Fossils as Clues / Post Lab
Was Wegener Correct???
At any given moment, every
place on Earth is either
erosional or depositional.
The geologic history of the Earth is
written in layers of sedimentary rocks.
• Deposition of sediments records (writes)
history.
• Erosion erases records that were
previously written.
• Geologists can open the book to read by
drilling core samples and examining rock
columns.
What does finding coal in
Antarctica tell you?
• Antarctica was once warm and rainy with
swamps.
• How could that be?
• Either the whole world was once warmer
(global warming) or
• Antarctica used to be located near the
Equator (AND IT MOVED SINCE THEN!)
What does finding two different places
with the same sequence of sedimentary
rocks tell you?
• They both had the same sequence of
environments (and environmental
changes.) (BUT, Not necessarily at
the same time.)
If two places have rocks indicating
that the same things happened in
each (for example - an ocean dried
up), how would you know if both
happened at the same time?
FOSSILS
What about present and
past plants and animals?
• Today, there is a rule in biology that says
that each continent has its own land plants
and land animals.
• Fossils tell us that India, South America,
Antarctica, and South Africa all had the
same plants and animals at one time.
• WAS THE RULE BROKEN?
• Why or why not?
OK - So why did we do all of this????
• Alfred Wegener said that it wasn’t a
coincidence that the continents look like
pieces of a jigsaw puzzle.
• He thought that the continents had, at one
time, all been connected.
• Most other geologists thought that
Wegener was wrong.
• Wegener started to gather evidence to
support his hypothesis.
• Now we will review some evidence and the
conclusions you can draw from this evidence.
TEST!
Evidence
1.
2.
3.
4.
Conclusion
EVIDENCE - CONCLUSION
• 1. Some continents have
rocks that indicate that
they once had environments
very different from
environments those
continents have today.
• For example - Antarctica
has coal.
• Antarctica was once
near the Equator
(when it formed coal)
and has since moved to
the South Pole.
• Therefore,
CONTINENTS CAN
MOVE!
EVIDENCE - CONCLUSION
• 2. Sedimentary rocks in
rock columns show that
continents that are now
widely separated had
the same sequence of
environments.
• India, Antarctica,
South Africa, and
South America were
once connected and
so, share the same
history.
EVIDENCE - CONCLUSION
• 3. Fossils in the
sedimentary rocks tell
us that not only did
these continents have
the same sequence of
environments, they
each had the same
environment at the
same time.
• This is additional
evidence that
India, Antarctica,
South Africa, and
South America
were once
connected.
EVIDENCE - CONCLUSION
• 4. Today, each
continent has its own
land plants and land
animals. (A rule!)
Fossils show that many
of today’s continents
once had the same
plants and animals.
• India, Antarctica, South
Africa, and South America
were once connected. The
rule wasn’t broken because
there was only one
continent (and it had its
own plants & animals.)
How do geologists know what
environments existed in the
past?
•
•
•
•
Sedimentary Rocks!
Coal = swamps
Sandstone = beach, dunes, or riverbank
Limestone = deep ocean
How do geologists know when
things happened?
• Fossils!
• Certain plants and animals only lived on
Earth for a short period of time.
• If you find a fossil of one of those
organisms in a rock layer, you know how old
that layer is.
• Lystrosaurus was early Triassic.
You find several layers of sand
exposed in a river bank. Which is
the oldest layer?
• The one on bottom.
• You know this because of the principle of
superposition.