Geology Reference
In-Depth Information
beginning of the Phanerozoic Eon 542 million years ago (see
Chapter 21).
Animals
ROCKS
A variety of resources are found in Precambrian rocks, but
the one most often associated with rocks of Archean age is
gold, whereas iron ore is the one that comes to mind when
we discuss Proterozoic resources.
Higher plants
Amoeboflagellate
ancestor of protozoa
and fungi
Blue-green
algae
Mitochondria-
containing
amoeboid
Spirochetes
Archean and Proterozoic rocks near Johannesburg, South
Africa, have yielded more than 50% of the world's gold since
1886; but Archean gold is or has also been mined in the
Superior craton in Canada and the Homestake Formation in
South Dakota. Several Archean-age massive sulfi de deposits
of zinc, copper, and nickel are known in Australia, Zimba-
bwe, and Canada, and similar deposits are currently forming
adjacent to black smokers on the seafl oor (see Chapter 9).
About one-fourth of the chrome reserves are in Archean
rocks, especially in Zimbabwe; they probably formed along
Prokaryote host
Aerobic bacteria
◗
Figure 19.24
Endosymbiosis Theory for the Origin of Eukaryotic
Cells An aerobic bacterium and a larger host united to form a
mitochondria-containing amoeboid. An amoebofl agellate was formed
by a union of the amoeboid and a bacterium of the spirochete
group; this amoebofl agellate was the direct ancestor of the three
kingdoms—protestan, fungi, and animalia. The plant kingdom
originated when this amoebofl agellate formed a union with
blue-green algae that became plastids.
a
The affi nities of
Tribachidium
remain uncertain. It may be
either a primitive echinoderm or a
cnidarian.
b
Spriggina
was originally thought to
be a segmented worm (annelid), but
now it appears more closely related to
arthopods, possibly even an ancestor
of trilobites.
c
Shield-shaped
parvanconrina
is
perhaps related to the arthropods.
d
Reconstruction of the Ediacaran environment.
◗
Figure 19.25
The Ediacaran Fauna of Australia
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