Early Earth did not need to protect itself against the cold, as it was actually much warmer back then. During the Archean and Proterozoic Eons, which spanned from about 3.8 billion years ago to 541 million years ago, Earth experienced extremely high temperatures known as the "hot Earth" or "hot-house" phases. At that time, carbon dioxide and methane levels were elevated in the atmosphere and acted as greenhouse gases, creating a warm and humid environment suitable for the development of early life forms. It was only later on, during periods like the Cryogenian period and the ice ages, that Earth experienced major cooling episodes and glaciations.