Monday Warm-Up

1. Monday Warm-Up • Create vocab cards/flaps/whatever you like for Chapter 3, lesson 2 words: • Hadean eon • Archean eon • Protocontinent • Proterozoic eon • The Great Oxygenation Event/Oxygen Catastrophe

2. Lesson 2: Ancient EarthEarth’s Earliest History • Scientists hypothesize that the solar system formed when a nebula was pulled together by gravity. • Gravity pulled the particles of the nebula together. • The particles formed a flat, rotating disk. • Material in the center of the disk formed the Sun.

3. Lesson 2: Ancient EarthEarth’s Earliest History • Remaining particles of the disk attracted each other, forming the planets. • Collisions of particles produced thermal energy. • The hot, soft materials of ancient Earth flowed into the shape of a sphere. • Asteroids crashed into Earth, making Earth even hotter.

4. Lesson 2: Ancient EarthPOP QUIZ • How could studying asteroids and comets help scientists to understand how the solar system formed? • Describe the sequence of events in which the solar system formed. • What is a nebula? • What effect did gravity have on Earth’s formation? • What was one source od thermal energy of early Earth?

5. Lesson 2: Ancient EarthThe Hadean Eon • The first 640 million years of Earth history are called the Hadean eon. • Earth was much hotter during the Hadean eon. Scientists think that molten rock covered Earth’s surface. • Collisions with asteroids and radioactive decay produced huge amounts of thermal energy. • Eventually, fewer and fewer asteroids struck Earth. (cooling) • The radioactive elements on Earth decayed and formed stable daughter elements, so less radioactive material was present. (cooling)

6. Lesson 2: Ancient EarthThe Hadean Eon • Small islands of solid rock may have started floating on Earth’s surface… but the motion of the molten seas or asteroid impacts would have melted them… until… • As Earth cooled, the molten surface solidified to form an ancient crust. • Poisonous volcanic gases formed Earth’s earliest atmosphere when they escaped from inside Earth.

7. Lesson 2: Ancient EarthPOP QUIZ • How did gravity affect Earth after its formation? • Why isn’t the earliest crust formed present on Earth today? • If small islands of solid rock had formed, why would they have not survived for long? • Do you think that the same amount of volcanic gases are produced by volcanoes today as they were during the Hadean eon? • How did Earth’s early atmosphere form?

8. Lesson 2: Ancient EarthThe Archean Eon • During the Archean eon (the period of time that occurred from about 4 to 2.5 billion years ago), Earth had its first solid surface. • Earth was cooler during the Archean eon, but still produced twice as much thermal energy as present Earth. • The oldest rocks discovered are from this eon. • Extensive volcanic activity formed Earth’s first oceanic crust through convection currents. • The first, small continents were the protocontinents.

10. Lesson 2: Ancient EarthThe Archean Eon • During the Archean eon, the temperature in Earth’s atmosphere dropped, causing the water vapor in the air to condense. • The water, which was made acidic by gases in the air, fell as rain. • By the time the low areas of the oceanic crust filled with water, the new oceans were salty.

11. Lesson 2: Ancient EarthThe Archean Eon • Fossil remains of unicellular bacteria and cyanobacteria are the earliest evidence of life that formed in the warm Archean oceans. • Sometimes sticky strands of cyanobacteria trap sediment from the ocean and form visible mounds called stromatolites.

12. Lesson 2: Ancient EarthPOP QUIZ • What are convection currents? How do they form? • Would the rate of formation of oceanic crust have been different from its present rate during the Archean eon? • What are protocontinents? • What are stromalites? Why are stromatolite fossils so rare? • What conditions made early Earth able to support life? • How did Earth’s oceans form? • Why did the rain during the Archean eon dissolve rocks more rapidly than it does today?

13. Lesson 2: Ancient EarthThe Proterozoic Eon • The time after the Archean eon is known as the Proterozoic eon. • During the Proterozoic eon, oxygen was added to the atmosphere. • During the Great Oxygenation Event, or Oxygen Catastrophe, atmospheric oxygen increased from about 3% to 20%. • The oxygen-rich atmosphere harmed organisms adapted to the earlier lower oxygen levels. • The Snowball Earth hypothesis states that Earth was completely covered with ice at the end of the Proterozoic eon.

15. Lesson 2: Ancient EarthPOP QUIZ • How were the convection currents in the mantle affected by the overall change in Earth’s temperature during the Proterozoic eon? • How long did the Proterozoic eon last? • What geologic evidence of the hypothesized Snowball Earth period would you expect to find in the fossil record? • How did changes in Earth’s environment affect the evolution of life? • What happened during the Great Oxygenation Event?

16. Lesson 2: Ancient EarthThe Proterozoic Eon • Scientists hypothesize that the supercontinent Rodinia formed during the Proterozoic eon, before Pangea. • Rodinia might have formed as separate continents collided and stuck together. • The first multicellular organisms evolved in the oceans at the end of the Proterozoic eon

17. Lesson 2: Ancient EarthPOP QUIZ • Why do you think it took millions of years for a supercontinent such as Rodinia to form? • What caused the continents to collide and stick together? • What supercontinent existed before Pangea? • What was the dominant type of life during the Proterozoic eon? • What important evolutionary change occurred at the end of the Proterozoic eon? • Why were unicellular organisms dominant during this eon, even though multicellular organisms also evolved during this time?

18. Lesson 2 Review Time • Do the Lesson 2 review (p. 94) in your notebooks… • We’ll review in 15 minutes.

19. B E L L W O R K Make sure this goes in your NB