The building blocks of DNA have been found in samples returned to Earth from an asteroid, suggesting life rained down from space and could have formed elsewhere.
In 2016, Nasa sent its Osiris-Rex mission to drill down into the asteroid Bennu, with the cargo returning to Earth in 2023.
The first analysis shows that the four nucleotide bases of DNA – adenine, guanine, cytosine and thymine – which form the rungs of the double helix, were all present. 
Every living thing on Earth contains DNA, which stores the genetic information needed to build and maintain an organism.
It is the first time that all four nucleotide bases have been discovered together on an asteroid, and the samples were also found to contain 14 of the 20 amino acids that life on Earth uses to make proteins.
Nasa said the findings not only suggest that space rocks sparked life on Earth, but that the conditions for life were widespread across the early solar system.
Nicky Fox, the associate administrator for the Nasa Science Mission Directorate, said: “Bennu contains many precursor building blocks of life along with the evidence it comes from an ancient wet world.
