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What is
microevolution?
Relative dating uses scientific principles to
determine the age of one layer of rock as
compared with another. That is, relative dating
determines which layer is likely to be older and
which layer is likely to be younger. Although this
technique cannot determine the exact age of a
layer of rock, it is commonly used to determine
the relative age of fossils contained within rock
layers. This allows scientists to determine the
sequence of development for a variety of
fossilized organisms
What is the most
direct evidence
for
macroevolution?
Careful observation shows that the distribution of fossils
within layers of rock is not random. Fossils of organisms
such as trilobites are consistently found in layers of rock
located beneath the layers of rock containing fossils of the
first marine reptiles. Dinosaur fossils are consistently found
higher in the layers of rock than fossils of the first marine
reptiles. Analysis of these observations allows scientists to
recreate the sequence of events through which living things
came into being on Earth. Scientists interpret this
information to indicate that trilobites appeared first, followed
by marine reptiles, and then dinosaurs. Fossil succession
and the trends illustrated regarding the change in body
shape and complexity were well established and described
many years before Darwin s work on evolution by natural
selection occurred.
What does the fossil
record show? (What is
the order of evolution
of organisms in
chronological order?)
Note that the use of these
techniques makes it is possible to
determine which layers of rock are
older than others. However, it is not
possible to determine the exact age
of a rock layer. In order for the
exact age of a rock layer to be
determined, radioactive dating
techniques must be used.
Explain why the mass
extinction of dinosaurs
lead to a dramatic
increase in the number
of mammal species.
Radioactive dating is a
technique used to
determine the actual age
of a sample of rock. It is
based on the principles of
radioactive decay
What is
relative
dating?
The gradual change and
adaptation of an organism
to its environment through
small shifts in allele and
gene frequencies is known
as microevolution.
How does the
distribution of fossils
within layers of rock
offer evidence for
evolution?
Fossils offer the most direct form of
evidence for macroevolution.
Fossils have been recovered from
Antarctica to the Arctic Circle. A
high concentration of fossils are
found throughout southern Alberta,
Saskatchewan, Montana, Utah,
Colorado, New Mexico, and
southeast Australia.
How can the
exact age of a
rock layer be
determined?
The oldest fossil records indicate that simple
bacteria-like cells were present about 3.4 billion
years ago. As time passed, the number of
species increased, as well as the complexity of
their structures. The number of multicellular
species then increased dramatically. Simple
invertebrates were the first to appear. This was
followed by the appearance of complex
invertebrates about 600 million years ago. Fish
were the first vertebrates to appear, followed by
amphibians, reptiles, birds, and mammals.
What is
radioactive
dating?
The mammals that first appeared 200 million
years ago were tiny. Following the extinction of
the dinosaurs about 65 million years ago, the
number of mammals increased dramatically.
Today, there are about 4 500 mammal species.
The rapid proliferation of mammals following the
extinction of dinosaurs is an example of episodic
speciation. It is common for episodic speciation
to follow mass extinction events because the
loss of large numbers of species from the
ecosystem opens up new niches to be exploited
by those organisms that survived.