The 'Landforms of New York City' investigation introduced the concept of the Glacial Theory. This theory declares that from about 2 million years ago until 15 thousand years ago, large portions of the land surface of the earth were covered by flowing ice.

'The Drowning of New York', the final investigation of the term, will consider the likelihood of New York City being inundated in the near future. Arguments will be made that depend in part upon data shown in graphs displaying the temperature of the earth's atmosphere from today all the way back to 800 million years ago.

In both these investigations, an implicit assumption is that geologists have a reliable way of determining the earth's history - that somehow they can travel back in time. Moreover, for 'The Drowning of New York', it will be suggested that conclusions drawn about past atmospheric temperature may be used to make judgments about atmospheric temperature in the future.


But what if the geologists are wrong? In the skeptical spirit which we have developed, surely we must ask 'what is the basis upon which geologists have come to believe they can know the past?' And 'what is it that makes geologists so confident of their conclusions about the past that, based upon those conclusions, they are willing to make predictions about the future?'


Time is sometimes called 'the fourth dimension'. It is a dimension in which geologists strive to feel at home. Geologists have as a major goal the working out of the earth's history. Is this goal realistic? Finding an answer to that question will be the focus of this investigation.


An inquiry into geologists' beliefs must examine what geologists have observed, the hypotheses they construct to explain those observations, and the assumptions that underlie the tests to which they subject the hypotheses to convert them into theories.

This is what geologists assume:

  • Events in earth history leave decipherable physical evidence of their occurrence in rocks. Indeed, the characteristics that rocks display are related in an orderly fashion to the processes that created the rocks rather than being randomly stamped upon them.
  • The orderliness to the relationship between processes and their physical results provides a key to deciphering earth history. This key exists because past events obeyed the same physical laws that govern the universe today.
  • Thus, studying the way the earth works now furnishes an understanding of the characteristics of rocks and the history they represent: past rock-forming processes may be identified, the environments in which they operated may be determined, and the sequence in which they took place may be unraveled. In short, the present is the key to the past.
  • An understanding of the present may be gained by direct observation of nature and also by careful analogy between experiment and nature.
  • Prediction is reliable in principle because the physical laws that govern the universe today are independent of time and will continue unchanged into the future.


If these assumptions are not acceptable, then there is no particular reason why geologists' conclusions should be held in high regard. What is demanded of you in this course is not acceptance of the geologists' world, but an understanding of how it is constructed.

Approaching such understanding will involve learning geologists' views of:

  1. An acceptable definition of 'rock'.
  2. How in general rocks form.
  3. How the origin of a particular rock may be determined.
  4. How relative age may be determined.
  5. How absolute age may be determined.
  6. How these principles may be used to unfold the history of the earth.

© 2001, David J. Leveson