This paper is an overview of the more popular theories for the occurrence of ice ages. No consensus has been reached to definitely explain the causes for ice ages, but four theories are detailed here. Reduction of CO2, volcanoes, continental changes, and earth's orbital changes are theories that will be discussed. There are many more theories that could be described, however many of these theories lacked support. The ideas discussed here are all backed by some degree of scientific evidence and thus deserve consideration. .
INTRODUCTION.
Since man's initial curiosity about the history of his earth, much has been discovered about the way the earth moves and changes, including its climate. Scientists have found geologic evidence of at least five ice ages. The first seemed to occur more than two billion years ago and the most recent peeked just 18,000 years ago (Hughes 1993, pg. 11). However, there is one mystery that has seemed to elude scientists from all over the world for quite some time. This mystery is the cause of the several eras of ice that have appeared many times throughout earth's history. There have been numerous theories formulated to explain these "glacial epochs" (Hughes 1993, pg.13), but none have been proven. The most popular theories include a reduction of CO2 in the atmosphere, volcanic eruptions, changes in continental positions and continental blocks, and changes in the earth's orbit (Anon, 2001).
REDUCTION OF CO2.
Several scientists will agree that a reduction in CO2 may be one factor that leads to the ice ages. Because carbon dioxide "traps sunlight close to the earth, less carbon dioxide in the atmosphere means colder weather" (Watson, 1997). Over the past 160,000 years, including two ice ages, global temperatures have fluctuated in sync with carbon dioxide levels (Hughes 1993, pg. 17).
Still, that does not explain why the carbon dioxide levels fell. Some believe that the drop is associated with "weathering - a process [where] carbon dioxide washed out of the atmosphere by constant rain [is] fixed in carbonate rocks" (Hughes 1993, pg.
