Mushrooms may have helped bring the planet out of its ‘snowball’ phase

Falling rocks in tropical rocks were among the first clues that something strange happened on planet Earth.

Dropstones are rocks that land on the seabed, sometimes with such force that the sediments deform. But there shouldn’t be any falling rocks in those rocks. Glaciers are the most common source; the bellies of ice caps pick up rocks like ticks, then throw them back when they take to the sea. . Surely there couldn’t be glaciers in the tropics, could there? To the right?

In 1989, California Institute of Technology geologist Joe Kirschvink looked at this and other evidence that had been circulating for a few decades and came up with a new hypothesis: the snowball Earth. The idea is that our planet was once completely covered in ice until a kilometer thick about 650 to 700 million years ago. Surface temperatures everywhere were well below zero, and life, whatever simple form it then took, had to cope.

And the evidence suggests that this disaster happened around this time not once, but twice. The first burial seems to have lasted about 58 million years, which I feel compelled to point out is more than 24 times longer than T. rex existed (barely 2.4 million years). The second snowball, 10 million years later, lasted another 5-15 million years. Although partial glaciations would creep into the temperate zone on a regular schedule hundreds of millions of years later, near our time, as far as we know, ice would never consume the Earth again.

A study of new Chinese fossils published in January adds an interesting detail: Cave fungi may have helped pull the planet out of the second snowball. If true, that would also be remarkable because the earliest agreed terrestrial fungal fossils date to more than 200 million years later.

If you accept that the planet was frozen, it follows that once all that heavy ice melted, the uncharged earth bounced back and was bathed in cool air. Rainwater falling on new bare rock weathered the surface but also seeped into the cracks, creating caves.

It is inside what they claim are the remains of these cavities in the Ediacaran Doushantuo rock layers of China that scientists reported in Nature Communication in January they found both cave formations and fossilized filaments of pyrite that look like – and I agree – very much like mushrooms.

There are curved filaments that branch and merge – including A- and H-shaped structures – and small branch buds that sometimes seem to seek each other out; hollow spheres alone or in chains (spores?) both embedded in filaments and at their ends; and two different fiber gauges, involving at least two species. The fibers also lack inner walls called septa which often divide these tubes into cells.

Several types of fungi today possess this exact suite of characters, while no other group of organisms do, say the authors. Moreover, the curved and bent filaments seem to exclude any abiotic look-alikes. Studies of physical fungal fossil imposters show that they are uniformly broad, while true fungi tend to be narrower and can be many sizes.

Outside evidence suggests that a fungal interpretation is plausible. Molecular clocks, which use calculated DNA mutation rates to estimate when various groups of organisms evolved, suggest fungi could be between 0.9 and 1.5 billion years old.

The authors hypothesize that soon after the cavities formed, structures such as stalagmites, stalactites and grape-shaped botryoids covered their walls, colonized and catalyzed by fungi and other microorganisms. ; large spheres in the fossils penetrated by the filaments could be some kind of symbiont or food. Notably, modern cave formations carry similar microbes, including fungi that resemble the fossils.

Modern fungi are known for the ability of some to mine rock and extract nutrients. If the pockets of moldy rock in freshly snowballed Earth were geographically widespread, such life would have accelerated the weathering of continental rocks already underway on the surface and the delivery of phosphorus, a fertilizer, into the ocean. The resulting algal blooms would have pumped oxygen into the air. Notably, atmospheric oxygen levels appear to have been much lower than today before the Earth snowball.

It wouldn’t be long before life forms capable of capitalizing on all this new, free redox power seized the opportunity, an event called the Cambrian Explosion. Before Earth’s snowball, the most complex life – and the sum total of more than 3.5 billion years of evolution – appears to have been a sponge. After the Earth Snowball, Titanosaurs and Dawn Redwoods and Gigantic Mushrooms appear. Was there a connection, and did it involve all that extra oxygen? It is a subject of active research.

More generally, the fact that we only recently realized that our planet probably went through a Mr. Freeze phase of 58 million years is troubling as much for what it implies about what we don’t know as what we do. I once heard a lecture from a classic who claimed that, given the pitiful nature of the remaining evidence, what we know about the ancient human world is akin to what might be discovered about the castle of Versailles looking through a keyhole.

The same could be said of paleontology, especially the paleontology of life before bones and shells, or the geology of the Earth in distant and alien conditions. Geologist Paul Hoffman told that after Joe Kirschvink first developed the snowball hypothesis and shared it with him, it took them a while to do anything. either about it because such a scenario was so different from Earth’s known history that they had no idea. particular piece of evidence in the rock record was for or against.

And if discerning major events in Earth’s history has proven difficult where we have a rock record, what else don’t we know about our planet’s history and owner’s manual because the rocks concerned do not survive or are not currently on the surface? For example, much of the Earth appears to be missing a frighteningly important billion-year-old chunk of the geologic record, a glaring omission that geologists somewhat ominously call the Great Unconformity. They wonder why he’s missing, but the simple fact that he is lack worries me more. It’s like the Earth has been on a bender for 25% of its lifespan and “completely doesn’t remember” what happened or where its keys are.

So we should be grateful for the memories that our planet has. Dropping stones and rock pockets paint a vivid picture if the interpretations given here are correct: a Europa-like planet metamorphosing into a freshly scraped collection of weathered continents filled with moldy caves, quietly fertilizing the oceans and oxygenating the atmosphere just before the biggest explosion of life the planet would ever see.

This is an opinion piece and analysis; the opinions expressed by the author or authors are not necessarily those of American scientist.

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