ABSTRACT
The Earth's climate has not always been as it is today. There have been times in the geological past when the global climate was warmer or considerably colder than at present. The geographic and temporal distribution of organisms, preserved as fossils, and the particular chemical signatures and sediment types available for study, show that the Earth's climate has fluctuated over geological time. As an example, 4.5-3.5 miUion years ago, parts of eastern Antarctica were a lot warmer. During the Tertiary Period of Earth history, from about 65 million years ago (65 Ma ), but prior to 1.64 Ma, boreal forests were growing in the Canadian High Arctic as far north as 7S"N, now preserved as fossil forests (Plate 2.1). Although it is now known that there have been substantially different climates in the past, the exact causes of such variations remain unclear.
