1. Warmup 10/19/15 How do you think scientists work to find out how old the Earth is? What kind of evidence and stuff do you think they look for? Objective Tonight’s Homework To learn about the different ideas on Earth’s history Read 5.1 to 5.3 Research a geologic period

2. Research a Geologic Period Part of your homework for the first part of this week is to do a little research on one of the geologic periods secular scientists believe occurred in the past and make it into a small poster on a piece of construction paper by Thursday. For your geologic period, you need to find the following information: - Earth’s temperature (like 3 degrees hotter than now) - How much oxygen was in the atmosphere (like 30%) - A map showing roughly what the Earth would have looked like - What sort of life inhabited the land and oceans - When this geological period started and ended - 2 other facts or interesting things

3. Protozeroic

4. Precambrian

5. Cambrian

6. Ordovician

7. Silurian

8. Devonian

9. Carboniferous

10. Permian

11. Triassic

12. Jurassic

13. Cretaceous

14. Paleocene

15. Earth’s Origin Secular scientists say the Earth is about 4.5 billion years old. How did they get to this number? How much of this 4 billion years is filled in?

16. Earth’s Origin Scientists get this number by looking at rocks and doing something called “radiometric dating”. It’s complex, but some kinds of atoms can change into other kinds after a rock has stopped being molten. This is a slow process. We think it takes billions of years. So scientists get the age of a rock by seeing how much of it has changed from one kind of atom into another.

17. Earth’s Origin How do scientists use this? When they look at rocks, scientists have noticed that many of them run in layers – or strata. When they radiometric dating to find out the ages of these rocks, they generally find that the ones on bottom are older. Because of this, most scientists estimate the age of a fossil depending on what layer it was found in.

18. Earth’s Origin Shortly after the Earth formed, scientists think a smaller planet smashed into it at an angle. What’s the evidence for this? When we look at moon rocks, we find that they’re made of the same kind of rock as the surface of the Earth. Plus, the moon seems to have a smaller iron core than it should.

19. Earth’s Origin The idea is that when this other planet smashed into the Earth, a lot of the light, surface rocks went into space, clumped together, and made the moon. While the heavier stuff like iron all stayed on Earth and sank down to the core.

20. Earth’s Origin Scientists also say the earliest life formed 3.5 billion years ago. Where do they get this number? The picture below shows a fossil of something called a “microbial mat”. This is essentially bacteria that has fossilized. Since these rocks have been dated to be 3.5 billion years old, the fossils in them must be that old, too.

21. Earth’s Origin By this point, evidence suggests that the Earth already had seas and rivers. They also believe that the atmosphere had almost no oxygen. You and I would find it very hard to survive here! The water for the seas and oceans is believed to have come mostly from comets hitting the early Earth. Comets are made mostly of ice and snow so this could work. Although recent evidence is starting to show some serious problems here, so scientists don’t have a good answer right now for why Earth has so much water.

22. Earth’s Origin 500 million years ago, life went very suddenly from being simple cells to being tons of complex creatures that are the ancestors to all the different kinds of creatures today. This was called the Cambrian Explosion. Scientists know this happened because a ton of new species appeared all at once in the fossil record. Only at this point did Earth get a lot of oxygen.

23. Earth’s Origin 400 million years ago, the first creatures to live on land started to appear. This wouldn’t have been complex animals yet, but rather simple things like fungus and algae. Things like land animals and plants didn’t evolve until much later.

24. Earth’s Origin Around 200 million years ago, plate tectonics had moved all the continents into one giant landmass called “Pangaea”. A lot of the early dinosaurs existed around this time. Note that things like grass and flowers didn’t exist yet.

25. Earth’s Origin Only 6 million years ago, we get the earliest human ancestors. While they look a lot like monkeys, scientists explain that these early “hominids” were different. There were tons of hominids that became increasingly more human-like the closer we get to the present. Actual civilization began around 7,000 B.C.

26. Earth’s Origin Most scientists believe that Earth went through several ice ages in the last 500,000 years or so. How do they know this? By taking deep ice core samples. Dust and things get trapped in ice. As ice builds up layer by layer, it makes strata like rocks. If scientists drill out a cylinder of ice, they can study this dust to learn about things like temperature and atmosphere from the past.

27. Earth’s Origin This seems like a pretty complete and detailed history, right? Scientists have spent a lot of time and effort to put this history together from the pieces we see from fossils, rocks, and other data. As Christians, we often feel a lot of pressure to accept these scientific theories. After all, this is so detailed… how could it be wrong? But it’s important to remember that humans have made tons of theories before that were super complex and detailed, but turned out to be wrong.

28. Exit Question What do scientists call the name of the supercontinent that supposedly existed in the time of the dinosaurs? Mega Land Supercontinent Pangaea America Dinotopia None of the above