relates the discovery of extremophiles—bacteria that thrive in
harsh subterranean and deep ocean environments similar to those believed to
have existed on primitive Earth.
describes an attempt to determine when life began on Earth by searching
rock formations in Greenland for higher-than-expected ratios of carbon 12 to
carbon 13 (in ratios currently only known to be created by life processes).
points to the comets and meteorites that struck Earth during its early
history as possible sources for the carbon and other ingredients necessary for
life to form.
reveals the discovery of amino acids (organic acids that form the
proteins that are essential to life) in meteorites.
describes an experiment that simulated a comet's massive impact with
Earth to determine whether certain amino acids could have withstood such a
indicates experimental results that show that the amino acids not only
could have survived but also may have fused into peptides (compounds formed by
linking two or more amino acids).
speculates that life may have begun deep in Earth's crust or oceans,
where it would have been protected from harsh solar radiation, the high
temperatures of Earth's surface, and bombardment by meteorites.
uncovers bacteria living deep below Earth's surface that obtain energy
from methane, ethane, and propane gases and suggests that ancient bacteria
might have derived energy in the same way.
notes that surface bacteria that emerged following the Great Bombardment
likely developed the ability to photosynthesize.
looks at stromatolites—both modern ones built from layers of
cyanobacteria and sediment and their fossil counterparts that may have formed
the same way—and reviews the role the cyanobacteria played in creating an
oxygen-rich environment in which complex life could form.