1. Bellwork: In what ways has the Earth changed through time
Bellwork: In what ways has the Earth changed through time? How do we know and gather information about these changes ?

2. Section 19.1: The fossil record
The history of Life
Section 19.1: The fossil record

3. Fossils and Ancient Life
Fossils provide information about extinct species
Fossils can vary greatly
Different sizes, types and degrees of preservation
Not every organism will become a fossil

4. Types of Fossils

5. Trace Fossils

6. Fossils in Sedimentary rocks
Why don’t all organisms become fossils?

7. What information can fossils tell you?
The structure of an organism
Lead to ideas about evolutionary relationships
The Environment an Organisms lived in
Fossilized plants and leaves give an idea of the ecosystem
The way in which an organism lived
Footprints and bone structure give information about how an animal moved
Groups of fossils give information about how organisms interacted

8. How do researchers know the age of fossil specimens?
Two types of dating
Relative dating
Radiometric dating
Relative dating used the presence of an index fossil or other feature to determine whether a rock is older or younger than another rock
Can allow paleontologists to tell the age of a rock

9. What is an index fossil?
Index fossils are fossils used to establish the relative age of a rock layer
Often distinctive
Found in many places
Only existed on Earth for a small amount of time
Trilobites are a great example
15,000 different species
Can be used to date nearly 300 million years worth of rocks

10. What is radiometric dating?
Radiometric dating uses the proportion of radioactive to stable isotopes to calculate the age of a sample
Different elements decay at different rates
The rate of decay is referred to as the half life
Carbon 14 decays to Carbon 12 naturally in the atmosphere
When a plant photosynthesizes it will take in a small amount of Carbon 14
Upon death, this amount of carbon is fixed – and will decay over time to carbon 12
Carbon 14 will not be replenished, so by measuring the amount of carbon 14 remaining, the age of the plant can be calculated
Animals also get carbon from eating plants so can be dated this way
Half life of carbon is 5730 years

11. How do you date samples older than 60,000 years?
Carbon-14 is not the only isotope used for radiometric dating
Elements such as Rubidium (half life 48.8 billion years), Uranium (half life 4.5 billion years).
By choosing the correct element you can essentially date anything on Earth
These are often used alongside index fossils to determine the ages of geological units

12. Why don’t we just radiometrically date everything?
Because it is very expensive and takes a very long time!

13. How old is the Earth? 4.6 billion years old
Divided into Eons, Eras, Periods and Epochs
Precambrian is the first 3.5 billion years
Our Geological period only started 1.8 million years ago

14. Geological time as a clock
It is often hard to comprehend simply how old the Earth is, and for how little humans have occupied it
This graphic puts it into perspective

15. How has the Earth changed through geological time?

16. What has affected conditions on Earth through time?
Physical Forces
Climate is constantly changing
Great ice age 10,000 years ago, average temperature was only 5 Celsius lower,
During the Mesozoic, average temperatures were only 6 – 12 Celsius higher
Earth is constantly changing – Mountains, Volcanoes, New Coastlines, which has knock on effects to habitats
Plate Tectonics and Super- continental Cycles are a powerful driving force

17. Biological effects on Earth through time
Life can have a large affect in shaping Earth
Early Oceans were full of dissolved Iron
Atmosphere did not have much Oxygen
Some of the first organisms to Evolve were photosynthetic bacteria
These took in CO2 and gave out O2
CO2 is a greenhouse gas – the reduction in CO2 levels lead to drops in global temperatures
As temperatures dropped, Iron reacted with atmospheric oxygen, was no longer soluble in the oceans and precipitated out
This settled to the ocean floor – producing banded Iron formations

18. Key points
Fossils are a powerful tool used to aid our understanding of the evolution of the Earth
They can be dated through either relative or radiometric dating
Earth is 4.6 billion years old
The Earth’s surface has been shaped a number of different physical and biological factors over the course of it’s history