Life forms appeared at least 60 million years earlier than previously thought

[n2doc]

Geologists from Trinity College Dublin have rewritten the evolutionary history books by finding that oxygen-producing life forms were present on Earth some 3 billion years ago -- a full 60 million years earlier than previously thought. These life forms were responsible for adding oxygen (O2) to our atmosphere, which laid the foundations for more complex life to evolve and proliferate.

Working with Professors Joydip Mukhopadhyay and Gautam Ghosh and other colleagues from the Presidency University in Kolkata, India, the geologists found evidence for chemical weathering of rocks leading to soil formation that occurred in the presence of O2. Using the naturally occurring uranium-lead isotope decay system, which is used for age determinations on geological time-scales, the authors deduced that these events took place at least 3.02 billion years ago. The ancient soil (or paleosol) came from the Singhbhum Craton of Odisha, and was named the 'Keonjhar Paleosol' after the nearest local town.

The pattern of chemical weathering preserved in the paleosol is compatible with elevated atmospheric O2 levels at that time. Such substantial levels of oxygen could only have been produced by organisms converting light energy and carbon dioxide to O2 and water. This process, known as photosynthesis, is used by millions of different plant and bacteria species today. It was the proliferation of such oxygen-producing species throughout Earth's evolutionary trajectory that changed the composition of our atmosphere -- adding much more O2 -- which was as important for the development of ancient multi-cellular life as it is for us today.

Quentin Crowley, Ussher Assistant Professor in Isotope Analysis and the Environment in the School of Natural Sciences at Trinity, is senior author of the journal article that describes this research which has just been published online in the world's top-ranked Geology journal, Geology. He said: "This is a very exciting finding, which helps to fill a gap in our knowledge about the evolution of the early Earth. This paleosol from India is telling us that there was a short-lived pulse of atmospheric oxygenation and this occurred considerably earlier than previously envisaged."

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http://www.sciencedaily.com/releases/2014/09/140904121245.htm

[muriel_volestrangler]

1. Or: oxygen-producing lifeforms appeared 2% earlier than previous thought (nt)

[eppur_se_muova]

2. Yeah, and what's the % margin of error in U-Pb dating ?

Technically, though, the headline is probably correct -- I suspect they used stratigraphy to determine the 60MY interval relative to other oxygenation events, though the article makes it sound otherwise. In general, isotope dating is used to get estimates of the time period involved, but stratigraphy is essential for establishing precise *relative* dates within a sequence. Geologists--including the editor and referees at Geology--know better than to trust small differences between large numbers of limited precision.

[GeorgeGist]

3. My initial thought too but little more.

Thanks for adding to my knowledge.