The evidence is piling up that the building blocks of life could have been brought to Earth by comets, after emerging in the dust of interplanetary space.
Chemists from the University of California, Berkeley, and the University of Hawaii have shown that conditions in space could lead to the emergence of complex dipeptides - linked pairs of amino acids - that are fundamental to all living things.
Scientists have, on many occasions, discovered basic organic molecules such as amino acids in meteorites that have fallen to Earth. Back in 2010, for example, a meteorite that fell in Australia in 1969 was revealed to contain 'several million' different organic chemicals.
However, what's been missing until now are the more complex molecular structures that underlie our planet's biology - leading scientists to assume that the really complicated chemistry of life must have been kick-started in Earth's early oceans, rather than space.
But the analysis of the substances created in the team's experiments shows nine different amino acids and at least two dipeptides - 'capable of catalyzing biological evolution on Earth', says the team.
In an ultra-high vacuum chamber chilled to 10 degrees above absolute zero, the team simulated an icy snowball in space, containing carbon dioxide, ammonia and various hydrocarbons such as methane, ethane and propane.
When zapped with high-energy electrons to simulate the cosmic rays in space, the chemicals reacted to form complex, organic compounds - including, most notably, dipeptides, essential to life.
"It is fascinating to consider that the most basic biochemical building blocks that led to life on Earth may well have had an extraterrestrial origin," says UC Berkeley chemist Richard Mathies.