Free Astronomy Magazine January-February 2019

ASTROBIOLOGY 39 nets, estbed JANUARY-FEBRUARY 2019 A bout the diffusion of life in the universe, we have only one certainty: it is present on our planet. Any region of the Earth, even the most inhospitable, pullulates with life. Chemistry, biology and paleontology have discovered a great deal about current and past forms of life on our planet. However, in spite of great scientific and technological progress in the last decades, we still do not know how and when the first living organisms appeared. Since the pioneering laboratory experiments of Stanley Miller and Harold Urey in the 1950s, nothing has substan- tially changed: biochemists know how to produce amino acids and proteins necessary for life; they know how to do it by simulating the likely terrestrial environment bil- lions of years ago, but no scientist has so far managed to take the decisive step of transforming complex or- ganic molecules into self-replicating living organisms. This apparent inability to generate life here on Earth beginning from its fundamental building blocks has re- peatedly reinvigorated the panspermia hypothesis, ac- cording to which life has spread in the cosmos through “seeds” transported by interstellar dust, meteoroids and comets of various sizes. Perhaps the young Earth did not have the necessary requisites to generate life,