In the latter half of the 20th century, earth-scientists gradually became aware of the scale and effect of bombardment by meteoric material on Earth. Prior to 1950 only a handful of small craters were generally accepted as resulting from impact events. Now "certain" impacts number around 150, with four such features measuring over 100km in diameter. In this book, Neville Price evaluates the mechanisms that give rise to plate movements. Generally, such plates move slowly at about the rate of growth of human nails and their tracks are usually smooth, gentle curves. This text presents evidence to show that impacts can cause significant and dramatic changes in track, which cannot be explained by current theories of plate tectonics. It also demonstrates that such major impact events often coincide with the development of continental flood basalts and oceanic plateau basalts and frequently coincide with major stratigraphic stage boundaries and toxicity, which in turn can be associated with periods of extinction.
It concludes that geological history comprises periods of relatively orderly, evolutionary change in Earth and life-forms punctuated by catastrophic changes induced by major impacts that reset the evolutionary clock.