Jakarta –
Before hosting life as it does now, Earth was once a planet that was not suitable for living creatures to live on. For our planet’s first 50 million years, about 4.5 billion years ago, its surface was a sea of super-hot magma, bubbling and emitting heat from within the Earth.
The cooling of planet Earth from its molten state, and the crystallization of magma oceans into solid rock, were decisive stages in the formation of our planet’s structure, its surface chemistry, and the formation of its early atmosphere.
These ancient rocks, which contain clues that may explain Earth’s habitability, are assumed to have been lost due to the breakdown of tectonic plates.
But now, a team of researchers from the University of Cambridges has found chemical remains of Earth’s magma ocean in 3.7 billion year old rocks in southern Greenland. These findings reveal an interesting picture of a time when the Earth was almost entirely liquid.
Hell on Earth
Earth is a product of a chaotic early Solar System, which is believed to have led to a number of catastrophic impacts between Earth and other planetary bodies.
The peak of Earth’s formation was its collision with an impact planet the size of Mars, which also resulted in the formation of the Moon as Earth’s natural satellite about 4.5 billion years ago.
This cosmic clash is thought to have generated enough energy to melt the Earth’s crust and almost the entire interior of our planet (Earth’s mantle), thereby creating planet-scale volumes of molten rock that formed a ‘magma ocean’ hundreds of kilometers deep.
In contrast, today, Earth’s crust is entirely solid, and its mantle allows slow, viscous geological movement, a far cry from the liquid magma of Earth’s early mantle.
“As the Earth recovered and cooled after its chaotic collision, the deep ocean of magma crystallized and solidified, starting Earth’s journey towards the planet we know today,” said Helen M Williams, Geochemist at the University of Cambridge, quoted from IFL Science.
“Volcanic gases emitted from Earth’s cooling magma ocean may have played an important role in the formation and composition of our planet’s early atmosphere, which would ultimately support life,” he said.
Geological search
Finding geological evidence of the Earth’s former liquid state is very difficult. This is because the magma ocean event likely occurred more than 4 billion years ago, and many rocks from that period of Earth’s history have been recycled by plate tectonics.
Even though rocks from this period no longer exist, their chemical traces may still be preserved in the depths of the Earth. Crystals that harden from the Earth’s cooling period will be so dense that they sink to the bottom of the Earth’s mantle.
Scientists even believe that these mineral residues may be stored in isolated zones deep within the core of the Earth’s mantle.
If they exist, these ancient crystal tombs are inaccessible to us, hidden too deep for us to sample them directly.
And if they rise to the Earth’s surface, marine magma crystals will naturally undergo a process of melting and solidification, leaving only traces of their origin in volcanic rocks that reach the Earth’s crust.
Hints of magma crystals
“We knew Greenland would be a good place to search for traces of Earth’s dark past. Our samples come from the Isua supracrustal belt in southwest Greenland, which is a well-known region for geologists,” Williams wrote.
At first glance, continued Williams, the Isua rocks look like modern basalt that we find on the sea floor. However, these rocks are among the oldest in the world, believed to be between 3.7 and 3.8 billion years old.
While analyzing the Isua rocks, researchers discovered a unique iron isotope signature. These signs indicate that the region of the mantle where these rocks were formed has experienced very high pressure, more than 700 kilometers below the Earth’s surface. That is where the minerals formed during the crystallization of the magma ocean lie.
But if these rocks do have traces of a sea of crystallized magma, how did they get to the Earth’s surface? The answer lies in how Earth’s interior melted, producing volcanic rock on the planet’s surface.
Melting rock
When regions of the Earth’s semi-solid mantle heat and melt, they rise into the Earth’s crust, ultimately producing volcanic rock when the magma reaches the surface and cools.
By studying the chemistry of rocks at the surface, we can investigate the composition of the material that melted to form them.
The isotopic makeup of the Isua rock reveals that its journey to Earth’s surface involved several stages of crystallization and remelting in the planet’s interior, a kind of distillation process on its journey to the surface.
But the emergent rocks, located in present-day Greenland, still retain chemical signatures linking them to the magma-covered Earth of the past.
“Our results provide some of the first direct geological evidence indicating the presence of magma ocean crystals in volcanic rocks found on Earth’s surface. Now, we want to understand whether other ancient volcanic rocks around the world can tell us more about Earth’s former magma oceans , or have we discovered a geological oddity,” Williams said.
According to him, if other volcanoes also spew similar geological artifacts, we might also look to modern eruption hotspots such as Hawaii and Iceland to find out new things about isotopes that reveal Earth’s past.
It is possible that more primordial rocks will be discovered in the future that could help us understand more about Earth’s magma-filled past.
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(rns/afr)
2023-12-27 02:45:18
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