Study finds comets unlikely to have delivered life's chemical ingredients to early Earth

Mixed · 2A study published in the journal Scientific Reports concludes that comets striking the early Earth would very probably not have delivered the organic ingredients of life intact. 1 2 Mixed · 2The work was led by Dr Richard Anslow of the University of Cambridge's Institute of Astronomy, and used computer simulations centred on hydrogen cyanide (HCN), a compound of hydrogen, carbon and nitrogen that is important in prebiotic chemistry. 1 2 Mixed · 2The modelling found that even if all cometary material had been deposited into Earth's oceans at once, the HCN concentration would reach only about 0.75 micromoles per litre, roughly 13,000 times below the level needed for the key chemical reactions examined. 1 2

Mixed · 2The simulations estimated that comets delivered about 2.63 quadrillion tonnes of material over 500 million years, equal to about 0.19 per cent of the mass of the oceans, and that more than 100,000 comets wider than 100 metres hit the early Earth. 1 2 Centre · 1Gulf News, citing CNN, reports that 54 per cent of the simulations produced no successful delivery events and only a small minority produced as many as three. 2 Right · 1Anslow said the idea is "kind of a romantic idea, but our results suggest it's highly unlikely"; GB News quotes him saying success would be "a one-in-a-million occurrence" needing the right impact speed and angle plus favourable conditions afterwards, and that a comet origin cannot be ruled out for certain. 1

Mixed · 2The authors point to alternatives: asteroids, which hit Earth more often and at lower speeds and may have produced the molecules through impact heat, or chemistry in Earth's own atmosphere, water and minerals without extraterrestrial input. 1 2 Centre · 1Gulf News adds that samples from the asteroids Bennu and Ryugu have shown a rich range of organic molecules, including amino acids. 2 Mixed · 2The researchers say Mars, being smaller with a thinner atmosphere, may have been a marginally better recipient of intact cometary material, though Anslow said this does not mean life began there and that it may have happened on neither planet. 1 2

Right · 1The authors suggest the results could help target the search for life beyond the Solar System, for example systems with tightly packed planets where comets could slow down by bouncing between worlds. 1 Centre · 1Not all researchers treat the comet idea as finished: Queenie Chan of Royal Holloway, University of London, told CNN that HCN might have reacted into other biologically important compounds before entering the atmosphere, which could be likelier to survive an impact. 2 Right · 1The study was funded by the Royal Society, the Leverhulme Centre for Life in the Universe and the Science and Technology Facilities Council. 1