The Earth’s tectonic plates started moving more than 3.2 billion years ago – just over 1.3 billion years after the Earth first formed and earlier than originally thought.
The outermost shell of the Earth is broken down into seven major tectonic plates and many smaller ones that move between 0.4 inches and 6.2 inches per year.
A team of geologists from Harvard University set out to find out just how early in the Earth’s history tectonic activity – that is plate movement – started to happen.
Rocks in Western Australia, one of the oldest pieces of the Earth’s crust, show evidence of drift of about one inch per year – starting 3.2 billion years ago.
There are a range of theories over exactly when tectonic activity started on the Earth – from as late as 1 billion years ago to 3 billion years ago – this new research puts the start of movement about 200 million years earlier than the oldest estimates.
n artistic cross-section through forming crust approximately 3-4 billion years ago. The presence or absence of plate tectonics during this time is a topic of vigorous scientific debate
The research team, led by Alec Brenner from Harvard, looked for clues of tectonic activity in ancient rocks in the more than 3 billion year old Australian rocks.
The researchers believe this shift is the earliest proof that modern-like plate motion happened earlier in the evolution of the Earth than first realised.
They also believe it shows that the ancient Earth was very similar in its structure to the world we know today.
It adds to growing research that tectonic movement occurred on the early Earth and was a lot more similar to modern movements than assumed.
Researchers studied rocks from the Pilbara Craton, an old and stable part of the continental lithosphere located in Pilbara, Western Australia.
The lithosphere is the rigid outer shell of the Earth that the plates are part of and is a mixture of ocean and continental shell – each topped by their own kind of crust.
Roger Fu, an author on the study, poses on an outcrop of the Honeyeater Basalt in Western Australia’s Pilbara Craton. The ancient rocks exposed here showed the study’s authors that the Pilbara Craton moved over the Earth’s surface some 3.2 billion years ago
‘Basically, this is one piece of geological evidence to extend the record of plate tectonics on Earth farther back in Earth history,’ said Brenner, a paper co-author.
‘Based on the evidence we found, it looks like plate tectonics is a much more likely process to have occurred on the early Earth and that argues for an Earth that looks a lot more similar to today’s than a lot of people think.’
Plate tectonics is key to the evolution of life and the development of the planet.
Today, the Earth’s outer shell consists of about 15 rigid blocks of crust housing the planet’s continents and oceans, the researchers say.
The movement of these plates shaped the location of the continents and helped form new ones – as well as unique landforms like mountain ranges.
It also exposed new rocks to the atmosphere, which led to chemical reactions that stabilized Earth’s surface temperature over billions of years.
A stable climate is crucial to the evolution of life, the team wrote.
When the first shifts occurred has long been an issue of considerable debate in geology and so any information that sheds light on it is valuable.
The study, published on Earth Day, helps fill in some of the gaps and loosely suggests the earliest forms of life developed in a more moderate environment.
‘We’re trying to understand the geophysical principles that drive the Earth,’ said Roger Fu, one of the paper’s co-authors.
He said plate tectonics is responsible for cycling elements necessary for life into the Earth and back out of it again.
It’s a process that is also helping in the understanding of other planets in the solar system and in exoplanets beyond our own star.
‘Currently, Earth is the only known planetary body that has robustly established plate tectonics of any kind,’ said Brenner, from the Graduate School of Arts and Sciences.
‘It really behooves us as we search for planets in other solar systems to understand the whole set of processes that led to plate tectonics on Earth and what driving forces transpired to initiate it,’ he said.
‘That hopefully would give us a sense of how easy it is for plate tectonics to happen on other worlds, especially given all the linkages between plate tectonics, the evolution of life and the stabilization of climate.’
A geologic map of the Pilbara Craton in Western Australia. The rocks exposed here range from 2.5 to 3.5 billion years ago, offering a uniquely well-preserved window into Earth’s deep past
Members of the project team traveled to Pilbara Craton in Western Australia.
A craton is a primordial, thick, and very stable piece of crust. They are usually found in the middle of tectonic plates and are the ancient hearts of the Earth’s continents.
These features make them the natural place to go to study the Earth.
The Pilbara Craton stretches about 300 miles across, covering approximately the same area as the state of Pennsylvania.
In 2017, Fu and Brenner took samples from a portion called the Honeyeater Basalt by drilling into the rocks and collected core samples about an inch wide.
Fu and Brenner’s work differs from most studies because the scientists focused on measuring the position of the rocks over time while other work tends to focus on chemical structures in the rocks that suggest tectonic movement.
Researchers used the novel Quantum Diamond Microscope to confirm their findings from 3.2 billion years ago.
The microscope images the magnetic fields and particles of a sample. It was developed in collaboration between researchers at Harvard and MIT.
In the paper, the researchers point out they weren’t able to rule out a phenomenon called ‘true polar wander.’
It can also cause the Earth’s surface to shift. Their results lean more towards plate tectonic motion because of the time interval of this geological movement.
The research has been published in the journal Science Advances.
The Earth is moving under our feet: Tectonic plates move through the mantel and produce Earthquakes as they scrape against each other
Tectonic plates are composed of Earth’s crust and the uppermost portion of the mantle.
Below is the asthenosphere: the warm, viscous conveyor belt of rock on which tectonic plates ride.
The Earth has fifteen tectonic plates (pictured) that together have molded the shape of the landscape we see around us today
Earthquakes typically occur at the boundaries of tectonic plates, where one plate dips below another, thrusts another upward, or where plate edges scrape alongside each other.
Earthquakes rarely occur in the middle of plates, but they can happen when ancient faults or rifts far below the surface reactivate.
These areas are relatively weak compared to the surrounding plate, and can easily slip and cause an earthquake.