Space

Lots of clues suggest there’s life beyond Earth, but probably nothing as complex as us.

Could we be alone in the Universe?

IN ASTROBIOLOGY, experts investigate the origins and evolution of life on Earth – and beyond. It’s not strictly focused on the search for extraterrestrial life, but that’s one exciting aspect.

Astrobiologists are hopeful of success.Their optimism springs from the fact that living organisms are found in every niche on Earth. And water – the working fluid of all life on our planet – seems abundant in space, as are suggestive carbon-based compounds. Also abundant are planets – perhaps up to 2 x 1023 of them in the Universe.

The conclusion is that extraterrestrial life might be everywhere, and, with our sights set on Mars and some of the promising moons of Jupiter and Saturn, it may not be long before we find it. But that’s simple life – single-celled organisms, or microbes.

The evolution of these into complex life forms might be much rarer. We know the first microbial life appeared on the Earth some 4 billion years ago, but the first complex organism took at least another 2 billion years to emerge. And it did so once only. How do we know? Because all complex life on Earth – eukaryotes – can be traced genetically to a unique progenitor, known as LUCA (Last Universal Common Ancestor). So far, we’ve found no sign of an evolutionary false start that could hint at a second genesis of eukaryotes on Earth.

A few scientists point to basic thermodynamics as to why, because eukaryotes are vastly more energy-hungry than their single-celled ancestors.Thus, there is pessimism about the development of any multicellular organisms beyond Earth – let alone higher life forms and ETs.

A recent Oxford University study suggests that despite the vast number of planets in the known Universe, they are unlikely to host any other civilisations.

The idea of a huge, complex Universe with just one fragile species able to contemplate it is strangely disturbing.What is it for? Does it suggest that somehow we don’t belong here…?

One theory about the origin of eukaryotic cells – like those in multicellular animals – is that several unicellular prokaryotic cells combined, as this illustration depicts.