gems, geology, East Africa, Kenya, Tanzania, Mozambique belt, Gondwanaland, Cambrian explosion, origins of life, origins of multicellular life

For the first 80% of the fossil record, some 3000 million years, fossil animals are exclusively single-celled, apart from simple filamentary and sheetlike forms, suggesting that the evolution of complex animals with specialized, interdependent cells (i.e., Metazoa excluding coral-like organisms) was long delayed by a pervasive obstacle; yet when multicellular animals finally emerged around 540 million years ago during the Cambrian Explosion, they did so with remarkable diversity, abundance, and suddenness, producing many new phyla including organisms with mineralized spicules, external sclerites, conches, tubes, “teeth,” carapaces, and structural reinforcements—not merely variations on one biochemical theme but incorporating chitin, phosphates, calcite, aragonite, silica, organic matter, and even agglutinated sand (Lipps and Signor, 1992).