clock-resetting by impact tagged posts

This highly shocked zircon, from the Vredefort Dome in South Africa, shows thin, red bands that are a hallmark of meteorite impact. Photo: Aaron Cavosie

A study of zircons from a gigantic meteorite impact in South Africa casts doubt on the methods used to date lunar impacts. Durable crystals zircons are used to date some of the earliest and most dramatic cataclysms of the solar system. One is the super-duty collision that ejected material from Earth to form the moon roughly 50 million years after Earth formed. Another is the late heavy bombardment, a wave of impacts that may have created hellish surface conditions on the young Earth, about 4 billion years ago.

Both events are widely accepted but unproven, so geoscientists are eager for more details and better dates...