The protein survives in the extreme environments of high acidity and temperature expected on early Earth and, intriguingly, also Mars.

Spanish and US scientists reported their study in the journal Structure.

Gene sequences in a protein called thioredoxin, taken from a wide variety of modern organisms, were analysed and placed in an evolutionary context - locating them on a molecular-scale tree of life - to chart their progression from their primordial forms.

First, computer analysis was used to determine how modern genetic sequences developed from original codes, so the ancient DNA sequences in the protein from as far back as four billion years ago could be determined.