A change in the temperature. Under anaerobic conditions, soluble organic phosphate compounds are produced as a result of decomposition. Ferrous and manganous phosphates are soluble. Under anaerobic conditions organisms excrete soluble inorganic phosphate. The end of the Tertiary Period was marked by a progressive cooling of the earth's atmosphere.
Eccentricity is the angle of tilt of the earth's axis.
At the end of the Tertiary Period coniferous forests were widespread on the islands of the Canadian Archipelago. Snow and ice lead to increased reflectance of incoming radiation. Beringia was unglaciated in the last glaciation. There was only one glaciation in the Northern Hemisphere during the Quaternary Period. The climate has become progressively warmer in the present interglacial.