Scientists have raised fresh doubts on a popular theory that suggests some of the building blocks of life on Earth were brought here by comets, after they discovered that such cosmic objects could have wiped them out when they crashed into the planet billions of years ago.
For years, scientists have speculated that comets could have delivered organic compounds to the early Earth that contributed to the evolution of life.
But a new study by researchers at the University of Cambridge suggests that the theory has a major problem: the comets may have been travelling too fast for those chemicals to survive the impact.
The findings, published in Scientific Reports, are based on 100,000 computer simulations examining what happens when comets collide with a planet.
Researchers focused on compounds such as hydrogen cyanide, which can play an important role in the chemical reactions that produce amino acids, the building blocks of proteins.
Their calculations suggest that the extreme heat and pressure generated during most comet impacts would have destroyed these fragile compounds before they could contribute to the emergence of life.
Lead researcher Richard Anslow said the possibility of comets delivering the necessary ingredients could not be ruled out entirely, although it would have required unusually favourable circumstances.
The findings also raise questions about whether Mars might have been better placed to receive such chemicals, given differences in the conditions under which comets strike the two planets.
Scientists are now considering whether asteroids played a bigger role in delivering organic material to Earth, or whether the ingredients for life formed here through natural chemical processes.
The study does not explain how life began. It does, however, cast doubt on one proposed route by which some of its essential ingredients may have arrived.
