In this lecture Dr Zita Martins was charged with answering two questions: “How did life start on Earth?” and “Are we alone in the universe?”.
She failed to answer either question.
But that maybe a little harsh. Zita is a young Portuguese professor with a very impressive sounding CV. She’s a multilingual, multi-disciplinary astrobiologist.
Her aim is to push forward our understanding of how life began on Earth; more specifically, whether the ingredients necessary prior to the formation of the most basic lifeforms were present on the Earth or came from somewhere else.
She gave a brief overview of previous work in the area, and rubbished the Miller-Urey experiment as the conditions they used to generate their amino acids were not at all like the conditions on the Earth when we believe life was formed; she drew attention to the most likely energy source being UV light whereas theirs was simulated lightning.
She then described that the earth was heavily bombarded by comets and meteorites during the period between 4.6 – 2.8 billion years ago, and life was formed around 3.6 billion years ago (the oldest fossils are from that time which are made up of algae and cyanobacteria).
And so this is why she is studying the contents of meteorites for two key types of organic compounds: amino acids (the building blocks of proteins and enzymes) and nucleobases (the components of DNA and RNA). Building blocks which are otherwise very rare in terrestrial sources.
She said we know that all the key compounds required for terrestrial biochemistry have been identified as extraterrestrial components from meteorites she has studied. Interestingly we only need about 20 amino acids for terrestrial life, but she described meteorites that contained 80.
It’s worth defining organic compounds as those which contain carbon, not those which contain any form of life. During questions, she said that the likelihood of any kind of living organism arriving on a meteorite is near zero given the conditions in space. So it’s most likely that the organic compounds arrived by meteorite, and what actually transformed them into life probably happened on earth.
As for the second question, following this theory of how it happened here on earth, she said that there had been a lot of meteorites hitting Mars but there’s too much we don’t know before anything more can be said – we are reduced to looking for evidence of water there until our technology gets better.
Martins had an impressive scientific attitude: she was quite happy to be proven wrong in the assumptions that are the basis of her approach and didn’t seem to be emotionally attached to them when they were challenged. She easily admitted that the discoveries and theories made so far may be trumped by new ones.
She conceded that we haven’t got the faintest clue how these building blocks became living, reproducing entities. Claims you see in the papers from time to time that say otherwise are not true thus far.
The biggest idea I took away was that this is very much a nascent science and we know very little in this area (an area in which she is at the cutting edge). Martins said we will probably never know exactly how life was started here on Earth.