Simple Life Form May Have Existed 700 Million Years Earlier Than Previously Thought

Diamonds 4.2 billion years old found trapped inside the Jack Hills zircon crystals are the oldest-known samples of Earth's carbon. (Credit: Image courtesy of Curtin University)
ScienceDaily (July 8, 2008) — The accepted timeframe for the beginnings of life on Earth is now being questioned by a Curtin University of Technology led team of scientists, after finding a key indicator to the earliest life forms in diamonds from Jack Hills in Western Australia.

The 4.2-billion-year-old diamonds found trapped inside the Jack Hills zircon crystals are the oldest-known samples of Earth’s carbon. The Curtin led team’s discovery of very high concentrations of carbon 12, or “light carbon” within these crystals is remarkable as it is a feature usually associated with organic life.

Dr Alexander Nemchin from Curtin’s Department of Applied Geology and the project leader believes the latest research will revive debate on the early evolution of life on Earth.

“We believe this find to be the oldest terrestrial light carbon reservoir discovered so far,” Dr Nemchin said.

Evidence for ancient life stretches back in time to at least 3.5 billion years ago, in the form of single-celled organisms that did not require oxygen. The discovery of light carbon in the Jack Hills crystals raises the question – did a simple life form exist on Earth 700 million years earlier than previously thought?

“We interpret the range of light carbon values observed in these inclusions as a unique chemical marker that opens up the possibility of biological activity during the period not long after the Earth’s formation,” Dr Nemchin said.

The researchers report the composition of 22 diamond and graphite inclusions from 18 Jack Hills zircon grains in the journal Nature.

“The discovery challenges our fundamental understanding of processes active in the early history of the Earth. It suggests that life may well have appeared on Earth long before the period of heavy-meteorite bombardment believed by some to have initiated the emergence of life on Earth,” Dr Nemchin said.

“Alternatively, it requires some other process to create the light carbon values, which would then question the widely held assumption that light carbon means life.”

The discovery will assist mankind in our understanding of the development of the planet and help us to better assess the conditions of the Earth up to 4.5 billion years ago.

Background

In 1983, a Curtin project team discovered extremely old zircon crystals in a collection of rocks located between Meekathara and Carnarvon. Twenty years later, the oldest diamonds were unexpectedly discovered in these rocks by many of the original team.

The recent paper in Nature is written by a team of people made up of Curtin University academic and Project Leader, Dr Alexander Nemchin, Martin Whitehouse from the Swedish Museum of Natural History, Martina Menneken and Dr Thorston Geisler a Masters student and her supervisor from the University of Munster’s Institute of Mineralogy, and Professors Pidgeon and Wilde from Curtin University’s Applied Geology Department, who originally identified the old zircons