Transcript Document
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 Lesson 2: Ancient Earth Earth’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. Lesson 2: Ancient Earth Earth’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. Lesson 2: Ancient Earth POP QUIZ 1. How could studying asteroids and comets help scientists to understand how the solar system formed? 2. Describe the sequence of events in which the solar system formed. 3. What is a nebula? 4. What effect did gravity have on Earth’s formation? 5. What was one source od thermal energy of early Earth? Lesson 2: Ancient Earth The 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) Lesson 2: Ancient Earth The 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. Lesson 2: Ancient Earth POP QUIZ 1. How did gravity affect Earth after its formation? 2. Why isn’t the earliest crust formed present on Earth today? 3. If small islands of solid rock had formed, why would they have not survived for long? 4. Do you think that the same amount of volcanic gases are produced by volcanoes today as they were during the Hadean eon? 5. How did Earth’s early atmosphere form? Lesson 2: Ancient Earth The 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. Lesson 2: Ancient Earth The 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. Lesson 2: Ancient Earth The 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. Lesson 2: Ancient Earth POP QUIZ 1. What are convection currents? How do they form? 2. Would the rate of formation of oceanic crust have been different from its present rate during the Archean eon? 3. What are protocontinents? 4. What are stromalites? Why are stromatolite fossils so rare? 5. What conditions made early Earth able to support life? 6. How did Earth’s oceans form? 7. Why did the rain during the Archean eon dissolve rocks more rapidly than it does today? Lesson 2: Ancient Earth The 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. Lesson 2: Ancient Earth POP QUIZ 1. How were the convection currents in the mantle affected by the overall change in Earth’s temperature during the Proterozoic eon? 2. How long did the Proterozoic eon last? 3. What geologic evidence of the hypothesized Snowball Earth period would you expect to find in the fossil record? 4. How did changes in Earth’s environment affect the evolution of life? 5. What happened during the Great Oxygenation Event? Lesson 2: Ancient Earth The 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 Lesson 2: Ancient Earth POP QUIZ 1. Why do you think it took millions of years for a supercontinent such as Rodinia to form? 2. What caused the continents to collide and stick together? 3. What supercontinent existed before Pangea? 4. What was the dominant type of life during the Proterozoic eon? 5. What important evolutionary change occurred at the end of the Proterozoic eon? 6. Why were unicellular organisms dominant during this eon, even though multicellular organisms also evolved during this time? Lesson 2 Review Time • Do the Lesson 2 review (p. 94) in your notebooks… • We’ll review in 15 minutes.