us at nearly the speed of light.The beginning universe might have rapidly bal-
looned outward for an instant, a phenomenon called inflation, and then set-
tled down to a steady growth. The expanding fireball required perhaps
300,000 years to cool sufficiently to allow the basic units of matter to clump
together to form billions of galaxies each containing billions of stars (Fig. 1).
The first galaxies evolved when the universe was about 1 billion years old and
only about a tenth of its present size.Figure 1The Andromeda
galaxy is one of the
nearest spiral galaxies to
our own Milky Way.
(Photo courtesy NOAO)
Historical Geology