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18-Jun-2009

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Plant fossils shed light on extinction



Lepidopteris, a plant which became extinct at the Triassic-Jurassic boundary.

Plant fossils from Greenland tell us that the number of plants there decreased abruptly about 200 million years ago, when the Triassic period ended and the Jurassic period began, researchers say in the latest issue of Science. They also say that this sharp drop in plant life happened when atmospheric carbon dioxide levels and global warming were on the rise.

That period of time, known as the Triassic-Jurassic boundary, is known for one of the largest extinction events in Earth's history when many marine species disappeared from the planet and the dinosaurs started to appear.

This new finding about ancient plant life might help researchers to understand some of the causes of massive extinctions like that one. It could also help them understand the pace at which these extinctions take place.



200-million-year-old cycads and conifers from East Greenland.

Jennifer McElwain and colleagues examined the history of six fossil plant groupings from the Triassic-Jurassic boundary at a site in East Greenland in order to reach their conclusions. They found that the total number of plant groupings, as well as the number of individual plants, decreased as the massive extinction event took place.

These researchers suggest that this abrupt loss of plant diversity reflects the plants' responses to very rapid environmental changes perhaps caused by a meteorite impact or an eruption of gas from the Earth but not the slow environmental changes that researchers had previously predicted for that time period.

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This article appears in the 19 June 2009 issue of Science.