After the bombardment eases
A three-dimensional numerical model of Hadean crust, published on 22 September in Nature Communications, places a proposed RNA World at about 4.33 billion years ago. Frequent global sterilization, from hot ejecta, rock vapour and a raised geothermal gradient, lasts until about 4.4 billion years ago. The model then finds linked zones of thermal stability for nucleotides, peptides and lipids, associated with energy-rich hydrothermal oases.[1]
Estimates for when life emerged still run from about 3.8 billion years ago to the Hadean, at or before 4.0 to 4.5 billion years ago. The authors describe 4.33 billion years ago as an interval that lines up with estimates for the last universal common ancestor (LUCA) population. The quantity they tracked is the thermal stability of building blocks. The same mild niches can sit empty if a copying chemistry never takes hold.[1]
The gap left for tonight
The 4.33 billion years ago mark is an output of a model run under late bombardment. If a later peer-reviewed chronology moves the end of global sterilization far from 4.4 billion years ago, the 4.33 billion years ago center moves with it. The sign to watch is publication of that chronology.[1]
The 4.33 billion years ago mark is this model's calm interval for fragile chemistry. The beginning of life stays unmeasured. The part to keep in view tonight is that gap: a time when the surface has room for a chemistry that persists.[1]