Looking in the Wrong Place?

Research out of the University of Copenhagen suggests that we have been looking in the wrong place for a source of oxygen that had to have been present for life to evolve on earth at the end of the Proterozoic eon. The story, in ThaiIndian states:

By analysing the isotopes of chromium in iron-rich sediments formed in the ancient oceans, a scientific team, led by Professor Robert Frei at the University of Copenhagen in Denmark, has found that a rise in atmospheric oxygen levels 580 million years ago was closely followed by the evolution of animal life.

The data offers new insight into how animal life - and ultimately humans - first came to roam the planet.

“Because animals evolved in the sea, most previous research has focussed on oceanic oxygen levels,” explained Newcastle University’s Dr Simon Poulton, one of the authors of the research paper.

“Our research confirms for the first time that a rise in atmospheric oxygen was the driving force for oxygenation of the oceans 580 million years ago, and that this was the catalyst for the evolution of large complex animals,” he added.

Distinctive chromium isotope signals occur when continental rocks are altered and weathered as a result of oxygen levels rising in the atmosphere.

According to the research, oxygen levels began to rise around 2.8 Gya but dropped again and did not experience its second rise until around 580 Mya. This would put it after the the most recent (Kaigas) of the "snowball earth" periods (assuming that is a viable theory).

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Early Life and the "Snowball Earth"

Evidence is building that between 850 and 500 million years, the earth was subjected to a series of mega-ice ages that resulted in a condition called "snowball earth." Now it is being suggested that this "snowball earth" may have been enough to give life its needed boost. An article in the NewScientist, by Douglas Fox and Michael La Page recounts the recent discoveries leading to this:

Some of the biggest finds have come from an ancient seabed in China, called the Doushantuo Formation, where unusual conditions preserved some extraordinary fossils. Layers between 550 and 580 million years old, during the last part of the Ediacaran, contain tiny spheres consisting of anything from one to dozens of different cells - just like the early embryos of animals. Some have suggested they are the remains of giant bacteria, but a series of studies over the past decade have left little doubt that they really are animal embryos.

In 2007, for instance, Leiming Yin of the Nanjing Institute of Geology and Paleontology in China reported finding embryos encased inside hard, spiky shells - unlike anything produced by bacteria. What is more, shells that are identical apart from the lack of preserved embryos on the inside can be found in rocks as old as 632 million years - the dawn of the Ediacaran - suggesting that the animal embryos themselves go back this far.

How did the ice ages play a role?

"This glaciation reset the chemistry of the oceans," he says. Ice caps covering the continents halted delivery of sulphur to the oceans and cut off production of hydrogen sulphide. "You have changes in ocean chemistry like an increased availability of molybdenum and zinc," says Ariel Anbar, a biogeochemist at Arizona State University in Tempe, "all of which play into making the world more hospitable for eukaryotes and ultimately, metazoans."

Sponges or something like them would have been the first animals on the scene. They lack a nervous system and have no need for circulatory systems. Animals like jellyfish might also have evolved early.

More pieces of the puzzle.

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