Daily Archives: July 23, 2013

The colonization of land by life pushed back in time


Fossile lifeA recent story on Science Daily made me stop and read with fascination. It’s about the discovery of fossils that showed life colonized land more than two billion years ago. That’s a shocker, because all indicators are that the Earth was a hostile place, land was barren, and life was a lot simpler.

But apparently we underestimated the ability and tenacity of life. This gives us hope that life may exist on other planets or moons.

Mars, at least its surface, is unlikely to harbour life now, but may have in its water-rich past. We may find fossils. Europa, Jupiter’s ice-covered moon, may have life in the oceans under its surface. Finding out will be tough. Titan? A remote possibility. But these fossils give us new hope: life can survive in very hostile conditions.*

Conventional scientific wisdom has it that plants and other creatures have only lived on land for about 500 million years, and that landscapes of the early Earth were as barren as Mars. A new study, led by geologist Gregory J. Retallack of the University of Oregon, now has presented evidence for life on land that is four times as old — at 2.2 billion years ago and almost half way back to the inception of the planet.hat landscapes of the early Earth were as barren as Mars.

That raises several interesting ideas. First, what sort of life was it? The researchers don’t know for sure, but it’s a bit like slime mold or some lichen. It was tiny, but rather complex given its age and a promising candidate for the oldest known eukaryote. Sci-news notes:

Diskagma buttonii are very small – about 0.3 – 1.8 mm long. They most resemble modern soil organisms called Geosiphon, a fungus with a central cavity filled with symbiotic cyanobacteria.

It was something not quite animal or plant – something simple. But not that simple: they appear to have had symbiotic cyanobacteria in their interiors. Cyanobacteria appeared about 3 billion years ago, and started photosynthesizing (with water as a reducing agent) and making oxygen between then and about 2.6 billion years ago (life itself first showed up about 3.5 billion years ago but some estimates push it much earlier, to 4.3 billion).**

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