How did the building blocks of life on earth – amino acids, lipids, carbohydrates and nucleic acids – begin to form? They are the fundamental molecules making up all life and had to have come from somewhere.
New research shows how iron-rich particles from meteors OR volcanoes about 4.4 billion years ago, could have provided the right conditions for the formation of these molecules, essential in the origins of life on our planet.
Read more: Multi-celled animals may have evolved thanks to “wildly fluctuating” oxygen levels a billion years ago
It has long been a subject of debate as to where the precursors of organic molecules – the chemical compounds that make up every living cell on Earth – came from.
Previous studies have suggested that these precursors – hydrocarbons, aldehydes and alcohols – may have come to Earth from space through asteroid and comet collisions, billions of years ago.
But others suggest an alternative route – that these precursors emerged in the oceans and atmosphere of the early Earth through chemical reactions promoted by high energy during lightning, volcanic activity, or impacts.
Little observable evidence remains of conditions on Earth more than four billion years ago.
This period of Earth’s history is dubbed the “Hadean,” a period when the planet was still extremely hot, had intense volcanic activity, and suffered frequent collisions with other objects in the solar system.
The geological eon begins with the planet’s formation about 4.54 billion years ago and ends about 4.0 billion years ago.
Researchers from the Ludwig-Maximilians-Universität München and Max Planck Institute for Astronomy in Germany investigated how life-forming molecules may have formed in the Hadean. They simulated a large range of conditions, that previous research suggests may have existed on early Earth, to assess the likelihood of different chemical reactions taking place.
Both meteorite (space-born) or ash (Earth-born) particles that might have been deposited on volcanic islands were tested to see if, in these conditions, they could have promoted the conversion of carbon dioxide in the atmosphere into the precursor molecules for organic life.
Carbon dioxide gas placed in a heated and pressurised autoclave system was subjected to pressures between nine and 45 bar. For comparison, atmospheric pressure at sea level today is 1.013 bar while on Venus (which probably resembles Hadean Earth in many ways) it is 93 bar.
Temperatures were also varied from 150°C to 300°C. Wet conditions were compared to dry conditions by adding hydrogen gas or water respectively.
Crushed samples of iron meteorites, stony meteorites and volcanic ash were added to the system, as well as minerals that may have been present on early Earth.
Iron-rich particles from meteorites and volcanic ash were found to promote the conversion of carbon dioxide into hydrocarbons, aldehydes and alcohols.
Read more: First complex ecosystems formed in Ediacaran – millions of years earlier than thought
The results suggest that hydrocarbons formed at 300°C and alcohols and aldehydes formed at lower temperatures when the atmosphere would have cooled over time. These compounds may then have undergone further reactions to form sugars, carbohydrates, fat molecules, amino acids, DNA and RNA.
The scientists estimate that their proposed mechanism could have synthesised up to 600,000 tonnes of organic precursor molecules per year on early Earth.
But which was it? Did volcanoes on Earth, or meteors from space spark the beginnings of life on our planet?
In a paper published in the journal Scientific Reports, the authors of the research say, “it is difficult to deduce with certainty which scenario was the most dominant (if any) due to missing key data.” This new study shows that it could have been a little bit of both.
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