We Owe Our Lives to 3-Billion-Year-Old Stromatolite Fossils

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What’s the most impressive fossil you ever saw? For most people — those who aren’t paleontologists — the answer would probably veer towards the A-list of ancient creatures: dinosaurs, pterosaurs and other long-extinct megafauna whose size and majesty have made them the showpieces of museums and the inspiration of film franchises for decades. But what if someone told you that you’ve been overlooking the real rock stars of the fossil record for all these years? What if there was a type of creature that was much, much older than the dinosaurs, whose presence on Earth literally changed the future of the planet? And what if you knew that somewhere in the world, living examples of this ancient life form still exist — and you could visit them if you wanted to? Now that’s impressive. And that’s what you get with stromatolites. Stromatolite Fossils Stromatolites weren’t one distinct creature, but many — they’re formed by colonies of cyanobacteria, microscopic organisms that use photosynthesis to sustain themselves. Living mostly in water, the colonies that made stromatolites were somewhat sticky, thanks to a compound they secreted, which caused sediment to build up around the cyanobacteria. Read More: Minerals Reveal a New Understanding of Original Life on Earth Over time, stromatolites would accumulate multiple layers of sediment (stromatolite comes from the Greek words that literally mean layered rock), although they could form in different shapes – some flat, some round, some mushroom-shaped or mound-like. But they did more than just provide sticky places for dirt and rock to settle. Here are a few facts worth knowing about stromatolites:  Cyanobacteria Stromatolites Once Ruled the Planet Long before any kind of creatures walked the Earth, in a time that predates even the existence of marine or plant life, stromatolites were already here. Billions of years ago, our young planet, once too hot and its surface too molten to harbor life, had begun to cool. This allowed the first oceans to form. Earth was still not a hospitable place, but simple bacteria could survive and form colonies that would become stromatolites. For at least two billion years, these sticky little cyanobacteria stromatolites were the dominant life form on Earth.      When Did Stromatolites Appear on Earth? Stromatolites predate the dinosaurs by a wide margin. Not only were they once the primary form of life here, as bacteria they are also the oldest known life on Earth and are found in the oldest fossils ever discovered. Evidence of their existence stretches back as much as 3.5 billion years, to an almost unimaginably remote time known as the Archean Eon.  Read More: What Are the Oldest Fossils in the World? Back then, Earth was nothing like it is now. Were you to visit it during Archean times, you wouldn’t last long: The atmosphere of the planet then was a mix of gasses like carbon dioxide, methane and ammonia, among others, that would have been toxic to Earth’s current inhabitants. But that wasn’t the case for stromatolites, of course. They thrived in this environment, even as they were slowly changing it.  Why Are Stromatolites Important? In fact, most of life as we know it would never have developed on earth without those tireless little cyanobacteria colonies. Thanks to the wonders of photosynthesis, stromatolites in their billions were busily absorbing sunlight, water and carbon dioxide while pumping out tiny bubbles of oxygen into the world’s oceans. That doesn’t sound like much of a task, but the stromatolites of early Earth kept at it long enough that, over the eons, the oceans became saturated with oxygen. Eventually, this critical gas began to be released into the atmosphere, creating an environment that would support more complex forms of life, including the dinosaurs and, eventually, us. But long before that happened, roughly one billion years ago, stromatolites began to disappear from the fossil record. Multiple theories abound, but researchers believe that changes in the chemical composition of the world’s oceans, or perhaps the rise of more complex life that consumed cyanobacteria, were probably responsible for wiping out most stromatolites. Most, but not all. Are Stromatolites Alive? If someone told you that you could hop on a plane and visit a herd of living dinosaurs, you’d go, right? Well, if you’re so inclined, you can actually see colonies of living stromatolites for yourself. To date, scientists know of a few locations around the world where stromatolites can still live — generally, they require very salty and sheltered water environments. One of the most famous destinations — famous among stromatolite fans, anyway — is Western Australia’s Hamelin Pool Marine Nature Reserve. Australia is also home to an even rarer form of cave-dwelling stromatolite. Other living stromatolites have also been found in the Bahamas and Mexico, among a few other places. The ecosystems that stromatolites require to thrive are delicate and most of these rare enclaves of living fossils are under threat. What Do Stromatolites Look Like? Unless you’re prepared to be philosophical about the experience, you might be a little underwhelmed at your first sight of a living stromatolite. They’re not visually exciting, since they tend to look a lot like wet mats or weirdly shaped rocks. Seeing a bunch of live stromatolites wouldn’t have quite the adrenaline-inducing sense of adventure that you might feel if it were possible to visit, say, a herd of stegosauruses or a pack of velociraptors. But at least stromatolites won’t try to trample or eat you. Instead, those unassuming piles of sediment and bacteria will just keep doing what they’ve been doing for billions of years: pumping out more oxygen and storing more carbon, generally making the world a more hospitable place for creatures like us. You’re welcome! Read More: Life on Earth May Have Started with a Dose of Poison

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