The Cambrian explosion saw the rapid evolution and emergence of various life forms. However, geologists claim that organisms belonging to some major phyla already diversified prior to the Cambrian period, with further evidence suggesting that the evolutionary process at that time was gradual, rather than explosive.
The Cambrian explosion, otherwise known as the Cambrian radiation, occurred during the Paleozoic era. Scientists believe that various factors may have triggered the sudden change, including an increase in oxygen levels, a shift in climatic conditions and the creation of more habitable environments. Some animals that flourished during the Cambrian period were the brachiopods, arthropods, nematodes, fungi and chordates, to which the human species belongs.