3.5 Billion-Year-Old Fossils Challenge Ideas About Earth’s Start
By: Max Ngamla
Tags: History, Science, Discovery, Life, Earth

3.5 Billion-Year-Old Fossils Challenge Ideas About Earth’s Start

The oldest trace of earthly life confirmed

Artist's impression of early Earth (Wikipedia)

Fossils almost 3.5 billion years old discovered in Australia are the imprint of the oldest known microorganisms that have lived on Earth, scientists have confirmed that life probably appeared much earlier.

For these researchers, the work published in an edition of the Proceedings of the American Academy of Sciences (PNAS), also suggests that life could be frequent in the Universe, at least in the form of micro-organisms.

Fossilized Bacteria Discovered

Researchers from the Universities of California and Wisconsin identified, thanks to new mass spectrometry, chemical signatures of eleven microbial specimens that belong to five species including some similar to those existing today.

“It is the first and oldest place on the planet where we have both the morphological and chemical imprint of life, ” explains John Valley, professor of geochemistry and petrology at the University of Wisconsin, the principal co-author of this study.

“We also discovered that there were several types of metabolisms and different species with different biological functions: some produced methane, others consumed it or used solar energy for photosynthesis,” he told AFP.

The methane was to form an important part of the atmosphere of the very young Earth frequently bombed by comets, where oxygen was scarce or absent.

Some of these bacteria, now extinct, belonged to archaea, a group of prokaryotes, unicellular microorganisms — single-celled living things without a nucleus.

Others were similar to microbial species still found today.

This study thus suggests that some of the micro-organisms, first described in 1993 in the journal of Science, according to their cylindrical morphology and filamentous, could have lived at a time when there was no oxygen on Earth yet.

“These organisms — 0.01 millimeters in width — formed a community of very well developed microorganisms which probably did not constitute the dawn of life, ” sums up Professor Valley.

The fact that different types of microbes were already present 3.5 billion years ago “tells us that life had to start much earlier on Earth, and also confirms that it is not very difficult for a primitive life form to evolve into advanced micro-more organisms ”, points out William Schopf, professor of paleobiology at the University of California, another principal co-author of these works.

For him, this study, along with others, indicates that life could be frequent in the cosmos.

Studies published in 2001 by Professor Valley’s team suggested that the existence of oceans of liquid water could go back 4.3 billion years, over 800 million years before the fossils described in these last works and just 250 million years after the formation of the Earth.

“We have no direct evidence that life existed 4.3 billion years ago but it would have very well could be … and it’s something we all want to know,” notes Professor Valley.

Studies published in the British Journal of Nature reported the discovery of potential signs of life dating back 3.95 billion years, the oldest to this day but which remain to be confirmed.

These fossils were found in grains of graphite, a form of carbon. They were trapped in ancient sedimentary rocks in Canada.