Asteroid impacts may have triggered the first seismic shifts on Earth more than four billion years ago.
It was previously believed that the planet was too hot to sustain plate tectonics during the Hadean Eon, but a new study challenges this assumption.
Experts have found the force of numerous smashes may have brought heated layers of rock to the surface and forced cooler material downwards.
Asteroid impacts may have triggered the first seismic shifts on Earth more than four billion years ago. Experts have found the force of numerous smashes may have heated layers of rock on the surface and forced them downwards
WHAT ARE PLATE TECTONICS?
The Earth’s surface today is made up of a rigid outer layer consisting of the crust and mantle, known as the lithosphere, which is typically about 100 km (60 miles) thick.
This overlies a more flexible layer called the asthenosphere, the upper layer of the Earth’s mantle.
The lithosphere is broken up into about a dozen large plates and several small ones.
These plates move relative to each other, typically at rates of 5 to 10 cm (2 to 4 inches) per year.
They interact along their boundaries, where the clash together, move apart, or slip past one another.
Such interactions are thought to be responsible for most of Earth’s seismic and volcanic activity.
Researchers from Macquarie University in Sydney used mathematical models to simulate the influence of large impacts on the Earth’s tectonic evolution.
Little is know about Hadean Eon, named after the mythical ancient Greek god of the underworld for the hellish conditions present during the first 500 million years of the Earth’s existence.
Some scientists believe a motionless ‘lid’ covered the planet, with moving plates developing much later.
But geologists studying the structure of ancient grains of zircon, one of the oldest surviving natural materials, have suggested that samples dating to before 4.1 billion years ago show evidence of early tectonic activity.
One possible explanation for this is impact cratering, a process that was more prevalent in the early Solar System than it is today.
This process has left a particularly visible mark on our moon, with its many pock marked craters.
It may also have kick-started subduction, or the forcing downwards of surface material, before the onset of plate tectonics as we know it.
Writing in their research paper, its authors said: ‘Impact cratering was a dominant geologic process in the early solar system that probably played an active role in the crustal evolution of the young terrestrial planets.
‘The Earth’s interior during the Hadean, 4.56 to 4 billion years ago, may have been too hot to sustain plate tectonics.
‘Our simulations show that the thermal anomalies produced by large impacts induce mantle upwellings that are capable of driving transient subduction events.
Impact cratering, a process that was more prevalent in the early Solar System than it is today. This could have kick-started subduction, or forcing downwards of surface material, before the onset of plate tectonics as we know it (artist’s impression)
‘Furthermore, we find that moderate-sized impacts can act as subduction triggers by causing localized lithospheric thinning and mantle upwelling, and modulate tectonic activity.’
The team found that energy delivered by impact events would have heated the Earth’s interior and caused plumes of material from the mantle to rise upwards.
This in turn would have driven the subduction of early Earth’s thin and weak sinking plates into the mantle.
In contrast to modern Earth’s subduction zones along tectonic plate boundaries, the simulated subduction events were occurred in very small areas over a short space of time.
This means that the Earth would have flipped from being tectonically stagnant to tectonically active, depending on the size and frequency of impacts
The full findings of the study were published in the journal Nature Geoscience.