There have been long periods of cooling in Earth’s history. Temperatures had already fallen for more than 10 million years before the last ice age began about 2.5 million years ago. At that time, the northern hemisphere was covered with massive ice masses and glaciers. A geoscientific paradigm, widespread for over 20 years, explains this cooling with the formation of the large mountain ranges such as the Andes, the Himalayas and the Alps. As a result, more rock weathering has taken place, the paradigm suggests. This in turn removed more carbon dioxide (CO2) from the atmosphere, so that the greenhouse effect decreased and the atmosphere cooled. This and other processes eventually led to the ice Age.
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Source: Phys.org