As we have seen in The earth’s thermostat chemical weathering is an important mechanism in regulating CO₂ concentrations and thus the climate on a long term range. The rate of chemical weathering on earth depends on the type of terrain and it is elevated by a factor of 50 in high mountains when compared to the rate in Basins (Ruddiman, 2001, p. 167).

Thus, the uplift of the Tibetan Plateau and the Himalaya is thought to have increased chemical weathering on a global scale and to have caused a consequent drop in atmospheric concentration of the important greenhouse gas CO₂. This long-term decrease is probably responsible for the cooling trend over the last 50 million years. Antarctica that had been ice-free for millions of years started to build up its ice cap between 34 and 40 million years ago.

Around 2.7 million years ago, it had become cold enough to allow for perennial ice to persist in the Northern Hemisphere and the huge ice cap on Greenland came into existence (Haug et al., 2005). This boundary marked the start of a new geologic era, the so called Quaternary. It was also the time when the genus homo appeared on earth.

References

Ruddiman, W. F., 2001. Earth’s climate: Past and Future. W. H. Freeman and Company, New York.

Haug, G. H., Ganopolski, A., Sigman, D. M., Rosell-Mele, A., Swann, G. E. A., Tiedemann, R., Jaccard, S. L., Bollmann, J., Maslin, M. A., Leng, M. J., and Eglinton, G., 2005. North Pacific seasonality and the glaciation of North America 2.7 million years ago. Nature, 433(7028), 821–825.