Harvard scientists find proof that Earth's plate tectonics date back at least 3.25 billion years ago
The Earth's crust was pushing and tugging like present plate tectonics at least 3.25 billion years ago, according to new research published today (Oct .24) in PNAS, which examined fragments of the most ancient rocks on the planet.
The research also offers the oldest evidence of the moment when the planet's magnetic north and south poles switched places.
The two findings provide hints as to how such geological changes may have produced a planet with a more favorable environment for the emergence of life.
Geologists explored a portion of one of the oldest and most stable pieces of the Earth's crust
The study was conducted by Harvard geologists, Alec Brenner and Roger Fu, and focused on a region of western Australia's Pilbara Craton, one of the oldest and most stable portions of Earth's crust.
Using innovative methods that combined magnetometers, demagnetizing tools, and the Quantum Diamond Microscope, the researchers could figure out how, when and which direction the crust shifted- as well as the magnetic influence originating from Earth's magnetic poles.
They found that some of the Earth's oldest surface was shifting at a rate of 6.1 centimeters (cm) per year and 0.55 degrees every million years.
Researchers argue that the speed and direction of ancient crust movement are evidences for early plate tectonics
In a prior investigation, the same researchers found that the ancient crust was moving much slower than this- with the latest study being more than twice as fast. The researchers argue that plate tectonics is the most logical and compelling explanation for the speed and direction of this latitudinal movement.
"There's a lot of work that seems to suggest that early in Earth's history, plate tectonics wasn't actually the dominant way in which the planet's internal heat gets released as it is today through the shifting of plates," said Alec Brenner in a press release. Brenner is one of the paper's lead authors and a Harvard's Paleomagnetics Lab member.
"This evidence lets us much more confidently rule out explanations that don't involve plate tectonics."
A 3.2 billion-old magnetic field steady and powerful enough to support life
The researchers also discuss what they consider to be the earliest proof that Earth's geomagnetic fields were reversed, flipping the positions of the magnetic North and South Poles.
According to NASA, the pole has reversed 183 times in the last 83 million years and maybe several hundred times in the last 160 million years, making this type of 'flip-flop' typical throughout Earth's geologic history.
The reversal reveals a lot about the magnetic field of the planet 3.2 billion years ago. The magnetic field was probably steady and powerful enough to prevent solar winds from degrading the atmosphere. This understanding, along with the findings on plate tectonics, provides hints as to the conditions in which the earliest forms of life originated.
A brief review of Earth's plate tectonics
Currently, the Earth's crust is made up of around 15 movable plates that support today's continents and oceans. Long ago, as the plates migrated toward and away from one another, they created new mountains, continents, and rocks that were exposed to the atmosphere.
These new rocks then underwent chemical reactions that stabilized the Earth's surface temperature over billions of years.
The oldest crustal fragments are forced into the inner mantle and never come to the surface, making it difficult to gather evidence of when plate tectonics began. Therefore, no rock is older than around 4 billion years, and just 5 percent of all rocks on Earth are older than 2.5 billion years.
Overall, the latest study contributes to the expanding body of knowledge showing tectonic movement began relatively early in Earth's 4.5 billion-year history. It also supports the idea that the earliest living forms on Earth evolved in a more moderate environment.
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