The Snowball Earth hypothesis explains glacial deposits in the Huronian supergroup of Canada. The palaeomagnetic evidence, which suggests ice sheets at low latitudes, is contested. The glacial sediments of the Makganyene formation of South Africa are slightly younger than the Huronian glacial deposits (~2.25 billion years old) and were deposited at tropical latitudes. Perhaps the rise of free oxygen that occurred during this part of the Paleoproterozoic removed methane in the atmosphere through oxidation. As the Sun was notably weaker at the time, the Earth's climate may have relied on methane, a powerful greenhouse gas, to maintain surface temperatures above freezing. In the absence of this methane greenhouse, temperatures plunged and a snowball event could have occurred.