Stromatolite fossil dating
The fossils, which have been cut away from the rocky outcrop and are now under analysis in Australia, contain tiny cones, just 1 to 4 centimetres tall, and the researchers say their structures and internal layering look exactly like other ancient and modern stromatolites."The texture of the surrounding rocks suggests that they were laid down at the bottom of a shallow sea, much as stromatolites are today in places such as the Bahamas and W"And the rocks contain carbonate minerals such as dolomite, which are also common in younger stromatolites."If the team can confirm that these really are the ancient marks of 3.7-billion-year-organisms, it’s going to make life difficult for those tasked with explaining how evolution could have produced such relatively complex organisms so early on in Earth’s lifespan.
To have had time to evolve into organisms associated with stromatolites formations, Nutman and his team suggest that life on Earth would have likely originated during the Hadean stage of our planet’s history, which runs from Earth’s formation around 4.65 billion years ago - when debris in orbit around the Sun accumulated into our planet - to around 4 billion years ago."[E]ven when the Hadean ended, a final rain of large asteroids descended on Earth at the beginning of the ensuing Archaean stage, possibly set loose when the giant planets Saturn, Uranus, and Neptune drifted out into the Kuiper belt of asteroids," says Wade."This cataclysm, known as the Late Heavy Bombardment, hit Earth between 3.9 and 3.8 billion years ago."So how did life evolve through all of this chaos?
By the late Oligocene, Caribbean coral reefs achieved their greatest development, and by the early Miocene, coral reefs globally had extended to beyond 10° north and south.
Calcite is less stable over time than aragonite, but can form in waters of higher CO concentrations were falling and sea water was warming in tropical areas, whereas at high-latitudes it became cooler.
The team will now have to find supporting evidence that their fossils contain signs of ancient life, because while there's a case to be made, not everyone is convinced."I’ve got 14 queries and problems that need addressing before I’ll believe it," Roger Buick, a geobiologist at the University of Washington, who was not involved in the research, told Alexandra Witze at"If we found something like this on Mars would we stick a flag in it and call it life?
I don’t think we would," adds Abigail Allwood, an astrobiologist at NASA’s Jet Propulsion Laboratory in California.
The oldest fossils ever discovered have been found in Greenland, and they appear to have preserved the earliest signs of life of Earth.
Dated to around 3.7 billion years ago, the fossils contain evidence of stromatolites - layers of sediment packed together by ancient, water-based bacterial colonies - and could push back the origins of life in the fossil record by 220 million years.