ABSTRACT
Charles Walcott suggested just that: as whole islands have been built by corals, those domes and pillars had been left behind by precambrian microorganisms. Walcott found mounds, domes and pillars of various dimensions and shapes which had unique characteristics: they were made of wafer-thin layers, and were definitely precambrian. All over the world there are rocks from the middle Precambrian which consist of alternating layers of iron-rich and iron-poor silica, and these represent a planetary transition between two distinct phases in the geology of iron. In order to appreciate the other problems that life had to solve in the Precambrian, we need a few concepts from the history of science, starting from observations made by the microscopists of the 18th century. The cells had gone, but the minerals deposited on them had solidified and had become the stony replicas of the colonies. The cells obtain energy by three mechanisms—fermentation, photosynthesis and respiration—and fermentation is by far the simplest of them.
