2020 events

Sun 11:30-12:30
Sunset Room

Are we alone in the Galaxy? Probably no little green men, but lots of little microbes

David Moriarty


Astronomers are seeking Earth-like planets and are being asked whether there could be life on them; however, they alone cannot answer that question. It requires a multidisciplinary input that includes chemistry, geology, geochemistry, biochemistry, and microbial ecology.

If life evolved elsewhere, organisms would depend upon the same laws of physics and chemistry that apply on Earth and therefore they would be similar. Recent research into the origin of life on Earth shows that it is a planetary process and thus microbial life would be expected on planets formed with similar processes elsewhere in the Galaxy.

All life is organic, based on the chemistry of carbon and its interactions with oxygen, nitrogen, hydrogen, sulphur, and phosphorus. The energy generating processes that sustain the life of all organisms depend on water and the transition metals, especially iron, copper, and nickel. Their role points to the geochemical origins of life on Earth soon after it cooled and oceans had formed. Microbes were the only organisms on Earth for the first 3 billion years. The original microbes obtained energy for life from hydrogen and used it to reduce carbon dioxide and nitrogen to synthesise organic compounds. Oxygen was poisonous to them.

There is a huge difference between microbes and complex, multicellular organisms. Complex organisms have a much greater demand for energy than can be supplied by anaerobic hydrogen oxidation. They require the much larger amounts of energy released when electrons are transferred to oxygen. Oxygen was not present in sufficient concentration until about 2 billion years ago for them to evolve, and not at a high enough concentration for multicellular organisms to evolve until about 600 million years ago.