With every new discovery of fossils, it seems, the first appearance of life on Earth is earlier.
Maybe.
There is always controversy, and your belief about the earliest date may depend on just how hellish you think the Hadean period was, when asteroids bombarded the planet and life probably would have been impossible.
Nicholas Wade writes at the New York Times, “Geologists have discovered in Greenland evidence for ancient life in rocks that are 3.7 billion years old. The find, if confirmed, would make these fossils the oldest on Earth and may change scientific understanding of the origins of life.
“Experts are likely to debate whether the structures described in the new report were formed biologically or through natural processes. If biological, the great age of the fossils complicates the task of reconstructing the evolution of life from the chemicals naturally present on the early Earth. It leaves comparatively little time for evolution to have occurred and puts the process close to a time when Earth was being bombarded by destructive asteroids. …
“Certain features ‘are fairly credible hallmarks of microbial activity,’ Abigail C. Allwood of Caltech’s Jet Propulsion Laboratory wrote in a commentary accompanying the Nature article [by Allen P. Nutman et al.]. They have a few features that make them ‘interesting and possibly biological,’ she added in an email.
“Another expert in the early Earth’s environment, Tanja Bosak of M.I.T., said the structures do resemble modern stromatolites but their origin ‘will be hotly debated.’ …
“Dr. Nutman argues that life must therefore have originated even earlier, probably in the late Hadean stage of Earth’s history, which lasted from 4.65 billion years ago — when the planet formed from debris in orbit around the sun — to 4 billion years ago.
“But the Hadean was so called because of the hellish conditions thought to have prevailed, including cataclysmic meteorite impacts that boiled the oceans into steam and turned Earth’s surface into molten lava. The largest of these impacts, at 4.5 billion years ago, tore a piece from Earth that became the moon. It is difficult to see how life could have begun under such circumstances.”
Weigh in on the controversy here.
Photo: Allen Nutman
Stromatolites from Greenland may be evidence of the oldest life on earth.
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