London, Dec 19 (IANS): It took 100 million years for oxygen in the oceans and atmosphere to increase to the level that allowed the explosion of animal life on the Earth about 600 million years ago, according to new research.

It is, therefore, likely that early animal evolution was kick-started by increased amounts of oxygen, rather than a change in animal behaviour leading to oxygenation.

"We wanted to find out how the evolution of life links to the evolution of our climate," said lead researcher Philip Pogge von Strandmann from the University College London (UCL).

Researchers tracked what was happening with oxygen levels globally 770-520 million years ago using new tracers in rocks across the US, Canada and China.

By measuring selenium isotopes in the rocks, the team revealed that it took 100 million years for the amount of oxygen in the atmosphere to climb from less than one percent to over 10 percent of today's current level.

This was arguably the most significant oxygenation event in Earth history because it ushered in an age of animal life that continues to this day.

"We were surprised to see how long it took Earth to produce oxygen and our findings dispel theories that it was a quick process caused by a change in animal behaviour," added Strandmann.

Till date, it was not known how quickly the Earth's oceans and atmosphere became oxygenated and if animal life expanded before or after oxygen levels rose.

The study was published in the journal Nature Communications.