The oldest signs of life on Earth are fossilized ancestors of these one-celled organisms
Evidence of the single-celled ancestors of animals, dating from the interval in the 
... All life evolved from a single-celled universal common ancestor, and at various 
times in Earth history, single-celled organisms threw their lot in ... that these 
fossils represented the embryos of the earliest animals -- much of... [DOC] [TLE] Workshop: The Evolution of Cells [PAR] The first living things on earth were simple, single-celled organisms enclosed by 
a plasma membrane.