Scientists have discovered the oldest known population of plant root stem cells in a 320 million- year-old fossil, providing a window into how ancient roots developed.

The research marks the first time an actively growing fossilized root has been discovered – in effect, an ancient plant frozen in time.

The cells, which gave rise to the roots of an ancient plant, were found in a fossilized root tip at Oxford University in the UK.

“I was examining one of the fossilized soil slides as part of my research into the rooting systems of ancient trees when I noticed a structure that looked like the living root tips we see in plants today,” said Alexander Hetherington, a PhD student at Oxford.

“It gives us a unique window into how roots developed hundreds of millions of years ago,” he said.

Stem cells – self-renewing cells responsible for the formation of multicellular organisms – are located in plants at the tips of shoots and roots in groups called meristems. The 320 million-year-old stem cells are different to all those living today, with a unique pattern of cell division that remained unknown until now.

That tells us that some of the mechanisms controlling root formation in plants and trees have now become extinct and may have been more diverse than thought.

These roots were important because they comprised the rooting structures of the plants growing in the Earth’s first global tropical wetland forests with tall trees over 50m in height and were in part responsible for one of the most dramatic climate change events in history.

The evolution of deep rooting systems increased the rate of chemical weathering of silicate minerals in rocks – a chemical reaction that pulled carbon dioxide out of the atmosphere, leading to the cooling of the Earth and thus one of the planet’s great ice ages.

The fossils studied during this research are the remains of the soil from the first giant tropical rainforests on Earth

. The rock in which the soil is preserved formed in the Carboniferous swamps that gave rise to the coal sources spanning what is now Appalachia to central Europe, including the coal fields in Wales, northern England and Scotland.

The study is published in the journal Current Biology.