Fossils Fossils provide a window into the past as they provide evidence about the changes that have occurred to the Earth over the 45 billion years of existence A fossil is the preserved evidence in rocs or soils of organisms that once existed on Earth ID: 576335
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Slide1
Chapter 2: Geological Time Slide2
Fossils
Fossils provide a window into the past as they provide evidence about the changes that have occurred to the Earth over the 4.5 billion years of existence.
A
fossil is the preserved evidence in rocs or soils of organisms that once existed on Earth. Fossils may be the whole body, part of the body or traces of its activities.
2.1 - FossilsSlide3
Fossils.
To be preserved as a
fossil
the organism must decay very slowly.Occurs when the organism is covered in sediment, which then turns to rock.A palaeontology is the study of past life.Slide4
Formation of Fossils
Animals that are only composed of soft parts such as jellyfish, slugs etc. are rarely found as fossils.
Hard objects such as bone, tree bark, shells and teeth are most likely found as fossils.
The following process is how fossils occur in sedimentary rock.Slide5
Fossil Formation
Fossils are found only in sedimentary rock not in igneous or metamorphic rock as the heat and pressure used in formation destroys the organism.Slide6
Types of Fossils
There are different types of fossils due to the different ways in which they are formed.
Types of fossils:
- Original fossils - Replacement fossils - Carbon Film fossils - Indirect fossilsSlide7
Original Fossils
Occur when a part of the organism is preserved and its composition is almost the same as when it was alive.
Most commonly skeletons, bones, teeth, shells; this is because they are harder to break down and scavengers find them difficult to eat.
Common original fossils include: - Sea creatures that had shells, such as mussles and oysters-
Verterbrates, because they had teeth and a bony skeleton, such as megafauna – the three meter tall giant kangaroo, sheep sized echidnas, 3 metre long wombats.Slide8
Original FossilsSlide9
Replacement Fossils
A
replacement fossil
occurs when a part of the organism is chemically changed into another mineral.Commonly occurs when calcium carbonate, from bones and shells, turns into another mineral such as silica.Slide10
Carbon film fossils
A
carbon film fossil
occurs when a dead body partially decays and leaves behind a thin black deposit of carbon. The traces of carbon left are often in the shape of the organism that decayed and often show fine details.Slide11
Indirect fossils
An
indirect fossil
is not part of the organism but is the preserved remains, such as imprints of the body like footprints, fossilised dung and burrows.Dung and Burrows are sometimes called trace fossils.Slide12
Preserving environments
The environment in which the organism dies can influence the fossil produced.
These preserving environments include:
- Permafrost - Amber - Tar - Peat
- Dry airSlide13
Permafrost
Near the artic circle the land is permanently frozen.
Provides the perfect environment for fossilisation as the decaying process is stopped due to the temperature being below freezing.
This environment is best for original fossils.Slide14
Amber
Amber
is a solid plant sap or gum
Insects, spiders or small vertebrates such as lizards and frogs get stuck in the sticky sap which seeps out of treesWhen it sets it perfectly preserves whatever has become stuck inside it.Slide15
Tar
Tar
pits occur when oil seeps naturally from the ground into the surface.
This preservation is rare, but when it is achieved, provides fantastic preservation. Slide16
Peat
Peat
is the partly decomposed remains of plants and is commonly found in swamps and bogs.
The peat contains acids making the hard tissue, such as bone, very soft.In Europe ancient human bodies have been found preserved in peat.Slide17
Dry Air
Extremely dry conditions, reduce the number of bacteria that are able to decay the organism therefore; Dehydrates the soft tissue which fossilises and turns it into a “mummy” (
muffication
). Slide18
Dating techniques
Relative Dating:
Compares the age of a fossil or rock with others to
determine which is older
. Absolute Dating:
Determines
the
actual age
of the fossil
Stratigraphy
Radio
active Dating
Fluorine Analysis
Tree Rings
2.2 – dating techniques
Palaeontologists use several techniques to decide the age of a fossil.Slide19
Relative Dating
Relative dating
relies on two factors:
Sedimentary rock layersFossils are the same age as the rocks they are found in.Slide20
Layers of sedimentary rock
Sedimentary rock
forms in layers called stratum
The first layer (base) is the oldest and the top is the youngest.
Relative datingSlide21
Stratigraphy
Index fossils
within the rock layers can be used to determine the relative ages depending on the rock layer they appear in
Layers A3, B1 and C5 contain the same long shell-like fossil species. Hence, these layers are the same ageSlide22
Site C has four layers about C5. This states these layers are younger than C5 (because C5 is on the bottom).
C1 is the youngest layer because its at the top
B5 is the oldest layer because it is at the bottom compared to all sites
A5 and B4 are the same age because they have the same fossil type Slide23
Index Fossils
Fossils
that can
be used to compare the ages of strata in different locations are called index fossils. To be used as an index fossil, the
species must:have been fairly widespread in where it livedhave lived in a fairly narrow period of timehave
been abundant (there were many of them)
be
easy to identify.
Relative datingSlide24
Fluorine analysis
Fluorine analysis
compares the amount of fluorine in different bones found in the same rock.
Bones absorb the flourine from water over long periods of timeThis happens slowly therefore the more fluorine the older the bone.
Relative datingSlide25
Radioactive dating
Radioactive dating
is a method that uses the
natural rate of decay of radioactive isotopes.The amount of decay allows scientists to estimate how long, before discovery, the rock was laid down.Half life is
the time it takes for half of a radioactive sample to decay
Absolute datingSlide26
Absolute datingSlide27
Carbon-dating
Carbon dating is most useful when dealing with
organic matter (proteins)
Carbon dating
is useful as far back to less than 40 000 years. Beyond that, however, the method is not very
reliable as the amount of carbon-14
remaining is
too small to measure.
potassium–argon
dating
potassium–argon
dating is most useful in rocks containing
volcanic ash Slide28
Tree rings
A useful method for dating wood.
This process involves counting the growth rings in the trunk of the tree.
Many trees grow by adding a woody layer around the stem.1 ring = 1 year
Absolute datingSlide29
Propose a suitable dating method for each of the following:
Question
Showing that two
bones
were not from the same caveProving a piece of wood was about
30,000
years old
Dating
a
wooden box
found in an Egyptian tomb
Dating a primitive stone tool found next to a
volcano Slide30
Answers
Fluorine
analysis
will show that the fluorine level was different in the two fossils.Radioactive dating using carbon since it is accurate for organic material of dates less than 50 000 years
.Tree ring dating or radiocarbon dating.
Radioactive
dating
using potassium–argon
.Slide31Slide32
AnswerSlide33
Identify the oldest layer across all four sites
Explain your reasoning:
Identify
the youngest layer across all four sites
Explain
your reasoning:
List
the strata that is the same age as D5
List
the strata that is the same age as A1
List
the strata that is the same age as
B1
C3
Because its the bottom layer
Because its the top layer
D1
A4, B3, C1
D2
A2, D3
AnswersSlide34Slide35
AnswerSlide36
Identify
the oldest layer across all four
sites
Explain your reasoning: Identify the youngest layer across all four sites Explain your reasoning:
List the strata that is the same age as C3 List the strata that is the same age as B4
List
the strata that is the same age as D4
Which
layer in location B appears to be missing from location
D
Because its the bottom layer
Because its the top layer
A
3
D1
A2
A1, C2
B3, C1
D2
AnswersSlide37
2.2 Unit Review (page 53)
Q1,2,3,4,5,6,7,9,10,
15
Homework