A Toxic Explosion
For more than 4 billion years, evolution didn’t produce more than soft-bodied aquatic life such as bacteria, plankton and algae, but in the Cambrian era 570–500 million years ago, the fossil record paints a newly diverse picture. Life bloomed, creating the lineages of almost all animals alive today, most notably organisms with hard shells and skeletons. This event is called the Cambrian Explosion, and the question is—what spurred on these immense and sudden changes? The geological record of the era is confusing and discontinuous, but it gives us clues to the answer. Millions of years worth of rocks from directly before the Cambrian era seem to have disappeared, as the sedimentary rocks of the Cambrian era lie directly above a far more ancient layer (check out the stark difference in the photo). Researchers have proposed that these disappearing rocks were actually dissolved into the ocean. The exposure then released minerals like calcium, iron, potassium, changing the ocean’s chemistry to become more alkaline—and the result was toxic. This could have acted as a catalyst for the massive evolutionary burst: in order to survive the mineral imbalance, organisms began to use them to form biominerals like calcium phosphate and calcium carbonate, forming bones and shells respectively.