Author: Graham Shields, Professor of Geology, UCL

More than 700 million years ago, the Earth was plunged into a state that geologists call “snowball Earth”, when our planet was entirely encased in ice. This happened when the polar ice caps expanded so far that they joined up around the equator. Several lines of evidence show that the snowball Earth happened, but we have previously lacked rocks showing the landscape entering this big freeze. We may now have found this on tiny islands known as the Garvellachs, off the west coast of Scotland. Sedimentary rocks are in layers that can record major events on Earth. For example, there’s…