Today’s Image of the Day from NASA Earth Observatory features the rocks of the Pilbara Craton in Western Australia. These are some of the oldest rocks on Earth, dating back between 3.6 and 2.8 billion years.

“The iron-rich rocks here began forming before there was oxygen in Earth’s atmosphere or even life itself. The area also harbors evidence of some of the earliest life – 3.45-billion-year-old fossil colonies of microbial cyanobacteria, the oldest known stromatolites on Earth,” reports NASA.

The stable, geologically inactive core of an ancient continent is known as a craton. The Pilbara Craton has remained intact, surviving the affronts of plate tectonics and erosion since the Archean Eon four billion years ago.

“During the Archean, and the Proterozoic Eon that followed, multiple cratons assembled to form the Australian continent, leaving multiple basins and belts of buckled and folded rocks at their margins. The main cratons that formed Western Australia are the Pilbara and Yilgarn. They began to assemble about 2.2 billion years ago during a mountain-building episode called the Capricorn Orogeny,” explains NASA.

“The land that is today known as the Hamersley Basin was then at the bottom of an ocean lying between the two cratons. The rocks of the basin preserve a record of the last ocean environment in the area before the cratons converged and closed the basin.”

Image Credit: NASA Earth Observatory 

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By Chrissy Sexton, Earth.com Staff Writer