(EN) Orgel Le, The origin of life: a review of facts and speculations, in Trends in Biochemical Sciences, vol. 23, n. 12, 1998, pp. 491-5, PMID 9868373. URL consultato il 28 marzo 2015.
«Life, therefore, originated on or was transported to the earth at some point within a window of a few hundred million years that opened about four billion years ago.»