Geology (2013)

Between roughly 650 and 635 million years ago, much (if not all) of the Earth was covered by ice and snow. Dating of rock units that formed following the end of the glaciation suggests that the termination of this Marinoan Snowball Earth event was synchronous around the world.

Clive Calver of Mineral Resources Tasmania and colleagues measured the uranium and lead contents of volcanic zircons collected from the Cottons Breccia unit, part of the Marinoan-aged rock formation located on Kings Island, Tasmania. The unit formed at low latitudes, and consists of glacial and marine rocks that were deposited during and immediately after the Marinoan glaciation. The team identified volcanic ash within the younger layers, which gave a U-Pb age of about 636 million years.

This timing for the Marinoan meltdown is consistent with ages for the end of the Marinoan glaciation obtained from rocks located in Namibia and South China, indicating that the end of this Snowball Earth occurred synchronously around the globe, at least on a million-year timescale.