WASHINGTON, April 2 (Xinhua) -- A large fraction of Mars' atmosphere has been lost into space, contributing to the transition in the climate of the Red Planet from an early warm and wet environment to today's cold and dry atmosphere, a new study showed.

The study, published in the journal Science on Friday, showed that about 66 percent of Mars' atmosphere has been lost into space since it formed.

Mars' atmosphere is composed mainly of carbon dioxide, according to the study. Evidence on the planet's surface indicates that Mars was once warmer and wetter, suggesting a thicker atmosphere in the past, it added.

"If it was warm and had liquid water, it could have had the conditions necessary for life to arise," said study coauthor Marek Slipski from the University of Colorado in Boulder.

"One way to learn about what this early atmosphere could have been like is to understand how it's been stripped away, and how much has been removed," Slipski said.

Slipski and his colleagues used two isotopes of the inert gas argon, argon-36 and its heavier sibling argon-38, to measure the escape route of the carbon dioxide.

The lighter argon isotopes tend to spread to the higher layer of Mar's atmosphere and are more easily ejected to space than heavier ones.

Helped by the Mars Atmosphere and Volatile Evolution (MAVEN) space probe, scientists used measurements of the upper-atmospheric structure to determine the amount of gas lost to space through time.

Due to argon's inert nature, scientists pointed to solar wind as one of the main drivers behind Mar's atmospheric loss.

After comparing the ratios of the two isotopes in different layers of the atmosphere, the researchers found that about 66 percent of the planet's argon-36 was lost to space through sputtering.

Sputtering is a process whereby high-speed ions carried by the solar wind slam into Mars and knock atoms out of the atmosphere.

It's not clear how much the loss of argon correlate with overall atmospheric loss, Slipski said. But it does show that sputtering may be responsible for the disappearance of much of the Red Planet's air, he added.