1. Change Through Time
Unit 4

2. Objectives
I can…
Explain how inherited traits in a population can lead to biological diversity
Explain how evolution may result from the process of natural selection
Explain evidence that supports the change in genetic composition of a population over successive generations

3. Warm Up Question
If you could travel in time, what are 2 things you would do? You may not commit murder or steal anything.

4. Chapter 17: The History of Life

5. 17.1 The Record of Life
The Earth is currently estimated to have formed approximately 4.6 BYA
Sun- 4.6 BYA
Moon- 4.5 BYA
How do scientists measure this?
Relative Dating- As each layer of sediment is added, it is newer (younger) than the rock that is below it. This does not give us an exact amount of time, it only tells us which layers are older and which layers are younger.

6. 17.1 The Record of Life
Radiometric Dating- As atoms age they give off radiation in the form of neutrons. They do this at a steady rate, therefore, as long as scientists know the half life, or the amount of time an element loses half of its neutrons, then they can use that to measure the approximate age of the sediment around it.

7. 17.1 The Record of Life Early Earth was entirely inhospitable
4.6 BYA- Hot ball of rock bombarded by meteorites
3.9 BYA- Earth cooled down and water was able to exist as a liquid- enter: OCEANS
Super hot and still inhospitable
3.5 BYA- The first life definitely appeared
Could have been earlier than that, but we don’t have the fossils of the organisms

8. 17.1 The Record of Life
A fossil is any evidence of an organism that lived long ago. Studying fossils and drawing conclusions about them is intense work that requires a vast scope of knowledge about geology, biology, chemistry, and history. The people who do this are called paleontologists.
Fossils are only found in sedimentary rocks and occur under very specific conditions. This causes huge gaps in the fossil record because:
Not all rock is sedimentary
Not all animals die in a pile of mud
Fossils that were once deposited were later exposed to the environment and destroyed by weather

9. 17.1 The Record of Life Types of Fossils
Molds- Empty space left in a rock that is the shape of an organism (Ice Tray)
Casts- When sediment fills a mold and takes on the shape of an organism (Ice)
Amber-preserved and Frozen- An entire intact organism is preserved in a substance that is changing from a liquid to a solid
/in-siberia-a-perfectly-preserved-frozen-cave-lion- cub/
Trace- Fossilized footprint, tail print, burrow, feces, etc.
Petrified- When the atoms that make up an organism (most commonly plants) are replaced by minerals
Imprints- Created by thin objects falling into sediment as it is hardening

10. 17.1 The Record of Life
Geologic Time Scale- Earth’s history has been divided into four (becoming 5) eras. These eras are distinguished by the types of organisms that lived during them.
(January 1st) Precambrian- First Signs of Life Appear
(March 20th) Paleozoic- Vertebrates Appear
(December 20th) Mesozoic- Mammals Appear
(December 26th) Cenozoic- Primates Diversified into Several Large Apes
Anthropocene- The current era, marked by the largest mass extinction event in the history of our planet

11. Early scientists believed in the idea of spontaneous generation
17.2 The Origin of Life
Early scientists believed in the idea of spontaneous generation

12. 17.2 The Origin of Life
Francisco Redi- Italian physician in the 17th century
Disproved spontaneous generation
Louis Pasteur- French scientist that conducted an experiment to support Redi and brought about the concept of biogenesis
Biogenesis- living things come from other living things

13. 17.2 The Origin of Life

14. Biogenesis does not answer the question of where life came from
17.2 The Origin of Life
Biogenesis does not answer the question of where life came from
Two main events must have occurred:
1) Organic molecules had to form, spontaneously
2) These molecules had to be organized into complex organic molecules
Stay tuned….

15. Unit 4 is not complete yet
But this is where we are ending for the second trimester.