Buried beneath a coal mine in Mongolia, scientists have discovered a 'Pompeii-like' forest, 300 million years old, buried by volcanic ash.
Because volcanic ash covered a large expanse of forest over the course of only a few days, plants were preserved as they fell, in many cases in the exact locations where they grew.
"It's marvelously preserved," says University of Pennsylvania paleobotanist Hermann Pfefferkorn.
"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."
The researchers also found some smaller trees with leaves, branches, trunk and cones intact, preserved in their entirety.
Because local coal mining has uncovered large tracts of rock, the researchers were able to examine a total of 1,000 square meters of the ash layer, spread between three different sites nearby.
The team has dated the ash layer to around 298 million years ago, the beginning of the Permian period.
Back then, the Earth's continental plates were still moving toward each other to form the supercontinent Pangea, and the climate was comparable to today's.
In each of the three study sites, Pfefferkorn and collaborators counted and mapped the fossilized plants they encountered. In all, they identified six groups of trees, some up to 80 feet high, with tree ferns forming a lower canopy.
The researchers also found nearly complete specimens of a group of trees called Noeggerathiales - extinct spore-bearing trees, relatives of ferns. While these have previously been found at sites in North America and Europe, they appear to be much more common in these Asian sites.
"This is the first such forest reconstruction in Asia for any time interval, it's the first of a peat forest for this time interval and it's the first with Noeggerathiales as a dominant group," says Pfefferkorn. "It's a time capsule."