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300 Million-year-old Forest

February 21, 2012 by staff 

300 Million-year-old Forest, Researchers have discovered a 300-million-year-old tropical forest, which was preserved in ash when a volcano erupted in what is today northern China.

University of Pennsylvania paleobotanist Hermann Pfefferkorn and colleagues presented a reconstruction of this fossilised forest, lending insight into the ecology and climate of its time.

Pfefferkorn, a professor in Penn’s Department of Earth and Environmental Science, collaborated on the work with three Chinese colleagues: Jun Wang of the Chinese Academy of Sciences, Yi Zhang of Shenyang Normal University and Zhuo Feng of Yunnan University.

The study site, located near Wuda, China, is unique as it gives a snapshot of a moment in time. Because volcanic ash covered a large expanse of forest over the course of only a few days, the plants were preserved as they fell, in many cases in the exact locations where they grew.

“It’s marvellously preserved. We can stand there and find a branch with the leaves attached, and then we find the next branch and the next branch and the next branch. And then we find the stump from the same tree. That’s really exciting,” said Pfefferkorn.

The researchers also found some smaller trees with leaves, branches, trunk and cones intact, preserved in their entirety.

Due to nearby coal mining activities unearthing large tracts of rock, the size of the researchers’ study plots is also unusual.

They were able to examine a total of 1,000 m2 of the ash layer in three different sites located near one another—an area considered large enough to meaningfully characterize the local paleoecology.

The fact that the coal beds exist is a legacy of the ancient forests, which were peat-depositing tropical forests. The peat beds, pressurised over time, transformed into the coal deposits.

The scientists were able to date the ash layer to approximately 298 million years ago. That falls at the beginning of a geologic period called the Permian, during which Earth’s continental plates were still moving toward each other to form the supercontinent Pangea. North America and Europe were fused together, and China existed as two smaller continents. All overlapped the equator and thus had tropical climates.

At that time, Earth’s climate was comparable to what it is today, making it of interest to researchers like Pfefferkorn who look at ancient climate patterns to help understand contemporary climate variations.

In each of the three study sites, Pfefferkorn and collaborators counted and mapped the fossilised plants they encountered. In all, they identified six groups of trees. Tree ferns formed a lower canopy while much taller trees—Sigillaria and Cordaites—soared up to 80 feet above the ground.

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