Plate tectonics that control the movement of the continents and cause earthquakes first formed 2.5 BILLION years ago, scientists claim
- Exactly when plate tectonics began has long been a subject of geological debate
- Previous estimates for its emergence have ranged from 3.5–1 billion years ago
- Researchers analysed Earth’s past heat flow as recorded by metamorphic rocks
- They used this to determine when plate tectonics started as the Earth cooled
Plate tectonics, the gradual drift of continents across the Earth’s surface that causes earthquake, began around 2.5 billion years ago, a new study suggests.
Exactly when the Earth’s plates formed and began moving has long been a subject of debate, with estimates ranging from 3.5–5 billion years ago.
Researchers studied metamorphic rocks from across the globe to build up a picture of how the heat flow in the Earth’s crust has changed over time.
From this they were able to determine when plate tectonics must have first begun.
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Plate tectonics — the gradual drift of continents across the Earth’s surface that causes earthquakes — began around 2.5 billion years ago, a new study suggests. Pictured, the configuration the Earth’s major tectonic plates in the present day
To assess when Earth’s plate tectonics kicked off, geologist Robert Holder of the Johns Hopkins University in Baltimore and colleagues studied metamorphic rocks from 564 sites across the globe that date back as far as 3 billion years ago.
Metamorphic rocks are those that form when other types of rock — those made from sediments, or that cooled out of lava or magma — are altered through either extreme temperatures or pressures.
By analysing these rocks, the team could determine the depths and temperatures at which they were formed, building up a picture of the changing heat flow at different places across the Earth’s crust — and, in turn, the plate tectonics that controls such.
‘Some geologists consider that Earth has had plate tectonics throughout its four-and-a-half-billion-year existence,’ said paper author and Curtin University geologist Tim Johnson.
‘Whereas others consider that plate tectonics appeared abruptly some one billion years ago.’
‘Using a simple statistical analysis of the temperature, pressure and age of metamorphic rocks, we have revealed that plate tectonics evolved gradually over the past 2.5 billion years as our planet slowly cooled.’
A large focus of the researchers’ analysis concerned the so-called Proterozoic Eon, the period from 2.5–0.54 billion years ago — over half of the Earth’s history.
‘There is debate as to whether the plate tectonic processes we observe today can be used to interpret really ancient rocks or if Earth’s tectonic processes were fundamentally different in the deep geological past,’ Dr Johnson said.
Exactly when the Earth’s plates formed and began moving has long been a subject of debate, with estimates ranging from 3.5–5 billion years ago. Pictured, the changing configuration of the continents over time, dating back to 225 million years ago and the supercontinent Pangaea
‘Understanding how the ancient Earth was different to the modern Earth is key to accurately interpreting how Earth’s rocks formed,’ said Dr Johnson.
This, he adds, explains ‘why they are distributed across the continents in the patterns that we see, including where mineral resources occur, how extensive they might be, and where additional resources might be found.’
‘The framework for much of our understanding of the world and its geological processes relies on plate tectonics,’ agreed Dr Holder.
The full findings of the study were published in the journal Nature.
WHAT ARE TECTONIC PLATES?
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.