U.K. researchers have found a fossil forest—thickly packed with peculiar trees—from an era that gave Earth some of the first big trees, which in turn may have changed the climate drastically.

“These fossil forests shows us what the vegetation and landscape were like on the equator 380 million years ago, as the first trees were beginning to appear,” said researcher Chris Berry of Cardiff University in the U.K.

The fossils, with stumps preserved in place, turned up in Svalbard, a Norwegian archipelago in the Arctic Ocean.

By coincidence, Svalbard is also where people maintain the Svalbard Seed Vault, a repository of seeds from around the world to be used in case of ecological disaster.

“It’s amazing that we’ve uncovered one of the very first forests in the very place that is now being used to preserve the Earth’s plant diversity,” said Berry.

But Svalbard itself seems to have drifted, as it used to be near the Equator at the time the trees lived, said Berry, who identified the fossil forest and described it Nov. 19 in a report in the journal Geology. Today Svalbard, population 2,500, is one of the world’s northernmost inhabited areas.

The forests grew during a period known as the late Devonian, and could shed light on the cause of a plunge in levels of carbon dioxide in the atmosphere around that time, Berry and colleagues say. This change brought levels of the gas to an estimated one-fifteenth of what they were before.

Current theories suggest that during the Devonian—420 million to 360 million years ago—there was a huge drop in carbon dioxide levels in the atmosphere, thought to be largely caused by a change in vegetation from diminutive plants to the first large forest trees. Forests pulled carbon dioxide out of the air through photosynthesis—the process by which plants create food and tissues—and the formation of soils.

Although initially the appearance of large trees absorbed more of the sun’s radiation, eventually temperatures on Earth also dropped dramatically to levels very similar to those experienced today because of the reduction in atmospheric carbon, the scientists explain.

Because of the high temperatures and large amount of rainfall on the equator, equatorial forests probably contributed most to the drawdown of carbon dioxide, they added.

The team found that the forests in Svalbard were formed mainly of lycopod trees, better known for growing millions of years later in coal swamps that eventually turned into coal deposits, such as those in South Wales. They also found that the forests were extremely dense, with very small gaps, only around 20 cm or 8 inches, between each of the trees, which probably reached about 4m or yards high.

Berry previously worked with American colleagues to describe another slightly older forest, at Gilboa in upstate New York. The Gilboa forest was at least 30 degrees south of the equator at that time, and the tree stumps in place belonged to different types of plants.