US scientists have come up with new evidence that the key ingredients for life were brought to our planet by comets, billions of years ago.
There had been questions over whether amino acids and other elements of life could have survived a cometary impact.
"Our research shows that the building blocks of life could, indeed, have remained intact despite the tremendous shock wave and other violent conditions in a comet impact," says Jennifer Blank, who led the research team.
"Comets really would have been the ideal packages for delivering ingredients for the chemical evolution thought to have resulted in life. We like the comet delivery scenario because it includes all of the ingredients for life — amino acids, water and energy."
Evidence suggests that life on Earth began at the end of a period 3.8 billion years ago called the late heavy bombardment that involved multiple strikes from both comets and asteroids. Before that, Earth was too hot forliving things to survive.
The earliest known signs of life date from 3.5 billion years ago.
Blank, together with colleagues at the Bay Area Environmental Research Institute and NASA/Ames Research Center, examinedwhether amino acids could remain intact after a comet's descent through Earth's atmosphere.
They used gas guns to simulate the enormous temperatures and powerful shock waves that amino acids in comets would experience on upon entering Earth's atmosphere, firing the gas at capsules filled with amino acids, water and other materials.
And, they found, the amino acids didn't break down - indeed, they began forming the peptide bonds that link them together into proteins. The pressure from the impact of the crash apparently offset the intense heat and also supplied the energy needed to create the peptides, says Blank.
She suggests that there may well have been multiple deliveries of amino acids over the millenia from comets, asteroids and meteorites.