World's Largest 'Fossil Forest' Found In US

Scientists have found a 300-million-year-old subterranean 'fossil forest' in the US, thought to be more than 50 times bigger than anything of its kind previously discovered.

Researchers uncovered the forest, which is believed to extend for up to 100 miles, encased in shale above coal seams in the state of Illinois.

Complete trees, delicate ferns and even cockroach wings were fossilised during the carboniferous "coal age" after global warming caused rising water levels, which are believed to have flooded forests and choked them with sediment.

The forest is entombed in eight working coal mines in depths that vary from 250ft to 800ft below ground level and researchers believe the forest may extend for 100 miles.

Palaeontologist Dr Howard Falcon-Lang, from Royal Holloway, who explored the site, told Sky News Online: "This is the largest fossil forest ever discovered, preserved over tens of square kilometres.

"It's from a time when North America and Europe lay on the equator and were covered by steamy tropical rainforests.

"The fossils are spectacular and shed light on an amazing 'lost world' of the Earth's first rainforests."

The compacted remains of these forests are preserved above the coal seams and built on compressed layers of peat. After the coal is extracted the fossils can be seen in the mine ceiling.

"It is an amazing experience to explore these primeval forests in underground coal mines," Dr Falcon-Lang told Sky News.

"The flash photography doesn't really do justice to what it is like. It's completely dark down there and we use the spotlight on our miners' headlamps to illuminate the fossils."

Because of the remarkable preservation of delicate organic matter in the sediment that eventually turned to shale, scientists believe the forest was repeatedly flooded by rising water levels.

Researchers have found a river as wide as the Mississippi snaking its way through the forest. Few animal fossils have been found - except for cockroach wings - as the creatures could flee the slow floods.

"It is extraordinarily rare to get fossil forests of any extent at all," Denver Museum of Nature and Science paleo-botanist Kirk Johnson said.

"It's usually just a few trees here and there. But here is an ancient geography - effectively unheard of."

Researchers have traced a five-mile route through the forest, stopping to measure huge fossilised trees still stand rooted in their original but compacted soil, surrounded by fallen leaves.

Seed ferns prevail close to the river, but further away from the ancient watercourse tree ferns and huge scale trees dominate.

One fallen scale tree, measuring more than 100ft long, was traced by researchers until it disappeared into an as yet unexploited coal seam.

Scientists say birds had not evolved during the era but insects grew immense in the oxygen-rich environment - with dragonflies the size of magpies and 6ft millipedes - although the vegetation was not as vulnerable to insect attack as present day foliage is.

Academics hope to explore as far as possible to provide an ecosystem mapping and analysis on an unprecedented scale to help them with predictions of modern global warming.

Illinois State Geological Survey team member Scott Elrick said: "With our own CO2 rises and changes in climate.

"We can look at the past here and say, 'It has happened before.'"