Where did life come from?

How did we get here, how did life first take hold on planet Earth and spark the billions of years of evolution that led to human beings existing? Answering that question could reveal whether life here was just a fluke, or the residue of something much bigger spread across the cosmos. Some suggest the building blocks of life were present here from the start, molecules that came together by fateful accident in some kind of primordial soup producing the most primitive life. Then the process of natural selection took its course and billions of years later, viola, bi-peds like us were walking around.

Others suggest the key components needed for life were deposited here by meteorites or comets from outer space. The Panspermia theory holds that tiny microbes hitched rides on meteorites or comets, interstellar astronauts that were deposited here when rocks hit the Earth’s surface. A basic version of that theory has just been given more scientific credence. Scientists reported last week that they had discovered the last two of the five informational units of DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) in samples of meteorites.

DNA and RNA contain the genetic instructions that underpin every life form on Earth. Five socalled nucleobases, types of organic compounds, contain the informational components that make up DNA and RNA, which acts as a messenger that tells your cells what to do.

Scientists had previously found traces of three of the nucleobases in meteorites. The final two, cytosine and thymine, have only now been discovered using, more sensitive techniques on samples taken from three meteorites, including one that hit the Earth near the town of Murchison in Victoria, Australia, in 1969.

The presence of these five crucial nucleobases in space rock suggests some crucial ingredients could have come from elsewhere in the universe. What happened when those various organic compounds came together around 4 billion years ago is the subject of intense scientific debate.

University of Auckland biophysicist Dr Peter Wills and colleagues have just received a $2.2 million grant from the US-based Alfred P. Sloan Foundation, to undertake a bioinformatics project to try to find out. The RNA world theory holds that life began with an RNA molecule that could copy itself, and the better-known DNA emerged later.

Wills’ team is suggesting that RNA probably didn’t selfreplicate, but that it evolved with peptides – strings of amino acid – to develop the genetic code underpinning life.

Our origin story is still to be fully understood and written. But it will eventually make for one of the most remarkable chapters in the history of life itself.

DNA and RNA contain the genetic instructions that underpin every life form on Earth.