Geology 37, 1011–1014 (2009)

A huge meteorite or comet that smashed into North America 1.85 billion years ago was responsible for the abrupt end of certain iron deposits in the rocks around Lake Superior, say John Slack and William Cannon from the US Geological Survey in Reston, Virginia. They propose that the collision, dubbed the Sudbury impact, caused dramatic changes in the oxygen levels of the deep oceans.

The impact probably caused a giant tsunami and other mixing processes that brought small amounts of dissolved oxygen to the previously oxygen-free deep ocean. Oxygen would have lowered the solubility of iron from hydrothermal vents, hindering its journey to the continental margin, an area where ocean crust and continental crust meet. This stopped the deposition of banded iron formations in the rocks of this region, say the authors.