March 2 (UPI) -- Scientists have found a new way to mine the fossil record for clues to Earth's ancient climates. As new research reveals, the signatures of ancient atmospheric conditions remain trapped in fossilized plant leaf wax.
As global warming continues, scientists predict Earth's atmosphere will host larger concentrations of water vapor. Like CO2 and methane, water vapor is a greenhouse gas. It's prevalence will further alter Earth's climate, specifically precipitation patterns.
To better understand the influence of water vapor on the planet's climate, scientists are looking to the past.
"If we want to understand how the Earth would work with a climate substantially warmer than today, we have to study intervals millions of years in the past -- made difficult because these warm climates are much older than our oldest climate records from Antarctic ice cores," Yvette Eley, researcher at the University of Birmingham, said in a news release.
The oldest Antarctic ice cores are less than a million years old.
Scientists have tried to locate the signatures of ancient climate conditions in a variety of fossil sources, but the results have been inconsistent. Now, scientists are looking to leaf waxes for help.
"Our new approach to quantifying ancient atmospheric moisture content relies on the fundamental properties of plant leaves, and how they alter their protective waxy coverings in response to water stress," Eley said. "These leaf waxes are tough and resistant, and are regularly found as what we call biomarker compounds in ancient river, lake and even marine sediments."
Scientists developed a method for estimating ancient water vapor concentrations using ratios of compounds found in fossilized plant wax. The method can be used to analyze waxes found in sediments dating to several hundred million years ago.
Researchers tested the accuracy of their new method using modern soils collected in the United States and Central America. The results of their experiments -- published in the journal Scientific Reports -- confirmed a predictable correlation between moisture levels and the ratios of waxy compounds found in sediments.
"What we see is that the distribution of organic compounds preserved in soils seems to be strongly related to the difference between how much water is in an air mass, and how much the air mass can hold, or what is known as the vapour pressure deficit," said Michael Hren, a researcher at the University of Connecticut's Center for Integrative Geosciences.
When researchers used their method to analyze the climate conditions in modern-day Spain between 15 to 17 million years ago, they found evidence confirming the link between temperature and atmospheric moisture content. The data suggests the time period was marked by a cooling trend and a decline in water vapor.
"This gives us the confidence that our proxy works, and we have every reason to believe that it will do so for future exploration into the even deeper past," Eley said. "We hope the results of this exploration will provide direct data to test our understanding of the relationship between global warming, atmospheric moisture content and rainfall systems."