Question

What theories explain the Cambrian explosion?

What were animals like before the Cambrian time period?

Answer 1

• Cambrian explosion is an example for the evidence of first bacterial forms living on Earth date back to 4 billion years ago.
• It took nearly 2 billion years for these unicellular organisms to get it together, as they say, and become multi-cellular.
• After 500 million years ago nearly every animal phylum that exists today had evolved and diversified to some extent.
• This was quick jump for a slow and gradual process.The sudden appearance of diverse life in the fossil record baffled scientists and even caused Darwin to question his theory on evolution by natural selection. They called this the Cambrian Explosion.
• The only modern phylum with an adequate fossil record to appear after the Cambrian was the phylum Bryozoa, which is not known before the early Ordovician.

Early animal life (Ediacaran biota) evolved from protists during the pre-Cambrian period, which is also known as the Ediacaran period. It was previously believed early animal life included only tiny, sessile, soft-bodied sea creatures, but scientific evidence suggests more complex animals lived during this time. Some protist species called choanoflagellates closely resemble the choanocyte cells in the simplest animals, sponges. In addition to their morphological similarity, molecular analyses have revealed similar sequence homologies in their DNA.