1. History of Life on Earth
The Evolution of Earth
History of Life on Earth

2. A. Lesson One Introduction to Earth
Take out a piece of binder paper and fold it in half (hotdog) to make two columns
Label the left column observations and the right column questions
Label page 1 in the top left hand corner

3. I. Our Blue Orb: How did it evolve?
A. Using this image and the globe, list as many observations as you can about the Earth in one column. In the other, list as many questions that come to your mind as you can.

4. Questions about Origins
B. Where do you think the Earth came from? Explain or draw your idea on a board, and on the back of your binder paper title A. Lesson One Introduction to Earth. Label as page 2.
C. Scientists have been able to figure out how old the Earth is, based on rocks and meteors. They believe it is about 4.5 Billion years ago. Do you think the Earth looked then the way it does now? Explain or draw your idea on a board and on the bottom of page 2.

5. The Atmosphere D. Copy the chart onto a new piece of paper labeled page 3 and titled D. The Atmosphere.
Place a piece of plastic wrap around your globe: this simulates the depth of the atmosphere

6. D. Atmosphere cont.
Add any other observations or questions about our atmosphere to your columns in part A (page 1).
Do you think there was an atmosphere at the beginning of Earth? Why or why not? How do you think it got to be there? Answer on page 3 below chart.

7. *

8. E. Land Google Earth View
What observations can you make about the features on land? Study the image on screen, and the images presented on Google Earth. What other observations about the features on land can you make? Add those to your columns in part A. Do you think these features were part of the original Earth? Why or why not? Answer these question on page 3 Title E. Land.

9. The Age of the Earth Earth is ~ 4,570,000,000 years old
Meteorites give us access to debris left over from the formation of the solar system
We can date meteorites using radioactive isotopes and their decay products *

10. II. Evolving Atmosphere
A. Put the saran wrap around your globe again.
If this really were the atmosphere, would it have been there to start? What kinds of gases do you think would have originally been near the surface of the Earth? What would have happened to them? What keeps gases in place around a planet? Respond on the back of page 3. Label it page 4. Title II Evolving Atmosphere.
B. Where could other gases have come from that would make an atmosphere?
C. What kinds of gases would have originally gathered?
D. What do you think would have ultimately created the Oxygen rich atmosphere we have now?

11. The Evolving Atmosphere
Right after its creation, the Earth is thought to have had a thin atmosphere composed primarily of helium (He) and hydrogen (H) gases
The Earths gravity could not hold these light gases and they easily escaped into outer space
Today, H and He are very rare in our atmosphere *

12. The Evolving Atmosphere
For the next several hundred million years, volcanic out-gassing began to create a thicker atmosphere composed of a wide variety of gases
The gases that were released were probably similar to those created by modern volcanic eruptions *

13. The Evolving Atmosphere
These would include:
Water vapor (H2O)
Sulfur dioxide (SO2)
Hydrogen sulfide (H2S)
Carbon dioxide (CO2)
Carbon Monoxide (CO)
Ammonia (NH3)
Methane (CH4)
Note that oxygen (O2) gas is not created by volcanic eruptions *

14. III. Earth’s Oceans Emerge
A. Consider a flat surface that represents the Earth. Consider the initial temperature and conditions of that Earth.
B. Then, pour a little bit of water into the tin, and consider how water might have gotten there
C. Record your ideas on a new piece of binder paper. Label page 5 and title III Earth’s Oceans Emerge.

15. Creating the Oceans
It is hypothesized that water vapor escaping from the interior of the Earth via countless volcanic eruptions created the oceans (this took hundreds of millions of years) *

16. Creating the Oceans
Astronomers also hypothesize that comets impacting the Earth were a major source of water that contributed to creation of the oceans
Remember, that comets are best described as “dirty ice balls” *

17. Creating the Oceans
The earliest evidence of surface water on Earth dates back about 3.8 billion years *

18. A billion Year Old Earth
By 3.5 billion years ago, when the Earth was a billion years old, it had a thick atmosphere composed of CO2, methane, water vapor and other volcanic gases
By human standards this early atmosphere was very poisonous
It contained almost no oxygen
Remember, today our atmosphere is 21% oxygen *

19. A billion Year Old Earth
By 3.5 billion years ago, the Earth also had extensive oceans and seas of salt water, which contained many dissolved elements, such as iron *

20. The Creation Of Life
These 3.5 billion year old fossilized algae mats, which are called stromatolites, are considered to be the earliest known life on earth
They are found in Western Australia *

21. Evidence of surface water 4 Billion yrs ago
Isotope of oxygen found in surface water found in zircon crystals in Australia and the Arctic

22. Oxygen
The ability of cyanobacteria to perform oxygenic photosynthesis is thought to have converted the early Earth atmosphere into an oxidizing one, which dramatically changed the life forms on Earth and provoked an explosion of biodiversity *

23. Oxygen
By around 2.2 to 2.4 billion years ago, the Earth had developed an atmosphere that is very similar to today’s atmosphere (nitrogen and oxygen) *

24. Banded Iron Formations
How do we know that there was no oxygen in the early Earth atmosphere?
Simply put, water and oxygen creates rusts out of iron *

25. Banded Iron Formations
BIFs are primarily found in very old sedimentary rocks, ranging from over 3 to 1.8 billion years in age *

26. The Continents
By 2.5 billion years ago, the continents had been formed
The density of the continental crust (2.8 gr/cm3) is lighter that the crust found on ocean bottoms (3.2 gr/cm3), so the continents rise above the ocean floor
A question that remains unanswered is, when did plate tectonics start? *

27. The Oldest Continents