmer than today, says Sylvain Richoz, a geologist at Lund University and co-author of the study, which is published in Nature Geoscience.

Fires for thousands of years

The result was huge forest fires. According to Sylvain Richoz, the fires raged in Europe for about 30,000 years.

– Large parts of the entire Earth probably burned, but we don't know for sure, he says.

When the forests were wiped out, they were replaced by ferns that came to dominate the vegetation for a very long time – a strange type of savannah that has no equivalent in today's world. These were also fire-resistant, which meant that the fires returned at frequent intervals.

“Some trees survived, but only in small pockets in the landscape,” says Richoz.

A world of ferns

The ferns continued to dominate even after the fires died down, probably for hundreds of thousands of years.

The study is based on analyses of drill cores from sedimentary layers in four countries: the United Kingdom, Germany, Denmark and Luxembourg. Specifically, the presence of fossil charcoal and molecules formed in smoke from fires was studied. This was combined with data from pollen and spores, which vary in color depending on heat and pressure. They then discovered a “dark zone” that coincides exactly in time with the mass extinction, increasing occurrence of charcoal and the spread of ferns. In other words, the dark zone arose as a result of long-term and intense forest fires.

According to the researchers, lessons can be learned from the inferno 201 million years ago. Higher temperatures and droughts lead to more forest fires and vegetation changes – something we can see on a smaller scale on Earth today.

Facts

Mass extinctions

Five mass extinctions, in which over 50 percent of all animal and plant species became extinct, have occurred on Earth in the last 500 million years. The worst of them occurred at the end of the Permian period, when up to 90 percent of the Earth's species became extinct. The extinction at the end of the Triassic 201 million years ago led to the extinction of a long series of reptile groups, but the dinosaurs survived and were then able to dominate life on Earth until the end of the Cretaceous period 66 million years ago, when they themselves perished in a mass extinction.
 

Brann i tusentals år

Resultatet blev väldiga skogsbränder. Enligt Sylvain Richoz rasade bränderna i Europa i cirka 30 000 år.

– Sannolikt brann stora delar av hela jorden, men vi vet inte med säkerhet, säger han.

När skogarna utplånades ersattes de av ormbunkar som kom att dominera växtligheten under mycket lång tid – en märklig typ av savanner som saknar motsvarighet i dagens värld. Dessa var också eldfängda vilket innebar att bränderna återkom med täta mellanrum.

– Några träd överlevde, men bara i små fickor i landskapet, säger Richoz.

En värld av ormbunkar

Ormbunkarna fortsatte att dominera även efter att bränderna bedarrat, troligen i hundratusentals år.

Studien bygger på analyser av borrkärnor från sedimentära lager i fyra länder: Storbritannien, Tyskland, Danmark och Luxemburg. Specifikt studerades förekomsten av fossilt träkol och molekyler som bildas i rök från bränder. Detta kombinerades med data från pollen och sporer som varierar i färg beroende på värme och tryck. De upptäckte då en ”mörk zon” som sammanfaller exakt i tiden med massutdöendet, ökande förekomst av träkol och ormbunkarnas utbredning. Den mörka zonen uppstod med andra ord som ett resultat av långvariga och intensiva skogsbränder.

Enligt forskarna går det att dra lärdomar av infernot för 201 miljoner år sedan. Högre temperaturer och torka leder till fler skogsbränder och vegetationsförändringar – något vi kan se i mindre skala på jorden i dag.

Fakta

Massutdöenden

Fem massutdöenden, där över 50 procent av alla djur- och växtarter dog ut, har inträffat på jorden de senaste 500 miljoner åren. Det värsta av dem inträffade i slutet av permperioden då uppemot 90 procent av jordens arter dog ut. Utdöendet i slutet av trias för 201 miljoner år sedan ledde till att en lång rad reptilgrupper utplånades, men dinosaurierna överlevde och kunde sedan dominera livet på jorden fram till slutet av kritperioden för 66 miljoner år sedan då de själva gick under i ett massutdöende.