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Research by the University College London conducted into rock tracing procedures have discovered that it took 100 million years for oxygen levels in the earth to rise, allowing animal life to expand about 600 million years ago.

Before this, scientists were not too sure how quickly the earth got oxygenated, and whether the "explosion of animal life" was earlier than this or not.

"We want to find out how the evolution of life links to the evolution of our climate," Philip Pogge von Strandmann, lead researcher of the study, said in a press release."The question on how strongly life has actively modified Earth's climate, and why the Earth has been habitable for so long is extremely important for understanding both the climate system and why life is on Earth in the first place."

Looking at rocks across the U.S., Canada and China that had been laid down under the sea, and piecing them together gave a picture of how the oxygen in the earth rose. Assessing selenium isotopes in the rocks helped them to assess that it took just 100 million years for the oxygen in the atmosphere to expand from less than one percent to over 10 percent of the current levels.

"We took a new approach by using selenium isotope tracers to analyze marine shales which gave us more information about the gradual changes in oxygen levels than is possible using the more conventional techniques used previously," von Strandmann said. "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 behavior."

These findings are only just the first steps towards a deeper understanding of the time taken by the process, and a firmer understanding of alien life.

The findings were published in Dec. 18 issue of Nature Communications.