Environmental Engineering Reference
In-Depth Information
The Past as Proxy for the Future
u
.
A Short Tour Through
.
Billion Years
The global warming debate is about what will happen in
the next few hundred years. Our planet Earth is
.
billion
years old, and over the planet
s lifetime changes in tem-
perature, greenhouse gas concentration, and sea level
have occurred that dwarf any of the changes being
discussed now. Life is thought to have begun roughly
'
billion years ago, perhaps earlier, with bacteria-like
organisms whose fossils have been found and dated.
They lived in the oceans in a world with only traces of
or perhaps even no oxygen in its atmosphere. It was about
.
first algae capable of photo-
synthesis started putting oxygen into the atmosphere,
but to a level of only about
.
billion years ago that the
%
of today. All the creatures of the time were small. This
earliest period is largely a mystery that is still being
unraveled. Recent work indicates that it was only about
% compared with the
million years ago that the oxygen concentration in the
atmosphere rose to anything like today
s values
and
'
larger plants and animals appeared.
The University of California
s Museum of Paleontology has an excellent
interactive section on the history of the Earth and the rise of life. See
A more technical but readable article on the rise of oxygen is by Don
Can
'
eld et al.[
].
