From double impact emerges life

Scientists have observed a link between an asteroid and comet impact on Earth and the emergence of primitive bacterial life-forms billions of years ago.

Australian National University scientists believe they may have discovered the beginnings of life in our ancient oceans.
 
By studying the ancient mineral-rich sediments in Western Australia and South Africa, the team discovered the formation of banded iron formations, jasper and iron-rich shale coinciding faithfully with asteroid and comet impacts.
 
According to project leader Dr Andrew Glikson, the collisions of the asteroids and comets with the Earth caused volcanic and hydrothermal activity, including eruptions of iron-rich basalt.
 
It created an environment that encouraged primitive bacteria that lived on the early ocean floor and derived their energy from oxidising water-soluble (ferrous) iron into insoluble (ferric) iron.
 
This bacterial activity is thought to have precipitated iron and silica-rich sediments, known as banded iron formations, in areas such as the Pilbara in Western Australia.
 
These banded iron formations host the huge Hamersley and Yarrie iron ore deposits of the Pilbara region.
 
Dr Glikson made the link when studying extraterrestrial impacts as a factor to the appearance of the banded iron formations.
 
The formations span over hundreds of kilometres in Western Australia, South Africa, Brazil and Canada, and are thought to be 2.4 to 3.5 billion years old.
 
The deposition of iron-rich sediments closely followed massive collisions between asteroids and the Earth at several points in Earth history, including at 3.47, 3.26, 3.24 and 2.63 billion years ago, Dr Glikson discovered.
 
“In the majority of cases, the ejected materials left behind from the impact of the asteroids and comets are directly overlain by iron-rich sediments, suggesting a possible cause and effect link between the large impacts, iron-rich volcanic activity and microbial oxidation of iron,” Dr Glikson said.
 
“The oldest known banded iron formations occur in south-western Greenland, where they are dated as 3.85 billion years old.
 
“The age of these banded iron formations coincides with a period of heavy asteroid bombardment on the moon and on Earth, thus marking the earliest known impacts, volcanism and the emergence of microbial colonies at the sea floor,” he added.
 
The team are currently continuing their study by searching for further evidence of asteroid impact units beneath banded iron formations in the Pilbara region of Western Australia.

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