3.5 billion-year-old fossils challenge ideas about early life on Earth

By | March 27, 2018

Rebecca Boyle writes:

In the arid, sun-soaked northwest corner of Australia, along the Tropic of Capricorn, the oldest face of Earth is exposed to the sky. Drive through the northern outback for a while, south of Port Hedlund on the coast, and you will come upon hills softened by time. They are part of a region called the Pilbara Craton, which formed about 3.5 billion years ago, when Earth was in its youth.

Look closer. From a seam in one of these hills, a jumble of ancient, orange-Creamsicle rock spills forth: a deposit called the Apex Chert. Within this rock, viewable only through a microscope, there are tiny tubes. Some look like petroglyphs depicting a tornado; others resemble flattened worms. They are among the most controversial rock samples ever collected on this planet, and they might represent some of the oldest forms of life ever found.

In December, researchers lobbed another salvo in the decades-long debate about the nature of these forms. They are indeed fossil life, and they date to 3.465 billion years ago, according to John Valley, a geochemist at the University of Wisconsin. If Valley and his team are right, the fossils imply that life diversified remarkably early in the planet’s tumultuous youth.

The fossils add to a wave of discoveries that point to a new story of ancient Earth. In the past year, separate teams of researchers have dug up, pulverized and laser-blasted pieces of rock that may contain life dating to 3.7, 3.95 and maybe even 4.28 billion years ago. All of these microfossils — or the chemical evidence associated with them — are hotly debated. But they all cast doubt on the traditional tale. [Continue reading…]

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