The living world in space and time

If you tried to give every living species on Earth a name, how far would you get? Scientists have already named about 2.5 million. Careful estimates put the real total between 5 and 30 million.

Today's species did not appear from nothing. Each one evolved from a species just before it, in an unbroken ancestor-to-descendant chain called a phyletic lineage.

A complete record would trace every lineage back to life's common origin. It doesn't exist, because soft-bodied ancestors rarely left a fossil behind.

Biologists still map life two ways: in space, through biomes shaped by climate, and in time, through fossils buried in rock layers and dated using radioactive isotopes.