glaciation

That the habitability of our planet was severely endangered by the significant rise in oxygen levels and reduction in methane due to oxygen-producing bacteria combined with the low luminosity of the Sun in the Proterozoic era (2500– 542 million years ago) is suggested by geological evidence for severe global glaciations in this epoch.

Deposits of the Caribou Hills glaciation only locally retain a distinct hummocky morainal form, with filled kettle depressions and subdued knobs. Along the mountain fronts the marginal deposits of this glaciation reach an average altitude of slightly more than 3,000 feet.

For cave glaciation to occur it is necessary that the air temperature outside the caves be negative either for all or part of a year; such conditions exist in many regions of the world.