Evidence of 419mya Wildfire (With Coprolite)

["Richard W. Travsky" <rtravsky@uwyo.edu>]

http://dsc.discovery.com/news/briefs/20040426/wildfire.html

One stormy day in the Silurian Period, about 419 million years ago,
lightning struck a Lilliputian forest and left behind charred plants that
today mark Earth's oldest known wildfire.

The tiny charred plant fossils, found in rocks from the Welsh Borders of
England, give tantalizing clues to life on the land in those early days,
said paleobotanist Ian Glasspool of the Cardiff University School of Earth
Ocean and Planetary Sciences. 

The ancient fire also hints at how much oxygen there was in the
atmosphere  an even harder thing for paleotologists to figure out.

"There was quite a dynamic environment," said Glasspool of the time before
there were many land plants and even fewer land animals. "We've got these
very tiny plants, then we've got this lightning strike."

Some of the tiny forest, fractions of an inch high, burned and other parts
smoldered, he said.

Remarkably, fossil plants are three-dimensional  not squashed like other
fossils  and about 5/32 of an inch tall (4-1/2 millimeters) and 1/64 of an
inch wide (one-half millimeter). Also preserved by the charring was a
single coprolite, or fossilized feces, probably from a plant-eating
millipede-like animal.

The discovery by Glasspool, Dianne Edwards and Lindsey Axe is featured in
the May issue of the journal Geology. 

Although it's not clear exactly how the minuscule "rhyniophytoid" plants
were preserved so well, a low-temperature smoldering fire appears to have
caused at least some of the plants to char and become carbonized. That
made the plants resistant to decay and able to withstand eons of being
buried without being squashed flat, said Glasspool.
...
The other very important aspect of the discovery is what it might say
about oxygen levels in the Silurian atmosphere, said paleobotanist Paul
Strother of Boston University. There had to be at least 13 percent oxygen
in the air for the plants to burn at all, but much more would have caused
a hotter fire and reduced the plants to ashes, leaving no fossils.

Previous researchers have put the Silurian oxygen levels at about 18
percent (compared to today's 21 percent). That would make for cooler fires
that might be more likely to leave behind charred plants like those they
have found, Glasspool said.