The Earth’s surface is a place of turbulence. Mountains rise, continents coalesce and break apart, and earthquakes shake the ground. All of these processes occur as a result of plate tectonics, the movement of huge chunks of the Earth’s crust.
This movement may be the reason why life exists here. Earth is the only planet known to have plate tectonics and the only planet known to have life. Most scientists think it’s no coincidence. Plate tectonics pulls carbon from the planet’s surface and atmosphere and stabilizes its climate by dragging huge chunks of the Earth’s crust into the Earth’s middle layer, the mantle. It also pushes life-giving minerals and molecules to the surface. All of these factors add up to create a place where life thrives, from the depths of the ocean to the towering peaks.
But researchers don’t know when or why plate tectonics began, making it difficult to determine how important this process was to the evolution and diversification of life. Some believe that plate movement began 700 million years ago, when simple multicellular organisms already existed. Some believe that when the Earth’s plates first cracked, only single-celled organisms reigned supreme.
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In fact, new methods are allowing scientists to look deeper into the past than ever before, leading some to argue that plate tectonics emerged shortly after Earth’s formation, perhaps even before life itself. If true, this hypothesis could suggest that even the most primitive life evolved on active planets, which could make plate tectonics an essential element in the search for extraterrestrial life. It means something.
“The only way we can reliably see long-term history is by being on our planet,” said Jesse Reimink, a geoscientist at Pennsylvania State University who studies early Earth history. “Before we can do much with exoplanet data, we need to really understand the life cycles of planetary bodies.”
destruction of evidence
Only Earth has jigsaw-like tectonic plates that collide and break apart like bumper cars. Other rocky planets in the solar system have a single hard crust. This is a geological arrangement that scientists refer to as “stagnant lid” or “single lid” tectonics.
In plate tectonics, a pancake-like brittle mass of crust and upper mantle rests on a hotter, more mobile mantle below. New crust forms at mid-ocean ridges, where gaps between separating plates create space for magma from the mantle to rise. Geological balancing forces rupture the dense oceanic crust at subduction zones, where one plate slides beneath the other. The oldest known oceanic crust in the Mediterranean Sea is only 340 million years old, too young to pinpoint when plate tectonics occurred.
A crack along the ridge of two plates moving away from each other at Krafla in northeastern Iceland.
Michele D’Amico supersky77/Getty Images
Continental crust is lighter than oceanic crust and floats above the destruction caused by subduction. But still, very few remains of Earth’s early days remain, and what remains is eroded and distorted. Today, less than 7% of the rocks on Earth’s surface are older than 2.5 billion years. 4.03 billion years ago, as far back as the Hadean period, the rock record completely disappeared. During the first 500 million years of Earth’s existence, not a single piece of basalt remained.
Because of this constant planetary recycling, the oldest indisputable evidence of plate tectonics – rocks formed exclusively in subduction zones – dates back only about 700 million years. Another strong piece of evidence is a section of oceanic crust pushed up above continental crust at the start of subduction, which emerged globally about 900 million years ago. During this geological period, multicellular animals such as sponges and comb jellies were just emerging.
Some geoscientists believe that plate tectonics has only been in operation since then. However, it is more likely that plate tectonics appeared earlier, during the Archean era, which lasted from 4 billion to 2.5 billion years ago. Evidence is primarily based on chemical analysis of rocks. For example, around 3 billion years ago, there are indications that an increasing amount of Earth’s crust was melting and reforming, rather than forming directly from mantle rocks. About 3.8 billion years ago, chemical changes in Earth’s oldest minerals suggest a change from a stable, long-lived crust to a short-lived, more modern-looking crust, possibly marking the beginning of subduction. It is thought that. Although there is no single agreed-upon date, the Archean era looks promising as a time when major geological changes were occurring on Earth.
“This represents a very important transition,” said Nadja Drabon, an Earth and planetary scientist at Harvard University who led the study showing a transition to a short-lived crust.
a handful of sand
Whenever tectonics began, geoscientists agree that it probably helped drive the evolution and complexity of life.
“There may be billions of planets with some form of primitive life, but to build radio transmitters or launch rocket ships, we need plate tectonics and ocean-to-ocean systems. “We need certain conditions that are only likely to occur on a planet’s continent,” Robert Stern, a geoscientist at the University of Texas at Dallas, told Live Science.
In prehistoric animals, plate tectonic activity is associated with faster rates of evolution, likely because geological movements fragment habitats and create new niches for life to evolve. Possible.
Past research suggests that coelacanth evolution was likely driven in part by plate tectonics.
Plate tectonics may also have allowed life to recover from catastrophic mass extinctions. For example, at the end of the Permian period, a mass extinction caused by carbon dioxide-spewing volcanic eruptions wiped out 90% of Earth’s species. Weathering of continental rocks breaks down carbon-containing minerals and washes them into the ocean, where marine life converts them into coral reefs and shells, which become limestone and eventually sink into the planet’s interior. life was eventually restored. When the atmosphere deteriorates, tectonics gradually restores the Earth to a habitable environment.
Although almost all geoscientists agree that without plate tectonics, life on Earth might be limited to primitive organisms, a small group of researchers now believe that plate tectonics They suggest that they may have appeared even earlier, perhaps contributing to the origin of life itself. It transports the minerals that support life from the Earth’s interior to the Earth’s crust.
This is difficult territory, pushing researchers back 4 billion years, or before the Hadean period. The only direct evidence for the first 500 million years of Earth’s existence is the presence of zircon, a mineral that survives melting at the temperatures and pressures of the mantle. The rocks that once contained these minerals have melted away, but zircon, which is smaller than a grain of sand, remains.
“They’re so small that we’re just throwing the kitchen sink at them, trying to get every little bit of information we can from them,” Drabon told Live Science.
These zircons from the Hadean period are sparse. Anything found in the world could fit into a thimble. But this handful of studies shows that Earth had oceans 4.4 billion years ago, just 200 million years ago after the planet formed, and shortly before the ancestors of all life today existed. Masu. Research published in June shows that as early as 600 million years after Earth’s formation, Earth had both land and fresh water.
For some researchers, this suggests that the Earth’s crust may have been recycled during the Hadean period. Atsushi Korenaga, a geophysicist at Yale University, said water weakens the Earth’s crust, creating the potential for rupture and subduction. Plate tectonics requires water, which begs the question, “If we have surface water, why don’t we have plate tectonics?” Korenaga said.
In an experimental study published in 2023, researchers found that melting rocks under high pressure and conditions that mimic subduction produced rocks similar to Earth’s oldest rocks. Korenaga also said that plate tectonics was the only effect that reduced the amount of carbon dioxide in early Earth’s atmosphere from the levels seen on Venus to the more moderate concentrations that existed by the beginning of Earth’s Archean era. It is claimed to be a method.
Interestingly, another important event occurred during the Hadean period that made Earth distinctly different from its rocky neighbors. Approximately 100 million years after the Earths first coalesced, a planet-sized object collided with the Earth, completely shattering and melting both objects and spewing Earth-destroying material. It’s going to be the moon. A paper published earlier this year modeled the collision and found that the mixing of the two objects created a plume of hot material in Earth’s mantle, which may have triggered subduction after about 200 million years. .
“Why is Earth the only rocky planet with plate tectonics?” said Qianyuan, lead author of the paper and a postdoctoral fellow in geodynamics at the California Institute of Technology. “I think the giant impact that formed the moon could be the main factor.”
But not everyone is convinced by this story. The beginning of Hadean plate tectonics is an interesting idea, T. Mark Harrison, professor emeritus of geosciences at the University of California, Los Angeles, told Live Science, but the evidence is still fairly sparse. He worries that geoscientists on all sides of the issue are overconfident in their claims. “But the last thing we need is a new form of groupthink based on literal thimblefuls of grains of sand.” I wrote this in the article titled.
life in other worlds
If plate tectonics fuels life, or just complex life, the search for other life among stars may lead humans to geologically active planets.
Tobias Meyer, an expert on mantle mechanics at the University of Oxford, said that unfortunately it is not yet possible to detect plate tectonics on distant exoplanets. But in 2021, Meyer and his team used thermal data and computer modeling to find that the rocky exoplanet LHS 3844 b, 49 light-years from Earth, has an active mantle and a shifting crust. I discovered that there is a gender.
Researchers suspect that the exoplanet LHS 3844b, located 49 light-years from Earth, also has plate tectonics.
NASA, ESA, CSA, DANI Player (STScI))
LHS 3844 b is unlikely to harbor life. It orbits very close to the star and has no atmosphere. Half of the Earth is exposed to daylight and has temperatures of 1412 degrees Fahrenheit (767 degrees Celsius), while the other half experiences frigid temperatures of -429 degrees Fahrenheit (-273 degrees Celsius) at night. Meyer and colleagues reported in 2021 that it is this temperature difference between the two sides of the planet that drives LHS 3844 b’s mantle motion. If true, that version of plate tectonics bears no resemblance to Earth’s. But it does illustrate the diversity of planetary geology that may be lurking elsewhere in the universe.
“Ultimately, understanding the causes of tectonics and whether they operate on different planets will help us understand whether these planets are habitable or not,” Meyer said.
More powerful telescopes like the James Webb Space Telescope could lead to better hints at the geology of exoplanets in the near future. But Earth’s neighbors also deserve scrutiny, says Craig O’Neill, a geophysicist at Australia’s Queensland University of Technology. Venus is right next door, but whether or not it has experienced tectonic movements in the past is still debatable. Understanding the current monolithic geology could help scientists understand why the fates of the two planets diverged and why one planet likely harbors life and the other does not. This could help clarify whether plate tectonics can explain this phenomenon.
“A lot of the future developments in plate tectonics will come from looking up rather than navel gazing,” O’Neill told Live Science.
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