C hapter 2: Geological Time - PowerPoint Presentation

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

.Slide31
Slide32

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

AnswersSlide34
Slide35

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