Sea Floor Spreading Lab ES2 # 1 Purpose: Show rock age and magnetism patterns in spreading sea floor with a paper model.

Transcription

1 Names & B Date your name (first and last) partner Sea Floor Spreading Lab ES2 # 1 Purpose: Show rock age and magnetism patterns in spreading sea floor with a paper model. Background: In the last few decades, scientists have discovered both age and magnetic patterns in the seafloor, which are evidence for plate tectonics. These patterns show that new seafloor has been forming for millions of years at mid-ocean ridges throughout the oceans. Magma melted within the crust rises to the seafloor, cools and solidifies into new rock. In some places this new seafloor is spli t by movement of the asthenosphere under the plates, forming two ocean crust which moves slowly from the ridge. Geologists call this seafloor spreading. Elsewhere, one plate slides under another, or subducts, and deep ocean trenches are formed. Rock on the subducting plate becomes part of the asthenosphere. Oceanic crust is denser and thinner than continental crust, so all seafloor rock is eventually destroyed in this way. Thus, the oldest seafloor rocks are only 180 million years old, but the oldest continental rocks, which cannot be pulled into the trenches, are as old as 4,000 million years, or 4 billion years. Pre-lab thinking. Read the Background above 1. What pulls the new seafloor apart in opposite directions? 2. Where are trenches formed? 3. How old is the oldest seafloor? the oldest continental rocks? Why are the continental rocks so old? Procedure: Look at the diagram on p. 131 in text to see the model. Pull off pages 4 & 5 of your packet.. The black and colored stripes represent north and south paleomagnetism frozen into lava as it leaves the mid-ocean ridge during sea floor spreading. The different colors represent rock ages. 1. Cut the color strip from p. 5 lengthwise and tape the orange ends together. Label the black stripes north and the colored stripes south (If no color printer, color the 4 sections of the rectangle as labeled, and put your name on the strips. Color lightly, and don t take too long, it needn t be perfect. Tape the orange ends together and label stripes as above. 2. Fold pg. 4 lengthwise. Cut slits A, B & C in the center, but not out to the edges. Flatten the paper 3. Put the start ends of the colored strip together, and pull them up through center slit B, like lava erupting from the mid-ocean ridge. Pull the sides, like new sea floor, towards slits A and C. Insert the ends in slits A and C like oceanic crust subducting at a deep ocean trench. Practice moving the strips until you can make the two ends of the strip come up through B and subduct at A and C at the same speed. Analyse 1. Is the rock represented by the orange strip the oldest or youngest? MU (only do if incorrect on or missed original question) Explain how you know: 2. Is the mid-oceanic ridge at SLIT B or SLITS A& C? Circle one: At this boundary are plates coming together or pulling apart? Is this called converging or diverging? MU Explain how ridge is formed: Pg. 1 of 5 ES2 Sea Floor Spreading from Project Earth Science Sanders-Fleming 3/19/09 1:20 PM

2 3. Is the rock represented by the blue strip the oldest or youngest? MU Explain how you know: 4. Is the subduction zone with ocean trenches at SLIT B or SLITS A& C? Are the plates at this boundary converging or diverging? MU Explain how trench is formed: 5. New seafloor rock is continually being formed at mid-ocean ridges and destroyed at trenches in subduction zones. Rock is formed on the continents, but then pushed up into mountains. Which rock will be older, continental or ocean floor? MU Explain why: 6. Ocean plates slide under continental plates. Which are denser, oceans or continents? Which are thicker?? MU Give average thickness of each with measurement unit (use textbook if needed): 7. Pick a color for convergent boundaries and use it on the symbol on the map key at the bottom of page 3. Color all convergent boundaries that color on the map. Are the plates coming together, spreading apart or sliding by each other? Look at the diagram on p of these features are formed at convergent boundaries. Circle them: volcanic islands trench mid-ocean ridge new sea floor volcanic mountain chain rift valley non-volcanic mountain range MU Explain how two are formed--7a: MU Explain how two are formed--7b: 8. Repeat step 7 for divergent boundaries. Are the plates coming together, spreading apart or sliding by each other? 3 of these features are formed at divergent boundaries. Circle them: volcanic islands trench mid-ocean ridge new sea floor volcanic mountain chain rift valley non-volcanic mountain range MU Explain how two are formed--8a: MU Explain how two are formed--8b: 9. On the map, color the transform boundaries a third color and mark it on the map key. Are the plates coming together, spreading apart or sliding by each other? Earthquakes happen at transform boundaries. At what other boundary types do they occur? & MU Explain cause of earthquakes--see text and notes Look at diagram 24 on p. 134, and read the paragraph on transform boundaries. What is caused by the plates rubbing together? 10. What kind of mountains are formed when from the magma when 2 pieces of ocean crust separate, volcanic, or non-volcanic? MU Explain why: Label the Mid-Atlantic Ridge, and Iceland on your map. What kind of boundary is this, divergent or convergent? MU Explain how you know 11. Why are the magnetic stripes on the ocean floor the same on either side of the mid-ocean ridge? (see p. 126) Pg. 2 of 5 ES2 Sea Floor Spreading from Project Earth Science Sanders-Fleming 3/19/09 1:20 PM

3 Give a new fact you learned, or question you still have about seafloor spreading: Name Key: don t color complex or uncertain boundaries Connect boundaries where possible. Compare to map on p. 133 Key: color divergent, convergent, and transform each a different color, here and on map Pg. 3 of 5 ES2 Sea Floor Spreading from Project Earth Science Sanders-Fleming 3/19/09 1:20 PM

4 continent Names & slit A fold along line slit B slit C continent Pg. 4 of 5 ES2 Sea Floor Spreading from Project Earth Science Sanders-Fleming 3/19/09 1:20 PM

5 start start Name blue blue green green yellow yellow orange orange Pg. 5 of 5 ES2 Sea Floor Spreading from Project Earth Science Sanders-Fleming 3/19/09 1:20 PM