Geology Reference
In-Depth Information
This finding illustrates a truth about biological classification that scientists have slowly been discover-
ing: Common physical characteristics are not the strongest line of evidence for drawing conclusions
about evolutionary relationships. Currently, scientists accept the classification of all living things into
the three domains of Bacteria, Archaea, and Eukarya instead of the six kingdoms.
Stromatolites still exist today but are rare. One place they can be found is in warm, shal-
low, extremely salty ocean water, such as in Shark Bay in Western Australia, which is pic-
tured in the color photo section. This environment is inhospitable to other creatures
that might eat the algae, so the algae flourish without any predators.
Scientists think that the algae that built Archean and Proterozoic stromatolites are
largely responsible for the photosynthesis that added oxygen to the atmosphere.
Waiting to inhale: The formation of earth's atmo-
sphere
The earth's early atmosphere originated from volcanic
outgassing,
or eruptions of gas
and water vapor. The gasses that filled the atmosphere included water (H
2
O) and car-
bon dioxide (CO
2
) with very little “free” oxygen (O
2
). There are two ways to separate
oxygen from water and carbon dioxide molecules: photosynthesis and photochemical
dissociation. In the previous section, I cover photosynthesis (courtesy of cyanobacter-
ia).
