A Walk Through Time

Silicon Symmetry

Triassic-Jurassic Mass Extinction

208 Million Years Ago

Just 37 million years after the Permo-Triassic mass extinction, the Triassic Period comes to an end with another mass extinction. It will require 100 million years for biodiversity levels to recover from the combination of these two neighboring devastations of life.

New species evolve. Diatoms with magnificent silica microshells appear and spread quickly throughout the seas. These micro mineral-magicians extract and cycle silica and other elements from the oceans.

Before these creatures evolved, the oceans were supersaturated with soluble silica. As each silica-forming group arose, silica concentrations decreased. Major accumulations of biogenic opal begin to cover the ocean floors of the world.

Top: Each spine in this colonial diatom comes from an individual diatom cell. At one end of the colony, one cell operates as a steady grip, while all of the other cells float in the current and collect nutrients to share. (Photograph by R. George Rowland, courtesy Marine Biological Laboratory, Woods Hole)

Bottom: These diatoms are mating. The gametes (reproductive cells), having left their silicious tests (the flying-saucer-shaped shells in the background) are about to fuse. (Photograph by Jeremy Pickett-Heaps)

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