Scientists have found that 4.02 billion year old silica-rich felsic rocks from the Acasta River, Canada—the oldest rock formation known on Earth—probably formed at high temperatures and at a surprisingly shallow depth of the planet’s nascent crust. The high temperatures needed to melt the shallow crust were likely caused by a meteorite bombardment around half a billion years after the planet formed. This melted the iron-rich crust and formed the granites we see today. These results are presented for the first time at the Goldschmidt conference in Boston tomorrow (14 August), following publication in the peer-reviewed journal Nature Geoscience.