The Northern Hemisphere ice sheet is ephemeral…
318861 BCE to 298126 BCE
The Northern Hemisphere ice sheet is ephemeral before the onset of extensive glaciation over Greenland that occurs in the late Pliocene around three hundred thousand years ago.
The formation of an Arctic ice cap is signaled by an abrupt shift in oxygen isotope ratios and ice-rafted cobbles in the North Atlantic and North Pacific ocean beds.
Mid-latitude glaciation is probably underway before the end of the epoch.
The global cooling that occurs during the Pliocene may have spurred on the disappearance of forests and the spread of grasslands and savannas.