We have discussed the Last Universal Common Ancestor (LUCA). LUCA was a single cell that lived perhaps 3 to 4 billion years ago. We don't know how this cell arose, although there are many ideas. As far as scientists can tell, this was the only event on Earth where organic life arose in an inorganic setting.
It does seem clear that all life evolved from this single cell, although it's taken many twists and turns along the way. The study of evolutionary twists and turns, the ancestry of organisms, is called phylogenetics.
Phylogeny is the study of evolutionary relationships among organisms. Below is an example of a phylogenetic tree from a common ancestor of cats, skunks, otters, domestic dogs, and wolves: