Free Astronomy Magazine January-February 2021

28 JANUARY-FEBRUARY 2021 ASTRO PUBLISHING 3.5 billion years ago, at the end of the Late Heavy Bombardment, a pe- riod that upset the still fragile Earth’s crust with relatively frequent gigantic impacts (about one per cen- tury) that were capable of both keeping large continental areas liq- uefied and also evaporating the pri- mordial seas, leaving immense scars that would soon be erased by new and gradually smaller events. Surely, this was not the most favorable sce- A thermal ecosystem originating from the Chicxulub event S cientists do not yet know how life appeared on Earth, nor do they know precisely in which environments it first appeared. Since we learned, from studies in the 1990s, that the first organisms were likely thermophiles, it is plausible to conclude that life originated in very hot environments, such as hydro- thermal systems linked to underwa- ter volcanic activity. Those first or- ganisms appeared between 3.8 and by Michele Ferrara revised by Damian G. Allis NASA Solar System Ambassador I n the background, a reconstruction of the Chicxulub crater, as it might have appeared in the years following the impact of the asteroid that originated it. [Detlev Van Ravenswaay/Science Source]