Fossils
S
D. Crowley, 2008
Fossils
To know how fossils are formed and how they provide evidence for
evolution
How are fossils formed?
S How do you think the following fossils were formed?
S What types of rock do you think they are found in?
Making Fossils
S Use a shell to make an imprint into a lump of plasticine.
S Fill the mould with plaster of paris and leave to dry.
S At the end of the lesson you can peel the plasticine away
from the plaster and you will have your own fossilised
imprint!
Fossils
What are fossils?
S As soon as plants and animals die they begin to rot away – however,
sometimes the dead plants and animals can be turned into fossils (rock
copies of the original plant or animal)
S Fossils forms when dead plants or animals become
covered in a layer of sediment which initially
protects them…
Fossils
S An organism dies, and settles on the sea floor
S Gradually it is covered with sediment which protects it, and over time
the layers build up
S As the layers build up the pressure increases, causing sedimentary rock to
form
S The dead organism undergoes a series of chemical changes resulting in
rock-like minerals taking the place of the original chemicals
S Over millions of years the original organism is replaced with minerals,
and a rock-like copy of the organism is left
Fossil Formation
Fossils can be formed in a couple of ways…
S
Some are stone copies of the organism, formed as the organism become petrified
(turned to rock) by the deposition of minerals in the tissues as they decompose
S
Other fossils consist of impressions of the organism's shape, left behind in the
surrounding stone as the tissues decompose
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Most dead organisms decay very rapidly and their tissues are recycled, leaving no
trace of their existence, but certain environmental conditions drastically slow
down the decay process, thus helping to preserve the tissues, for example: S Insufficient oxygen (organism trapped in resin, e.g. amber)
S Low temperatures (organism frozen in glacier)
S High soil acidity (organism in peat bog)
Design a cartoon strip to
explain how fossils are formed
S Everyone must produce a unique piece of work
S A cartoon in five panels describing the stages in fossil
formation (L4)
S A conclusion explaining where you are most likely to
find fossils (L5/6)
S An evaluation of why the formation of fossils is
rare/but why fossils are quite common in some rocks
(L6/7)
Dating
Where would we find the earliest fossils?
The earliest fossils are found in the
deepest parts of the rock (over time more
and more sediment is laid down, meaning
organisms which dies the longest time ago
are found in the deepest parts)
What does this provide evidence for?
Evolution
S How has our understanding of fossils over the past few hundred years led
to a better understanding of evolution?
S Most of the evidence for evolution comes from rocks and fossils – fossil
remains have been found in rocks of all ages: -
S Fossils of the simplest organisms are found in the oldest rocks
S Fossils of more complex organisms are found in the newest rocks,
S This supports the evolutionary theory that simple life forms gradually
evolved into more complex ones, and that all animals have gradually
evolved from a common ancestor
Evidence for evolution
S http://espresso/espresso/clipbank/servlet/link?macro=setr
esource&template=vid&resourceID=2524
Evolution
S Is it that simple?! What problems can you identify with fossil evidence
being used solely as evidence for evolution?
S Rocks move around, so you don't always find the newest rocks near the
surface, or the oldest rocks deep down
S Evolution is not always an orderly progression from simple to evermore
complex organisms - it goes in fits and starts
S Building up the story of evolution of any one species is difficult, as in most
cases there are big gaps in fossil records (it can be like putting together a
jigsaw puzzle with half the pieces missing)
Human Evolution
S Humans evolved from apes, however evidence for this transition is not
abundant when we look to fossil records
S The evolution from ape to modern man was by no
means instantaneous, yet fossil evidence of how
man gradually changed is still vastly incomplete –
we are still in search of the ‘missing link’…
S *Humans did not evolve from chimpanzees or any
other modern ape – they are instead closely related
organisms, probably all sharing a common ancestor
Using fossil evidence to find out
about “the hobbit”
The Hobbit people
S
Remains of small humans were
discovered in 2003 on the island of
Flores in Indonesia.
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Scientists think Homo floresiensis is
a possible human species, now
extinct
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Partial skeletons of nine individuals
have been recovered, including one
complete skull.
Artist’s reconstruction
Write about hobbits using
dig evidence. Complete for
your homework.
Mammoth tooth
•
Here are some questions to help
with your writing.
•
What sort of things might hobbits
have eaten? Why? (L5)
•
How long did hobbits live on the
island of Flores? (L5/6)
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What tools did hobbits use? (L5)
•
What might have caused the
extinction of hobbits? (L5/6)
•
What did hobbits use for shelter?
(L6)
•
What evidence is missing? Why?
(L6)
•
How certain are you of your
explanations? Why? (L7)
Mammoth bone
with cut marks
Human Evolution?
Fact Opinion or Speculation?
S “Dinosaur Fossils found in South America”.
S 147 fossils have been found.
S “Scientists think the discovered fossils may be from a dinosaur related to
the Stegosaurus as the bones are similar”.
S Scientists have dated them 200 million years old using carbon dating
techniques.
S Scientists think there could be up to another 100 fossils in the area
S Mr Robinson says they ate turtles.
S Three German scientists disagree with Mr Robinson and think they were
vegetarians.
S They were probably land animals not water based on the bones they have.