New clues to the origin of life on Earth from microbial remains in ancient rocks

UNSW scientists have discovered that Western Australia's famous stromatolites dating back more than 3.5 billion years contain some of the remotest microbial remains of life on Earth.

Scientists have discovered exceptionally preserved microbial remains in some of the oldest rocks on Earth in Western Australia – a major breakthrough in the field, which offers clues to the origin of life on Earth.

UNSW researchers have discovered the organic matter contained in stromatolites – fossilized microbial structures – from the former Dresser Formation in the Pilbara region of Western Australia.

Stromatolites are of biogenic origin since their discovery in the 1980s. However, despite strong textural evidence, this theory has not been proven for nearly 40 years because scientists have not been able to demonstrate the presence definite remains of preserved organic matter – until today's publication of the prestigious journal. Geology.

"It's an exciting discovery. For the first time, we are able to show the world that these stromatolites are irrefutable evidence of the very first life on Earth, "says Dr. Raphael Baumgartner, Principal Investigator at the Australian Center for Astrobiology. in the team of Professor Martin Van Kranendonk at UNSW.

According to Professor Van Kranendonk, this discovery is the closest the team has done to a "smoking gun" to prove the existence of such an ancient life.

"This represents a major advance in our knowledge of these rocks, in the science of early childhood investigations in general and, more specifically, in the search for life on Mars. We now have a new target and a new methodology to look for old traces of life, "says Professor Van Kranendonk.

Deep drilling, looking closely

Since the formation of Dresser was discovered in the 1980s, scientists wondered if these structures were truly microbial and therefore the first signs of life.

"Unfortunately, there is a climate of mistrust of textural biosignatures in the world of research. Therefore, the origin of stromatolites in Dresser's training has been a hotly debated topic, "says Dr. Baumgartner.

"In this study, I spent a lot of time in the lab, using micro-analysis techniques to take a close look at the rock samples, to prove our theory once and for all."

The stromatolites of the Dresser formation usually come from the surface of the rock and are therefore very altered. For this study, scientists worked with samples taken deeper into the rock, under the weathering profile, where stromatolites are exceptionally well preserved.

"Examining drill core samples allowed us to visualize a perfect snapshot of ancient microbial life," says Dr. Baumgartner.

Using a variety of cutting-edge tools and advanced micro-analytical techniques, including high power electron microscopy, spectroscopy and isotopic analysis, Dr. Baumgartner analyzed the rocks.

He discovered that stromatolites are essentially composed of pyrite – a mineral also called "mad gold" – which contains organic matter.

"The organic matter we found preserved in stromatolite pyrite is exciting. We are looking at exceptionally preserved coherent filaments and filaments that are typically microbial biofilm residues, "says Dr. Baumgartner.

The researchers say that such remains had never been seen before in Dresser's training and that having seen the evidence under the microscope was incredibly exciting.

"I was quite surprised – we never expected to find this level of evidence before starting this project. I remember the night under the electron microscope where I finally realized that I was looking at the remains of biofilm. I think it was around 11 pm, when I had that "eureka" moment, and I stayed until three or four in the morning, just for imaging and imaging because I was so excited. I've totally lost track of time, "says Dr. Baumgartner.

Indices of the search for life on Mars

A little over two years ago, Dr. Baumgartner's colleague Tara Djokic, a doctoral candidate at UNSW, discovered stromatolites in hot-spring deposits in the same region of Western Australia, delaying 580 million the number of microbial lives on Earth.

"Tara's main discoveries have been these exceptional geyserite deposits, which indicate that there have been geysers in this area, and therefore expulsions of fluid on an exposed surface," says Dr. Baumgartner.

"His study focused on the broader geological setting of the paleo-environment – providing support for the theory that life began on the earth rather than in the ocean – while my study really deepened the finer details of the stromatolite structures of the region. . "

Scientists say the two studies help us answer a central question: where does humanity come from?

"Understanding where life could have emerged is really important to understanding our ancestry. And from there, it could help us understand where life could have happened – for example, where it was launched on other planets, "says Dr. Baumgartner.

Last month, scientists from NASA and the European Space Agency (ESA) spent a week in the Pilbara with Martin Van Kranendonk for specialized training in identifying signs of life in these same rocks old. It was the first time Van Kranendonk shared knowledge of the region with a dedicated team of Mars specialists – a group comprising NASA and ESA Mars 2020 mission leaders.

"It is deeply gratifying that the ancient Australian rocks and our scientific know-how are making a significant contribution to our quest for extraterrestrial life and the discovery of the secrets of Mars," said Professor Van Kranendonk.

Reference: "Nanoporous pyrite and organic matter in 3.5 billion year old stromatolites record a vital life" by Raphael J. Baumgartner, Martin J. Van Kranendonk, David Wacey, Marco L. Fiorentini, Martin Saunders, Stefano Caruso, Anais Pages, Martin Homann and Paul Guagliardo, September 25, 2019, Geology.
DOI: 10.1130 / G46365.1