Tiny bubbles of ancient water trapped in quartz grains in Australia may hold the key to understanding what caused the Earth's first ice age, scientists say.

Researchers at the University of Manchester in England, along with French colleagues, analyzed the amount of ancient atmospheric argon gas isotopes dissolved in the bubbles and found levels were very different to those in the air we breathe today, a finding that could help explain why Earth didn't suffer its first ice age until 2.5 billion years ago despite the Sun's rays being weaker during the early years of our planet's formation.

"Evidence from the geological record indicates that the first major glaciations on Earth occurred about 2.5 billion years ago, and yet the energy of the sun was 20 percent weaker prior to, and during, this period, so all water on Earth should already have been frozen," Manchester researcher Ray Burgess said.

"This is something that has baffled scientists for years but our findings provide a possible explanation," he said in a University release Wednesday.

"High levels of the greenhouse gas carbon dioxide in the early atmosphere -- in the order of several percent -- which would have helped retain the sun's heat, has been suggested as the reason why the Earth did not freeze over sooner, but just how this level was reduced has been unexplained, until now."

The analysis of argon isotopes ratio helped in estimating how the continents have grown over geological time, the researchers said, which would directly affect the amount of carbon dioxide present in the atmosphere.

"The continents are a key player in the Earth's carbon cycle because carbon dioxide in the atmosphere dissolves in water to form acid rain," Burgess said. "The carbon dioxide removed from the atmosphere by this ... acid weathering of this early crust would efficiently reduce the carbon dioxide levels in the atmosphere to lower global temperatures and lead to the first major ice age."