http://www.sciencemag.org/news/2019/08/shock-and-thaw-earth-s-oldest-asteroid-impact-may-have-helped-lift-planet-out-deep

Oxygen from ancient life may have led to Snowball Earth (artist’s concept). Did an impact help it thaw?

BARCELONA, SPAIN—Barlangi Rock, an ancient hill in the outback of Western Australia, is dimpled by the quarries of Aboriginal people who chiseled its fine-grained rocks into sharp tools. Now, geologists have added a much deeper layer of history to those rocks by showing they were forged 2.229 billion years ago, when an asteroid crashed into our planet. The finding makes Yarrabubba crater, the 70-kilometer-wide scar left by the collision, Earth’s oldest.