Fossilized pollen is sometimes used to determine what sort of vegetation grew as Earth’s climate changed over time. But until recently, samples could only be dated back about 500,000 years, a relatively narrow window for study. But now researchers in Australia have found a way to date and examine pollen found in stalagmites of any age.

A new technique developed at the University of Melbourne allows researchers to date speleothems (stalagmites, stalactites and flowstones) and then dissolve them to examine the pollen inside.

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“It is also home to a scientific treasure trove of palaeoclimate information that has potential global significance,” said Professor Jon Woodhead, from the University’s School of Earth Sciences.”

Samples from speleothems found in Australia’s arid Nullarbor Plain give clues to what grew in the area 5 million years ago when the area received four times as much rain.

“Most didn’t contain any pollen, which isn’t surprising since many speleothems grew in caves that had no openings to the surface,” palaeoclimate scientist Kale Sniderman said in a statement.

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“But some did contain fossil pollen, which revealed the nature of the vegetation growing at those times. Through that we’ve been able to develop a new understanding of the history of the Nullarbor’s climate.”

The findings were published in the journal Proceedings of National Academy of Sciences.