The oldest signs of life on Earth have just been found in Australia
Rock formations from northwestern Australia represent the remains of microorganisms that lived on Earth nearly 3.5 billion years ago. That’s what the latest research on the first biological life on Earth suggests.
How long has Earth been a biological planet? This is one of the major questions of interest to scientists studying Earth’s oldest rock formations. Our globe formed about 4.54 billion years ago.
How much did it take for oceans to appear and an atmosphere to protect the surface from the effects of cosmic radiation? And later — for the elements to combine into molecules, and for these to become parts of the simplest microorganisms?
The answers to these questions are hidden in stromatolites. These are specific rock formations that are traces of the existence of microorganisms from millions or even billions of years ago. These fossil reefs consist of layers containing distinctive domes, columns and cones. Some of them — such as those found on the cliffs of Spitzbergen — are clearly visible.
How were stromatolites formed?
Life as we know it — that is, having the form of multicellular plants and animals — appeared several hundred million years ago. Before that, however, there were only microorganisms, such as ancient bacteria. Although they were single-celled organisms, they formed vast carpets or sheepskins expertly called mats. They still form today on the surface of the ocean when algae blooms.
Billions of years ago, mats of microbes covered the sea floors. Over time, they were covered by fine sediments. Microorganisms, wanting to regain access to light, moved upward. This is how the cones and domes characteristic of stromatolites were formed, resembling the protuberances in a cardboard egg carton.
Where are the oldest fossils found?
How old are the oldest stromatolites? Which of the oldest rock formations are of biological origin, and which are the result of volcanism and other transformations that Earth’s rocks undergo? The answer to this is not always simple.
In 2016, scientists announced that they had discovered stromatolites 3.7 billion years old in Greenland. That discovery was later disputed. Another group of researchers presented evidence indicating that rocks from Greenland are and always have been simply rocks.
The record holders thus remain the stromatolites found in the so-called Dresser Formation in the Pilbara region of Western Australia. In May 2017, scientists from Australia and New Zealand determined that they are 3.48 billion years old. They published a paper on the subject in the scientific journal Nature Communications at the time.
Confirmed discovery of oldest traces of life
Unlike in the case of Greenland, this second discovery has just been confirmed. The journal Geology published a paper describing a rigorous series of studies that stromatolites from the Dresser Formation underwent. The scientists, led by paleontologist Keyron Hickman-Lewis of the British Natural History Museum, used Raman spectroscopy, inductively coupled plasma mass spectroscopy and scanning electron microscopy, among other methods. And several other methods as well.
With this, according to the researchers, it was possible to confirm that the stromatolites from Australia are of biological origin.
“If archaeologists find the foundations of ruins, they know they were built by humans. They are able to distinguish such characteristic elements as doorways, roads and bricks”, says Hickman-Lewis. — “By the same token, there are certain typical structural elements associated with stromatolites that allow them to identify their formation process and origin”, the researcher adds.
Will we find stromatolites on Mars?
The study — while it relates to the distant past — is also relevant to the future. The Dresser Formation on Mars was just a shallow lagoon with a bacterial mat on the bottom billions of years ago. The same can be said of the large Jezero crater also located on Mars. It is possible that life existed there then as well.
This means that studies like the one described in Geology also have a chance to help identify traces of ancient Martian microorganisms. Provided, of course, that the right rock formations are found first. Research in the Jezero crater is currently being conducted by the Perseverance Mars rover.
Source: Geology, Natural History Museum
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