Unfortunately, the overwhelming majority of the oldest rocks on Earth have been destroyed or altered by geological processes such as tectonic shift. Consequently, the geological record is extremely poor for the first billion years of Earth's 4.5 billion year history,18 and so all we know is that life arose during a one-billion year window — an enormous span of time, roughly twice as long as complex animals have existed.
The limited geological evidence also means there is little information about conditions on the early Earth. The temperature range, the presence or absence of exposed land, and the chemical makeup of the oceans and atmosphere, as well as the elemental composition are all central issues for understanding which scenarios of the origin of life are plausible.1920 For instance, some scenarios rely on the existence of ponds or pools on land, but if the oceans were too deep there cannot have been any land.21 These questions are bound up with fundamental problems in geology, notably the origin of modern plate tectonics.22
Improvements in our understanding of the geological record will continue to narrow down when and how life may have formed. A key challenge for palaeontologists and geologists is to narrow the time window for the origin of life, either by finding hard evidence of earlier life, by building on innovative synthetic biology and evolutionary systems biology tools to reconstruct ancient life,23 or by demonstrating that conditions before a certain point were unremittingly hostile.24
