17 - Bones of our ancestors

Summary

We are interested here in the place of life in the history of the earth more than in the history of life itself. For this, we need, besides an elementary understanding of the organization of life and of the theory of evolution, a brief account of the course of evolution through time. Armed with that we can then turn to life's conquest of the sea, the land and the air (Chapter 18), and the sudden expansions and large extinctions (Chapter 19) that raise many questions. These questions range from the scientific to the philosophical and metaphysical and have a large impact on our view on the history of our planet.

EDIACARA!

Late in the Proterozoic, during the Vendian period, an accident of fossilization preserved a rich fauna of soft-bodied organisms in the Ediacara beds of Australia and elsewhere. The Ediacara fauna consists of the first large, multi-celled fossil animals (Metazoa). They were already built on several different ground plans and bear witness to a rapid diversification just before the Phanerozoic began. The Vendian, dated between 610 and 570 my according to the time scale adopted for Figure 2.4, is probably somewhat younger and the beginning of the Cambrian therefore that much later (Figure 17.1).

The imprints of the Ediacaran bodies are not their only remains. Metazoa crawl, walk about, or burrow, and so leave tracks and holes that are often more easily preserved than the animals themselves.