Transcript: The development of multicellularity was very important in the evolution of life, and it spurred the adaptive process of natural selection. There is evidence that multicellular organisms developed independently in several branches of the eukaryotes. However, about five hundred and fifty million years ago, in the oceans of the Earth, something extraordinary happened. This was the start of the Cambrian era, and it dates to a time when there was an extraordinary flowering of life forms in the oceans of the Earth. The diversity in the Earth’s oceans lead to almost all the major body plans of life that we see now, occurring only in a one percent span of the Earth’s history starting five hundred and fifty million years ago. Biologists talk about the body plans of organisms by grouping them in phyla. The level above this are kingdoms, such as the plant kingdom and the animal kingdom. The Cambrian explosion saw the development in a short period of time of thirty or more phyla, including for example the arthropods which includes insects and spiders and the chordates which include mammals and reptiles. This flowering of life in the oceans of the Earth was facilitated by the rise in oxygen in the Earth’s atmosphere and probably by the fact that there were not a lot of predators at the time of the first diversification.