Carl Zimmer's blog, The Loom, features this image with better resolution. It comes from biologists at the European Molecular Biology Laboratory, who have published in Science the most thorough tree of life based on sequencing 31 universal genes selected from 191 species of animals, plants, fungi, protozoans, bacteria, and archaea.
Zimmer explains the diagram:
It's amazing how small the animal kingdom is in the picture--if "speciesism" is a real problem, People for the Ethical Treatment of Animals (PETA) are apparently guilty of it by focusing only on animals.
Here's a quick tour of the tree. Start at middle of the circle. The central point represents the last common ancestor of all living things on Earth. The tree sprouts three deep branches, which between them contain all the species the scientists studied. These deep branches first came to light in the 1970s, and are known as domains. We belong to the red domain of Eukaryota, along with plants, fungi, and protozoans. Bacteria (blue) and Archaea (green) make up the other two domains.
These lineages probably split very early in the history of life. Fossils of bacteria that look much like living bacteria turn up at least 3.4 billion years ago. Just a few lineages became multicellular much later, with some algae getting macroscopic about two billion years ago.
The length of the branches on this tree represent so-called genetic distance. The longer the branch, the more substitutions have accumulated in its genes. Since these genomes all come from living species, the branches all span the same period of time. The fact that some branches are long and some are short means that some lineages have evolved more than others. Many forces can stretch out genetic distance. A species may reproduce fast, or it may have a life that makes it prone to acquiring more mutations. The slash in the Bacteria branch represents a segment that the scientists left out to make the full tree easier to see.