In this wonderful six-part series Philip Morrison (MIT) presents science on a human scale. Ring of Truth was produced and is copyright 1987 by Public Broadcasting Associates, I'm putting it online because it exists in no modern format.

Clues presents another key to the way science works: reconstructing the past with the evidence of the present. To illustrate this, Morrison follows a geologist who uses a simple hammer to test a sample and infer the history of Amethyst Mountain in Yellowstone National Park. For the rest of the intriguing story, an elaborate computer-controlled drill ship if required to piece together the clues to a new and dramatic hypothesis: that five million years ago the Mediterranean Sea was an arid salt desert formed as the Straits of Gibraltar closed into a huge natural plug that shut off the Atlantic waters.