BLACKSBURG, Va., July 23 (UPI) -- All it took was a small bump in oxygen levels on young Earth to encourage animals to take their first breaths. The discovery undermines the theory that a large oxygen jump was the primary driver in the evolutionary transition from algae and sponges to whales, sharks and squids.
To gauge ancient oxygen levels, a team of researchers -- led by scientists from Virginia Tech -- measured iron levels and locations in shale deposits, once mud on the floor of young Earth's oceans. Rock samples from all over the world offered scientists clues as to the chemistry of Earth's ancient oceans.
"We suggest that about 635 million to 542 million years ago, the Earth passed some low, but critical, threshold in oxygenation for animals," Benjamin Gill, an assistant professor of geoscience in Virginia Tech's College of Science, said in a press release. "That threshold was in the range of a 10 to 40 percent increase, and was the second time in Earth's history that oxygen levels significantly rose."
It was that ancient uptick, researchers argue in their new study, that jumpstarted the evolution of oxygen-breathing organisms -- a much smaller threshold than previously estimated.
But Erik Sperling, an assistant professor of geological and environmental sciences at Stanford University, says other factors likely also facilitated the jump from simple microorganisms to complex lineages. Sperling is first author on the new paper published in the journal Nature.
"Going forward we will need much more precise constraints on the magnitude of oxygenation and the physiological requirements of early animals to continue testing the impact of oxygenation on Cambrian animal life," he said.