Did life's ingredients come from space?

15 December 2017
Posted by Lewis Thomson.

The question of where life began is a difficult one to answer. While some scientists believe that life began on earth, others believe that life – or at least its building blocks – came from space. New research has uncovered how this might have happened.

Proteins are an essential part of life on earth. In fact, almost everything a cell does is dependent on them. Each protein is made up of lots of smaller parts called amino acids, and the sequence of amino acids determines what the protein does. The main role of your DNA is actually to tell your cells how to make proteins: each gene corresponds to a protein, and the sequence of DNA in the gene determines the sequence of amino acids in the protein. 

Because of the importance of proteins, amino acids are often called “life’s building blocks”. But these building blocks are quite complex molecules, with a unique structure of carbon, hydrogen, oxygen, and nitrogen atoms. Because of this complexity, there is some debate over how they formed in the first place.

Most scientists believe that they formed on Earth from simpler molecules reacting with each other, and that this then paved the way for life to begin. However, amino acids and other complex molecules have been found in comets and meteorites. This has led some scientists to believe that the building blocks for life could have originally come from space.

If this is true, there is still the question of how they formed. A team of researchers led by Michael Huels, from the University of Sherbrooke in Canada, may have found an answer.

When a comet is exposed to high levels of radiation from the star it orbits, the molecules that make up the comet can be “ionised”.  This means that their electrons are torn off, and these electrons lose some of their energy. They are then called “low energy electrons”. Michael’s team were interested in the potential role of these low energy electrons in driving further chemical reactions between the molecules.

The team created thin films of frozen methane and oxygen, similar to those that can be found on the surface of comets. They placed the films in a vacuum, to simulate the conditions found in space, and then blasted them with low energy electrons. Their work, which was published in the Journal of Chemical Physics, found some interesting results:

“We see the formation of things like ethanol, for example, which is a much more complex molecule than the simple methane and oxygen in the film,” explains Michael. “Clearly, ethanol is not a building block of life, but you can imagine that over astronomical timescales, you could make molecules like amino acids”.

Given that these low energy electrons can make simple molecules combine to form complex ones, it is possible that by adding more molecular “ingredients” to the original film, amino acids could be produced. If this happened on comets in our solar system billions of years ago, that could explain the origin of life on Earth.

“In the early days of the Earth, when there was heavy bombardment by meteorites, it’s possible that these building blocks of life arrived on Earth through meteorite impacts.”

And if life’s building blocks did form in space, who knows? Earth might not be the only planet they landed on...

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