Origins of life on earth

1. Origins of life on earth Key words: fossils, evidence

2. Explain these pictures What link can you make between rocks and fossils?

3. Objective • What are the origins of life on earth? • Success Criteria • By the end of the lesson I: • can explain what a fossil is and what we can learn from them. • can explain how the layers of the earth help to identify the time in which some organisms lived and died • can identify how fossils help us to understand ehat animals were like and how they lived

4. What do we know? Its believed the earth is about 4500 million years old and that life began about 3500 million years ago. A termite found to be 100 million years old There is some debate as to whether the first life developed due to the conditions on earth, or whether simple life forms arrived from another planet. A plesiosaur shark 350 million years ago

5. What are fossils? The rocks are formed from sediments and many contain fossils. Fossils are formed when the harder parts of the organism are replaced by minerals from rocks over long periods of time. In other cases, the remains have been completely dissolved and what is left is an impression, which may later fill with minerals to produce a cast of the organism. In very rare situations, organisms do not decay after death due to temperatures being too low. These fossils are preserved in ice.

6. Fossilization

7. A rare event Fossilization is a rare event. Different types of fossil form under different conditions and environments. mud amber ice and frozen soil Fossilized remains only form in the absence of microbes, which need food, oxygen, water and warmth. What type of fossil forms whether there are microbes present or not? ash/mud

8. What does the fossil record show? The history of life on Earth as shown by fossils is called the fossil record. • SUCCESS CRITERIA: • I can; • Explain what a fossils is and what • we can gain from them • can explain how the layers of the • earth help to identify the time in • which some organisms lived and died Although there are gaps in the fossil record, it helps to tell the evolutionary story of past and present-day organisms. It can showhow the changes in an organism were linked to changes in its habitat. The fossil record can also show how different species evolved from common ancestors.

9. Layers of evidence Why is the fossil record not complete? Fossils are found in rocks that wear away, get buried or melted (rock cycle). Sometimes some bits of a fossil is recovered rather than everything. We do however have a complete record of some animals… Scientists believe that 4 billion species of plants and animals have lived during the history of earth. Some have disappeared completely whilst others have living relatives.

10. Gradual changes in fossil records

11. Theory Summary Theories about the dawn of life There are many theories of how life first appeared on Earth, but no-one is sure which one is correct. This is because direct evidence from 4 billion years ago is scarce as a result of constant transformation of the Earth’s surface. There are three general types of theory: prebiotic broth proteins developed from a cold broth of molecules hydrothermal metabolites formed in hot, high-pressure, low-oxygen environments extra-terrestrial life arrived on Earth on meteorites

12. plenary Summary

13. Objective • What are the origins of life on earth? • Success Criteria • By the end of the lesson I: • can explain what a fossil is and what we can learn from them. • can explain how the layers of the earth help to identify the time in which some organisms lived and died • can identify how fossils help us to understand ehat animals were like and how they lived