Question: what was the first animal on earth?

Sara Imari Walker answered on 18 Jun 2011:

Hello Maranna! The very first living creatures on earth with single-celled microbes, that lived over 3.5 billion years ago. Things we would call animals arose much much later. Multicellular organisms first appeared around 1.2 billion years ago. These organisms mostly consisted of cell colonies of limited complexity as Drew stated. The first true animal lineages to diverge (if you define an animal as a multicellular organism – Drew is right definitions are important!!) were sponges and comb jellies. Now this doesn’t tell us that the first animal was a sponge or a comb jelly, but it does tell us that comb jellies and sponges are closely related to what that first animal was. So we can find out a lot about the first animals by studying these simple creatures!