Study: Life on Earth was kickstarted by this

By Mark Waghorn via SWNS

Life on Earth was kick-started by fluctuating levels of oxygen, according to new research.

Amounts of the energy-producing gas varied wildly a billion years ago - accelerating evolution.

This is when single-celled organisms were beginning to turn into the very first complex creatures.

Lead author Dr. Alex Krause, of the University of Leeds, said the findings shed fresh light on the history of our planet.

Its atmosphere has developed in three stages - the first about two billion years ago and the last roughly 400 million years ago.

What is uncertain is what happened during the second - known as the Neoproterozoic Era.

Explained Dr. Krause: "The early Earth, for the first two billion years of its existence, was anoxic, devoid of atmospheric oxygen. Then oxygen levels started to rise, which is known as the Great Oxidation Event.

"Up until now, scientists had thought that after the Great Oxidation Event, oxygen levels were either low and then shot up just before we see the first animals evolve, or that oxygen levels were high for many millions of years before the animals came along.

“But our study shows oxygen levels were far more dynamic. There was an oscillation between high and low levels of oxygen for a long time before early forms of animal life emerged.

"We are seeing periods where the ocean environment, where early animals lived, would have had abundant oxygen - and then periods where it does not."

The Neoproterozoic started around one billion years ago and lasted for 500 million years - during which time early animal forms emerged.  

Something extraordinary happened that played a pivotal role in this development, say the international team.

The findings in the journal Science Advances are based on fossilized traces of early animals called Ediacaran biota.

They are multi-celled organisms that required oxygen and have been found in sedimentary rocks that are 541 to 635 million years old. 

Dr. Krause and colleagues measured different forms of carbon found in limestone rocks taken from shallow seas.

Chemical ratios enabled them to calculate rates of photosynthesis that existed - and infer quantities of oxygen. 

Results produced a record over the last 1.5 billion years - revealing how much was diffusing into the ocean to support early marine life.

Project supervisor Dr. Benjamin Mills, also from Leeds, said: "This periodic change in environmental conditions would have produced evolutionary pressures where some life forms may have become extinct and new ones could emerge."

The oxygenated periods expanded what is known as "habitable spaces" - parts of the sea where oxygen levels would have been high enough to support animal forms. 

Added Dr. Mills: "It has been proposed in ecological theory that when you have a habitable space that is expanding and contracting, this can support rapid changes to the diversity of biological life.

"When oxygen levels decline, there is severe environmental pressure on some organisms which could drive extinctions.

"And when the oxygen-rich waters expand, the new space allows the survivors to rise to ecological dominance.

"These expanded habitable spaces would have lasted for millions of years, giving plenty of time for ecosystems to develop."

The study shows it took half a billion years for oxygen to hit the level that allowed the explosion of animal life.

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

The increase occurred in fits and starts spread over a vast period rather than a change in animal behavior.

It is vital for understanding both the climate system and why life is on Earth in the first place.