The Big Bang Never Happened

THE ENDLESS FLOW OF TIMEFig. 7.4. The development of multicellular life over the past six hundredmillion years can be roughly measured by the number of families oforganisms found in the fossil record. This graph, compiled by Jack Sepkoski,shows the general increase in the number and variety of life forms,punctuated by sharp crises as one mode of life reaches its limits and issucceeded by another. The sharpest crisis was 250 million years ago, justbefore the rise of the dinosaurs and other land-dwelling species. The crisisthat Jed to the dinosaurs' extinction sixty-five million years ago wasrelatively milder.From this, a third major change was the development of landdwellingplants and animals—ferns and amphibians. Thisopened up huge new resources of energy. Sea-dwelling creaturesare far more numerous in areas near the shore, where nutrientsand sunlight are both available. Even today the deep ocean is anear desert compared with coastal waters. The land, in turn, providesboth sunlight and nutrients over a much larger area. Amphibians,however, were limited to coastal areas, because theirreproductive cycles still required the temperate environment ofthe oceans.The next great revolution gave birth to reptiles, which nolonger needed to live in proximity to water and so could liveanywhere on land. They too—even the giant dinosaurs—werelimited by their inability to survive rapidly changing tempera-305