Travel Reference
In-Depth Information
This apparent dull uniformity masked a great deal of evolutionary activ-
ity that gave rise to some of life's most essential capabilities. Many dif erent
kinds of bacteria evolved soon after the fi rst appearance of life. Some of them
were able to photosynthesize, and some lineages of these bacteria eventually
bequeathed these abilities to multicelled organisms that became the higher
plants. As a result of these new ways of manipulating the environment to
extract energy, the very chemical composition of the atmosphere and the
oceans gradually changed, making the world's environment more like that
of the present time.
Very little of this activity has been preserved in the fossil record. A few
traces of possible bacteria may have been found in Australian rocks as old
as three and a half billion years, although the exact nature of these early fos-
sils is embroiled in controversy. Stromatolites were plentiful throughout
the early history of life, but the oldest ones do not show clear signs of being
built by layers of bacteria and may have simply been the result of geological
processes.
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About 625 million years ago this superfi cially rather boring world of liv-
ing organisms began to change. A scattering of modest-sized and extremely
odd creatures with no obvious ai nity to present-day organisms began to
leave traces in the fossil record. These mysterious creatures make up the Edi-
acaran biota, named after regions in Australia where they were fi rst found.
Even this collection of creatures, exciting though they were in compari-
son to the dull bacterial communities of earlier times, would have seemed
tures dotted the sea bottom like waving feathers, and strange fl at creatures
slithered among them, most of the Ediacaran organisms, like those that pre-
ceded them, were still too small to be seen with the naked eye. And yet, as
we will see, this simple world might have provided an environment for evo-
lutionary experimentation that would not have been possible during either
earlier or later times.
Then, 542 million years ago, at the start of a geological period called the
Cambrian, everything changed. Starting with a burst of small shelled mol-
lusks, a multiplicity of animals soon appeared, presaging a world more like
