Brownlee said the result is exciting because it represents a second, very large source of life-giving material. He estimated that there are as many as a trillion comets in and around the solar system, many of them in the chilly Kuiper Belt beyond Pluto, or in the Oort Cloud even farther out.

“There has been a huge question of where the prebiotic compounds came from on Earth,” Brownlee said. “Did they come from space? Or were they made here? Or maybe they came from both places.”

Just having the right materials is no guarantee that life will begin, of course, any more than leaving a hammer, nails and planks lying around will cause a barn to rise. Brownlee pointed out that many of the 30,000 or so meteorites that have been found on Earth bear traces of organic compounds, and there also is evidence that they were once warm and wet, all necessary conditions for life. Yet none of the meteorites has shown any evidence of life forms.

“They are all failed places where life could have arisen,” Brownlee said.