Earth was a snowball
Earth experienced 5 large ice ages. During this time, a hefty layer of ice smothered our planet.
It was unimaginably frigid at this time where temperatures dropped to 10°C lower than it is today.
Ice ages happen for several reasons. In the eyes of Milankovitch, Earth is prone to ice ages because of how its cyclical movements affects climate.
At least, this is reasonable to assume for the last ice age 10,000 years ago. Atmospheric chemistry, solar output and ocean currents can trigger ice ages.