At http://phys.org/print391942311.html … the world's oldest fossils have been found in Greenland – going back 3700 million years ago (or 3.7 billion years ago) which is surprising as this means bacterial life was present half a billion years after the planet was formed. At this time, and for thousands of millions of years afterwards, life consisted of single cells. Stromatolite fossils are mounds of carbonate constructed by microbial life forms and they represent obvious evidence such communities existed. They are also a fairly complex ecosystem and this may indicate they were influenced by a genetic code.
The stromatolites were uncovered by melting fingers of Greenland glaciers and they seem to show that when they were alive they were living in a shallow marine environment (one of the reasons why the search for water on Mars is so important).
At http://phys.org/print391871395.html … the thrust of the article appears to concern Mars and the idea that life on the red planet cannot yet be excluded. The date of the stromatolites is derived from volcanic ash and tiny crystals of zircon with uranium and lead particles which are of course used in dating methodologies. The piece of rock itself is described as ancient sea floor and here is a mystery. In Plate Tectonics theory ancient sea floor is regularly subducted down into the Mantle – so why is a bit of sea floor dating back almost to the birth of the planet still existing on the surface of Greenland? Was it subducted and then brought back up again – and if so why did it not erase evidence of the stromatolites? If sea floor can survive for 3700 million years on Greenland where does this leave Plate Tectonics? The answer of course is regurgitation – which takes us back full circle. Why weren't the stromatolites gobbled up by the Earth's mantle never to be seen again?