Earth’s oldest living landscape discovered in South African rock cores

(ORDO NEWS) — Beneath the Barberton Mahonjwa Mountains, home of South Africa’s first gold rush, lies something more scientifically valuable than any precious metal: Earth’s first terrestrial ecosystem, trapped in a 3.2-billion-year-old rock formation called the Moodys Group.

In clearings and mines, scientists have already seen the fossilized remains of slimy microbial mats thought to have covered ancient rivers, beaches and estuaries. Now they are drilling for the first time, extracting fresh samples of what may have been Earth’s first oxygen-producing microorganisms.

“It’s very fortunate that there are such ancient sites,” says Tanya Bosak, a geobiologist at the Massachusetts Institute of Technology who is not involved in the project.

Although older signs of life have been found in South Africa, Australia and possibly Greenland in what were once oceanic deposits, nowhere else has primitive life on land been so conclusively documented, she says. “This spans a not-so-understandable period in Earth’s history.”

When the Moody group formed, the Earth was almost unrecognizable. Its atmosphere, rich in methane and carbon dioxide but almost devoid of oxygen, kept the planet warm while the Sun was young and weak.

There was not enough land because plate tectonics – the process of forming continents – was just beginning. Here and there, however, volcanic archipelagos such as the Mudisa group pierced the waters.

Beaches ringing volcanoes would be an ideal place for life to develop and spread, says Christoph Heubeck, a sedimentary geologist at the Friedrich Schiller University of Jena. He leads the $2 million Barberton Archaean Surface Environments (BASE) project, which plans to complete its eighth and final core next month.

The cores, which the team has already extracted from deposits at a depth of 200 meters, are rich in petrified mucus. “We’ve drilled hundreds of meters,” Heubeck says. However, their nature remains a mystery.

Other ancient microbial fossils in the Moodies group found in marine and subsurface sediments likely fed on sulfates or used a primitive form of photosynthesis to feed on iron. But those metabolic pathways couldn’t work well in the sun-soaked, shallow waters that slime molds lived in.

Heubeck believes that these microbes were the early ancestors of cyanobacteria, which oxygenated the atmosphere about 800 million years later in what is known as the Great Oxidation Event. “Oxygen production appears to be a process invented early in Earth’s history,” he says.

This is a controversial statement. If oxygen-producing photosynthesis had evolved so early, some researchers argue, the Great Oxidation Event would have followed immediately. However, evidence for the existence of early “oxygen oases” is growing.

Geochemists have discovered mineral deposits that formed long before the Great Oxidation Event that needed oxygen to form.

And genetic analysis of cyanobacteria shows they evolved on land around the same time as the Moodies Group, says Patricia Sanchez-Barakaldo, a paleobiologist at the University of Bristol who is not affiliated with BASE. “Genomic records are independent and consistent with the idea that these were the early ancestors of cyanobacteria.”

Heubeck and his colleagues are hoping that fresh, unaltered microbial mats in cores will provide decisive evidence: geochemical traces of oxygen production that were missing from previous, discovered samples.

This search will begin later this year, when the team will begin to examine half of the cores at “sampling” in Germany; the other half will remain in South Africa as an archive.

Cores may contain other scientific treasures as well. In 2010, Emmanuel Javot, an astrobiologist at the University of Liege, reported that spherical microbial fossils up to 300 micrometers in diameter, hundreds of times the size of an ordinary bacterium, were found in clayey rocks mined from a gold mine in the Moody group.

Some believed that these microorganisms are the world’s oldest eukaryotes – organisms with complex cells similar to our own, for 1 billion years, but the confirmation was inconclusive. Javeau hopes that BASE cores will reveal the same fossils in better condition. “Now we just have to find them,” she says.

BASE cores may also contain clues about the climate of that ancient landscape. One core contains what appear to be lithified layers of soil, which may reflect indicators of atmospheric composition. Marine shales may reflect the process of erosion of the volcanic basalt of the islands.

Whether it broke off in pieces, as happens in the modern Arctic, or was ground to pieces, as in tropical climates, this can give an idea of ‚Äč‚Äčancient temperatures.

Other specimens have captured the weaving of layers of sand and mud collected by ancient tides. At that time, the Moon was much closer to the Earth, and its distance can be determined from the tides.

The cores must also contain records of lightning strikes, which create strong magnetic fields that imprint on the rocks. Lightning could provide an ancient ecosystem with a key nutrient by breaking apart the strong molecular bonds of atmospheric nitrogen, allowing atoms to form the compounds on which life depends.

Since the microbes that break down nitrogen today were few, if not non-existent, the frequency of impacts alone could show how much of this important nutrient was reaching the surface. “This flow of nitrogen is potentially the main component of the biosphere at that time,” says Roger Fu, a planetary scientist at Harvard University.

In many ways, the Moodies cores prepare geologists for the work ahead, when rock samples are brought back from another 3 billion-year-old terrain, the surface of Mars. NASA’s Perseverance rover will reach the Petrified River Delta later this month and begin core drilling.

If, as we hope, future Mars missions return these cores to Earth, then the laboratory techniques used on the BASE cores will come in handy, says Bosak. “By looking at these well-preserved deposits on Earth, we can learn what the ideal case would be on Mars.”

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