I have spent the majority of my adult life trying to comprehend the significance of time's depth. He pointed out that Toronto is one of the worlds leading centres for the study of deep time, with several research facilities dedicated to pinning down the age of truly ancient rocks or fossils. Moreover, some new techniques have been pioneered there, such as the use of lasers to date tiny mineral grains individually, a process that in some cases dramatically improves the quality of the dating process. Walter began by noting the irony of the fact that scientists have had to look beyond the earth in order to measure this planet's age. Much older rocks were found on the moon, which is virtually inactive geologically and which is assumed to have been created from the earth.
Scientists also take advantage of natural clocks found in some mineral specimens.
One such clock is a Uranium isotope that decays at a known rate over hundreds of thousands or millions of years. Measurements of the amount of this isotope remaining in a sample can indicate when that mineral was first formed. Such information can be used in interesting ways. For instance, the impact of an asteroid in the Mexico's Yucatan Peninsula some 65 million years ago is believed to have been a catastrophic event that led to the extinction of the dinosaurs. The collision blew a great deal of material into the atmosphere, debris that circled the globe at least twice.