Other Worlds and the Origin of Life

  Microbial Fossil

Astrobiology or exobiology is a relatively new field which draws upon many other sciences such as astronomy, biology and geology. Scientists working in this field ask searching questions such as what is life, how did it arise on Earth and will it be found on other planets? NASA has a dedicated Institute of Astrobiology and many universities offer degree programmes in the subject. Leicester University is unusual in that it offers an interdisciplinary degree and we were fortunate to have as our speaker Dr Derek Raine the course director for i-Science. He gave us an overview of how scientists are trying to remove the mystery surrounding the origin of life and its extent.

At present there is only one planet that definitely has life - the Earth. Using this sample of one, astrobiologists study the emergence of life on our blue planet in order to predict whether it is likely elsewhere. It is thought that life emerged on Earth around 3.5 billion years ago, which is only 300 million years after the period when cometary impacts were commonplace. Although this seems a long time in terms of a human lifespan this is a mere blink of the eye in terms of the evolution of life on Earth.

Back in 1953 at Chicago University a pair of scientists, Stanley Miller and Harold Urey, conducted an experiment to see what the effect of lightning would have on the chemical soup that was present on the early Earth. After a week of zapping a chemical mixture with electricity some of the carbon had changed into organic compounds and amino acids. However, this was still a long way from the complex proteins and physical structures that we know of as life.

How these simple chemical molecules could make the leap into highly organised cells has been a great stumbling block. There are two competing theories as to how this could happen. One is known as "RNA world" where RNA structures catalyse their own reactions, and in this way can reproduce. (RNA is similar to DNA but only has a single polymer strand and differs slightly in composition). The other theory is known as "cells first" whereby physical processes produce cell- like structures with membranes.

What is agreed upon is that it was evolutionary pressures that drove the increase in complexity, as it was impossible for pure chance to be responsible for the emergence and development of complex lifeforms.

If life is `out thereī and we are lucky enough to find it, even in a primitive form, it will help to fill in some of the gaps in our scientific knowledge. The three nearest candidates are Mars, Europa (Jupiterīs moon) and Europa (Saturnīs moon) but it will not be long before Earth-sized planets will be having their atmospheres examined. Perhaps the real question should be - are we ready psychologically to find out?