The document discusses methods for determining the age of the Earth by examining fossils and rock layers. It describes how fossils are formed by rapid burial after death, and how studying the layers they are found in can reveal the conditions of the Earth during different time periods. Index fossils that are unique to a specific layer are useful for correlating the ages of different rock formations. The fossil record also provides evidence that species have evolved over long periods of time. Radiometric dating techniques allow scientists to directly determine the ages of rocks and provide evidence that the Earth is very old.

1. Finding the age of earth
Chapter 12
Chemistry

2. Layers
of
rock

3. How fossils form in rocks
- Fossils are the remains of once living things.
- Most fossils are formed from plant and animal
bodies.

4. 1) Animals or plants covered quickly after death (stops
scavengers ripping up the body)
2) Covering contains little air and oxygen (decomposers
cannot thrive and rot down the body)
3) Sediments harden to form rock
4) Tissues of the body in the
rock is replaced by chemicals in
water passing through rocks
(replacement)
5) Water containing dissolved
minerals seeps into the tissues.
The minerals strengthen the
tissues into rock (petrification)
OR

6. Trace fossils
- Things left behind
EX. Eggs, droppings and tracks.

7. How ideas changed about fossils
Ammonite
- This ammonite fossil was first
thought to be curled up bodies of
stone snakes.
- Later they were found to be the
shells of creatures related to the
octopus, which swam in ancient
seas.

8. - The word fossil was first used by Georgius
Agricola (1494 – 1555), a German doctor.
- He used the word to describe anything that was
dug out of the ground.

9. - Some people thought that it was a coincidence
that the stones looked like the bodies of animals.
- Some triangular shaped stones had been widely
known as tongue stones.
- Nicolas Steno (1638 – 1686), a Danish geologist,
remembered tongue stones when he was
examining the teeth of a shark.
- This led him to believe that tongue stones where
teeth of ancient sharks.

10. - Once scientists had a clear idea that fossils were the remains
of plants and animals that lived in the past, they started to
examine them thoroughly.
- They found out:
a) Some fossils where found in many layers.
b) Some where found in one or few layers.
c) Some where widespread
d) Others found in only few places.
e) Some where easy to recognise.
f) While others needed close and thorough examination to
identify them.

11. - Geologists discovered that some fossils were just found in
just one layer (organism lived in one time period)
- Some fossils were found in many parts of the world and they
were easy to recognise (useful in indicating the age of the
rock). They are known as indicator or index fossils.
- Index fossils are useful where sedimentary rocks have
formed in the same time period but in different ways. Ex.
rock formed from mud an rock formed from limestone.

13. The fossil record
- Each group of living things has a fossil record
(shows when the members of the group existed).
- Some living things like algae and bacteria have a
long fossil record (found in rocks from
Precambrian onwards).
- The mammal group has a much shorter fossil
record (found in Jurassic period onwards)

15. The fossil record and the age of the earth
- Fossils found in a particular layer
can be used to find out about the
conditions on Earth at that time.
- Example 1:
Fossils of plants and animals in
Carboniferous times are of living
things that lived in damp conditions
(shows that may areas where
swamps)

16. - Example 2:
Fossils of living things in Permian
times show that there where deserts.

17. - Fossils show that the features of some living
things has changed over time.
- Scientists think that a change in feature happens
in one individual in a species and then passed on
to the following generations.
- In some circumstances the individual with the
new feature forms a new species . Over a long
period of time the new species might replace the
old species (becomes extinct). This process of
species change is called evolution.

19. - The fossil record does not give a time
when scientists think the Earth formed
but it does suggest that the Earth is very
old.

20. Finding the age of rocks
By using:
Varves Radioactive
materials

21. Finding the age of rocks
- 1st method used to tell the actual age of
rocks by (Gerard De Geer 1858 –
1943):
- He studied the building up sediments in
lakes that received water from melting
glaciers.
- The glaciers have a period of melting every
year during the summer months, and the
water from them carries sand and silt down
the streams into rivers and lakes.

22. - In winter water slows down and
carries only clay particles which
settle over the sand and silt
layer. Together the two bands
count as a year.

23. Radioactive
materials