From Planet Earth Online

No one has ever recorded a plant or animal growing again after being frozen for so long. Until now, the physical limit was thought to be just 20 or 30 years for complex life.

If the moss could rejuvenate after even longer, up to tens of thousands of years, it might provide a polar refuge from which life could recover after an ice age.

Scientists from NERC's British Antarctic Survey (BAS) have led research on moss banks at Signy Island north-east of the West Antarctic Peninsula for a number of years.

Using heavy drilling equipment, they dig out thin cores of moss buried in the permafrost over thousands of years, and examine their chemistry and biology for clues as to how the climate has changed over time.

But on this occasion, together with scientists from the University of Reading, they decided to take out another core to see whether moss could grow again after being frozen for so long underground.

We brought it back to the lab in Reading to thaw, and kept them in a plant incubator, at around 17-18 degrees, which is similar to the temperature the growing surface can experience in their natural habitat in the summer,' says Professor Pete Convey of BAS, who led the collaboration.

We checked it every day to see whether there'd been any new growth, then one day we came in and there was this green stuff sitting there.'

Incredibly, the moss at the bottom of the core, which was dated at over 1500 years old, grew back at almost exactly the same time as the newer material at the top.'

Studies on Tardigrades - tiny, but hardy organisms less than 1.5mm in length – have shown that some complex life forms are able to completely shut down their respiratory systems for a period of 10 years or more, and recover when conditions become more favourable.

But throughout that time, their cells become increasingly damaged, and it was thought that this would limit the survival of complex organisms to no more than a few decades.

Nobody can explain yet how the mosses are able to rejuvenate after so long.

The discovery, published in the journal Current Biology, could give scientists a better understanding of how the polar regions will respond to climate change.

There are growing concerns about the release of greenhouse gases such as carbon dioxide and methane from melting permafrost in the Arctic tundra.

But mosses are an effective absorber of carbon dioxide, and if they can bounce back strongly as the permafrost melts, it may help to offset some of those extra greenhouse gas emissions.

The team will now turn their attention to another Antarctic moss bank, which may contain plants up to 6,000 years old.