Privileged Planet: plate tectonics explained (Introduction)

by David Turell , Friday, June 08, 2018, 20:05 (2360 days ago) @ David Turell

A very long thorough article on how important it is to start and maintain life:

https://www.quantamagazine.org/plate-tectonics-may-be-essential-for-life-20180607/

"But there’s more to plate tectonics than earthquakes and eruptions. A wave of new research is increasingly hinting that Earth’s external motions may be vital to its other defining feature: life. That Earth has a moving, morphing outer crust may be the main reason why Earth is so vibrant, and why no other planet can match its abundance.

“'Understanding plate tectonics is a major key to understanding our own planet and its habitability. How do you make a habitable planet, and then sustain life on it for billions of years?” said Katharine Huntington, a geologist at the University of Washington. “Plate tectonics is what modulates our atmosphere at the longest timescales. You need that to be able to keep water here, to keep it warm, to keep life chugging along.”

"In the past few years, geologists and astrobiologists have increasingly tied plate tectonics to everything else that makes Earth unique. They have shown that Earth’s atmosphere owes its longevity, its components, and its incredibly stable Goldilocks-like temperature — not too hot, but not too cold — to the recycling of its crust. Earth’s oceans might not exist if water were not periodically subsumed by the planet’s mantle and then released. Without plate tectonics driving the creation of coastlines and the motion of the tides, the oceans might be barren, with life-giving nutrients relegated forever to the stygian depths. If plate tectonics did not force slabs of rock to dive underneath one another and back into the Earth, a process called subduction, then the seafloor would be entirely frigid and devoid of interesting chemistry, meaning life might never have taken hold in the first place. Some researchers even believe that without the movement of continents, life might not have evolved into complex forms.

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"In December 2015, researchers in Australia published a study of roughly 300 drill cores from seafloor sites around the globe, some containing samples that were 700 million years old. They measured phosphorus as well as trace elements like copper, zinc, selenium and cobalt — nutrients that are essential for all life. When these nutrients are abundant in the oceans, they can spark rapid plankton growth. The researchers, led by Ross Large of the University of Tasmania, showed that these elements increased in concentration by an order of magnitude around 560 to 550 million years ago.
Large and his team argue that plate tectonics drove this process. Mountains form when continental plates collide and shove rock skyward, where it can more readily be battered by rain. Weathering then slowly leaches nutrients from the mountains into the oceans.

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"Tectonic activity also plays an essential role in maintaining the long-term stability of Earth’s thermostat. Consider the case of carbon dioxide. A planet with too much carbon dioxide could end up like Venus, a planetary blast furnace. Plate activity on Earth has helped to regulate the level of carbon dioxide over the eons.

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"According to research published in 2016, plate tectonics then initiated a two-step process that led to higher oxygen levels. In the first step, subduction causes the Earth’s mantle to change and produce two types of crust — oceanic and continental. The continental version has fewer iron-rich rocks and more quartz-rich rocks that don’t pull oxygen out of the atmosphere.

"Then over the next billion years — from 2.5 billion years ago to 1.5 billion years ago — rocks weathered down and pumped carbon dioxide into the air and oceans. The extra carbon dioxide would have aided algae, which then could make even more oxygen — enough to eventually spark the Cambrian explosion.

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"According to these theories, plate tectonics may have started and stopped several times before picking up momentum about 3 billion years ago. “If you had to press everyone’s buttons and make them take a number, there’s a running ballpark in the community that around 3 billion years ago, plate tectonics started emerging,” O’Neill said.

"Yet it’s hard to know for sure because the evidence is so fragmentary.

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"O’Neill has come to think of plate tectonics as a middle-age phase for rocky planets. As a planet ages, it may evolve from a hot, stagnant world to a warm, tectonically active one, and finally to a cold, stagnant one again in its later years. We know planets can grow quiet as they cool down; many geologists think this is what happened to Mars, which cooled off faster than Earth because it is so much smaller."

Comment: Huge article worth reading all. Earth looks especially designed for life.