Space Science Division, NASA Ames Research Center, Moffett Field, California, USA.
Department of Earth and Space Sciences, University of Washington, Seattle, Washington, USA.
Astrobiology. 2024 Sep;24(9):881-891. doi: 10.1089/ast.2023.0128.
Big impacts on the early Earth would have created highly reducing atmospheres that generated molecules needed for the origin of life, such as nitriles. However, such impactors could have been followed by collisions that were sufficiently big to vaporize the ocean and destroy any pre-existing life. Thus, a post-impact-reducing atmosphere that gives rise to life needs to be followed by a lack of subsequent sterilizing impacts for life to persist. We assume that prebiotic chemistry required a post-impact-reducing atmosphere. Then, using statistics for the impact history on Earth and the minimum impact mass needed to generate post-impact highly reducing atmospheres, we show that the median timing of impact-driven biopoiesis is favored early in the Hadean, ∼4.35 Ga. However, uncertainties are large because impact bombardment is stochastic, and so biopoiesis could have occurred between 4.45 and 3.9 Ga within 95% uncertainty. In an optimistic scenario for biopoiesis from post-impact-reducing atmospheres, we find that the origin of life is favorable in ∼90% of stochastic impact realizations. In our most pessimistic case, biopoiesis is still fairly likely (∼20% chance). This potentially bodes well for life on rocky exoplanets that have experienced an early episode of impact bombardment given how planets form.
大撞击会在早期地球上产生高度还原的大气，从而产生生命起源所需的分子，如腈类。然而，随后的撞击可能足够大，足以蒸发海洋并摧毁任何先前存在的生命。因此，为了生命的持续存在，引发生命的撞击后还原大气需要随后缺乏杀菌撞击。我们假设前生物化学需要撞击后还原大气。然后，我们使用地球撞击历史的统计数据和产生撞击后高度还原大气所需的最小撞击质量，表明撞击驱动生物发生的中位数时间有利于早期的冥古宙，约 43.5 亿年前。然而，由于撞击是随机的，因此不确定性很大，因此生物发生可能发生在 44.5 亿到 39 亿年前之间，置信度为 95%。在一个乐观的情况下，即从撞击后还原大气中产生生物，我们发现生命起源的可能性在 90%的随机撞击实现中是有利的。在我们最悲观的情况下，生物发生的可能性仍然相当高（约 20%的机会）。这对于经历过早期撞击轰炸的岩石系外行星上的生命来说是个好兆头，因为行星是如何形成的。
