Meteorite strikes made life on Earth possible as they delivered large amounts of water, carbon and volatile substances to our planet, scientists claim
- Experts measured selenium isotopes in rocks that formed inside Earth’s mantle
- These rocks have been brought to the surface by plate tectonic processes
- They have remained unchanged since the early formation of the planet
- These isotopes matched meteorites from the edge of the solar system
Chemicals buried in rocks early in our planet’s history offer more proof that meteorite strikes made life on Earth possible, experts say.
Researchers studied isotopes of Selenium – atoms of the element that have the same number of protons and electrons but different numbers of neutrons.
Identical isotope signatures were found in these rocks and in certain types of meteorites.
That suggests selenium, as well as large amounts of water and other building blocks for life, originated outside our own world.
Some scientists go further with the theory of Panspermia, which suggests life itself spread across universe in the form of bacteria hitchhiking on comets or meteorites.
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Chemicals buried in rocks early in our planet’s history offer more proof that meteorite strikes made life on Earth possible, experts say (stock image)
WHEN DID BUILDING BLOCKS FOR LIFE ARRIVE ON EARTH?
Scientists say it’s hard to say exactly when the selenium and other chemicals arrived on Earth, but estimate it could have been between 4.5 and 3.9 billion years ago.
Strictly speaking, there shouldn’t be any selenium in the Earth’s mantle, they say, and no evidence of selenium has been in the Earth’s outer layer, the crust.
‘It is attracted to iron,’ said Dr Varas-Reus. ‘That is why, in the early history of our planet, it went down into the iron-rich core.
‘The selenium found in the Earth’s mantle today must have been added after the formation of the Earth’s core, at the last moment of the formation of the Earth, after our moon had also formed.’
Researchers from the Tübingen University’s isotope geochemistry group in Germany used a new technique to detect the selenium isotopes.
The research team took samples of mantle rocks, which have been brought to the surface by plate tectonic processes and remained unchanged since the formation of the Earth.
They measured that the isotope signature of the selenium in these rocks and found they matched meteorites from the edge of the solar system.
According to their calculations, around 60 per cent of the water on Earth today comes from meteorites in this region.
That is the only way oceans could have eventually formed, they say.
Volatile substances from the meteorites also contributed to the formation of the earth’s protective atmosphere.
‘This created the conditions for life on Earth to develop in its present form, said researcher Dr María Isabel Varas-Reus.
Researchers studied isotopes of Selenium – atoms of the element that have the same number of protons and electrons but different numbers of neutrons (stock image
It has been possible for some time now to measure selenium isotopes in high concentrations – in samples from rivers, for example.
However, the selenium concentration in high-temperature rocks – such as those that formed in the mantle – is very low.
Samples must be dissolved out at high temperatures, and selenium is volatile, which means the process to measure it can damage it.
The team’s new technique makes it possible to measure selenium isotopes in these high-temperature formation rocks.
‘We were very surprised that the selenium isotope signature of the Earth’s mantle closely matched a certain type of meteorite from the outer solar system,’ Dr Varas-Reus said.
‘These are carbonaceous chondrites from the solar system beyond the asteroid belt, from the area of the planets Jupiter, Saturn, Uranus and Neptune.’
The full findings of the study were published in the journal Nature Geoscience.
WHAT IS PANSPERMIA?
Panspermia is a theory that suggests life spreads across the known physical universe, hitchhiking on comets or meteorites.
Extremophiles, capable of surviving the inhospitable conditions of space, could become trapped in debris that is ejected into space after collisions between asteroids and planets that harbour life.
These dormant life-forms may then travel for an extended amount of time before colliding randomly with other planets.
One argument that supports the panspermia theory is the emergence of life soon after the heavy bombardment period of earth, between 4 and 3.8 billion years ago.
During this period, researchers believe the Earth endured an extended and very powerful series of meteor showers.
However, the earliest evidence for life on Earth suggests it was present some 3.83 billion years ago, overlapping with this bombardment phase.
These observations suggest that living things during this period would have faced extinction, contributing to the idea that life did not originate on Earth.
The idea of directed panspermia suggests lifeforms were deliberately sent out through the universe by intelligent civilisations.
Professor Francis Crick, one of the biologists who discovered the structure of DNA, examined the possibility of this in a paper in 1973.
However, Professor Crick and his colleagues concluded that the scientific evidence was ‘inadequate at the present time to say anything about the probability’.