4-Jan 30 - NATS Announcements Past date for Bio Sketch...

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1 NATS Announcements: 1/30/08 Past date for Bio Sketch credit; please complete anyway so we can get to know you Extra credit this evening at 7pm; see announcement on ARIS Bring your textbook to each discussion section (Th, F) Lots of useful info at http://nats101.geo.arizona.edu/ My office hours: T 1:30-2:30 and Th 2:30-3:30 and by appointment (Gould-Simpson 334; [email protected]) Please put “NATS” in subject line of email and always give your name and section number Please remember that this course has 3 main components: lectures, textbook, and discussion sections. To do well on exams, quizzes, assignments, you need to use all 3 components… (plus think, ask questions…) Evidence from the Seafloor Additional observations about the magnetic properties of seafloor rocks supported the seafloor spreading hypothesis Earth has a magnetic field because it has: 1. Molten rock in the outer core 2. Heat to generate currents in outer core 3. Rotation to mix the currents Evidence from the Seafloor • Atoms in magnetic minerals align parallel to the magnetic field when magma cools to form seafloor rocks ! Preserves ancient magnetic field – paleomagnetism ! Analysis reveals the inclination of the field where they formed – a proxy for latitude Inclination : parallel to flux lines: • Horizontal at equator • Vertical at pole The Good Earth/Chapter 4: Plate Tectonics ! Each period of normal or reversed polarity averages 250,000 years ! Longest = 10’s of millions of years ! Shortest = 10’s of thousands of years ! Few thousand years to change polarity (normal ! reverse or reverse ! normal) Magnetic Field Reversals Normal polarity (a) when negative magnetic pole is near geographic North Pole (current status) Reverse polarity (b) when positive magnetic pole is near geographic North Pole Evidence from the Seafloor The Good Earth/Chapter 4: Plate Tectonics • Normal polarity rocks currently forming from magma along oceanic ridge ! Marine surveys measure strength of Earth’s magnetic field ! Strength higher in regions of normal polarity, lower where there is reverse polarity Evidence from the Seafloor The Good Earth/Chapter 4: Plate Tectonics • Polarity of seafloor alternates between normal (+) and reverse (-) on either side of oceanic ridge ! Symmetrical pattern on either side of ridge ! “stripes” of similar width and polarity
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2 Evidence from the Seafloor
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4-Jan 30 - NATS Announcements Past date for Bio Sketch...

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