Earth Science ocean floor, rock type, Plate tectonics

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ICS 1 Block 2 8/29-9/9

Lesson Day 1: Ocean Floor Characteristics

Standard(s): ES 3. a.

Students know features of the ocean floor (magnetic patterns, age, and sea-floor topography) provide evidence of plate tectonics.

Objective (s): Understand the “zebra pattern” on the ocean floor and how this is evidence for sea-floor spreading

Pace

Warm-up

(10 min)

Notes

(20 min)

Guided

Practice

(20 min)

Critical thinking (5min)

Independent

Practice

(20 min)

Review

(5 min)

Closing

(5 min)

Description of Activity

Sunlight can’t reach the Ocean Floor.

What does the ocean floor look like?

Does life exist? If so, what form is it?

Topic: Ocean Floor skip three between

Topography-

Zebra stripes-

Magnetic field-

Power point

Video: 9 min Sea Floor Spreading with Bill Nye

Explain how sonar helped in the mapping of the Earth’s

Ocean Floor.

What does the Ocean floor look like? Why is it like that?

Reading / Questions: http://pubs.usgs.gov/gip/dynamic/dynamic.html#anchor1

9309449

Handout: Vocab crossword

Summary, graphic organizer

Go over homework

Crossword

Standards

ES 3. Plate tectonics operating over geologic time have changed the patterns of land, sea, and mountains on Earth’s surface.

As the basis for understanding this concept:

ES 3. a. Students know features of the ocean floor (magnetic patterns, age, and sea-floor topography) provide evidence of plate tectonics.

Much of the evidence for continental drift came from the seafloor rather than from the continents themselves. The longest topographic feature in the world is the mid-oceanic ridge system, a chain of volcanoes and rift valleys about 40,000 miles long that rings the planet like the seams of a giant baseball. A portion of this system is the Mid-Atlantic Ridge, which runs parallel to the coasts of Europe and

Africa and of North and South America and is located halfway between them. The ridge system is made from the youngest rock on the ocean floor, and the floor gets progressively older, symmetrically, on both sides of the ridge. No portion of the ocean floor is more than about 200 million years old. Sediment is thin on and near the ridge. Sediment found away from the ridge thickens and contains progressively older fossils, a phenomenon that also occurs symmetrically.

Mapping the magnetic field anywhere across the ridge system produces a striking pattern of high and low fields in almost perfect symmetrical stripes. A brilliant piece of scientific detective work inferred that these “zebra stripes” arose because lava had erupted and cooled, locking into the rocks a residual magnetic field whose direction matched that of Earth’s field when cooling took place. The magnetic field near the rocks is the sum of the residual field and Earth’s present-day field. Near the lavas that cooled during times of normal polarity, the residual field points along Earth’s field; therefore, the total field is high. Near the lavas that cooled during times of reversed polarity, the residual field points counter to Earth’s field; therefore, the total field is low.

The “stripes” provide strong support for the idea of seafloor spreading because the lava in these stripes can be dated independently and because regions of reversed polarity correspond with times of known geomagnetic field reversals. This theory states that new seafloor is created by volcanic eruptions at the mid-oceanic ridge and that this erupted material continuously spreads out convectively and opens and creates the ocean basin. At some continental margins deep ocean trenches mark the places where the oldest ocean floor sinks back into the mantle to complete the convective cycle. Continental drift and seafloor spreading form the modern theory of plate tectonics.

ES 3. b. Students know the principal structures that form at the three different kinds of plate boundaries.

There are three different types of plate boundaries, classified according to their relative motions: divergent boundaries; convergent boundaries; and transform, or parallel slip, boundaries.

Divergent boundaries

occur where plates are spreading apart. Young divergence is characterized by thin or thinning crust and rift valleys; if divergence goes on long enough, mid-ocean ridges eventually develop, such as the Mid-Atlantic Ridge and the East Pacific Rise.

Convergent boundaries

occur where plates are moving toward each other. At a convergent boundary, material that is dense enough, such as oceanic crust, may sink back into the mantle and produce a deep ocean trench. This process is known as

subduction.

The sinking material may partially melt, producing volcanic island arcs, such as the Aleutian Islands and Japan. If the subduction of denser oceanic crust occurs underneath a continent, a volcanic mountain chain, such as the Andes or the Cascades, is formed. When two plates collide and both are too light to subduct, as when one continent crashes into another, the crust is crumpled and uplifted to produce great mountain chains, such as the relatively young Himalayas or the more ancient Appalachians.

The third type of plate boundary, called a

transform,

or

parallel slip, boundary,

comes into existence where two plates move laterally by each other, parallel to the boundary. The San Andreas fault in California is an important example. Marking the boundary between the North American and Pacific plates, the fault runs from the _______Gulf of California northwest to Mendocino County in northern

California.

ES 3. c. Students know how to explain the properties of rocks based on the physical and chemical conditions in which they formed, including plate tectonic processes.

Rocks are classified according to their chemical compositions and textures. The composition reflects the chemical constituents available when the rock was formed. The texture is an indication of the conditions of temperature and pressure under which the rock formed. For example, many igneous rocks, which cooled from molten material, have interlocking crystalline textures. Many sedimentary rocks have fragmental textures. Whether formed from cooling magma, created by deposits of sediment grains in varying sizes, or transformed by heat and pressure, each rock possesses identifying properties that reflect its origin.

Plate tectonic processes directly or indirectly control the distribution of different rock types. Subduction, for example, takes rocks from close to the surface and drags them down to depths where they are subjected to increased pressures and temperatures. Tectonic processes also uplift rocks so that they are exposed to lower temperatures and pressures and to the weathering effects of the atmosphere.

Vocabulary

1.

2.

Sea-floor topography the relief features or surface configuration of an area

Plate tectonics theory in which the lithosphere is divided into pieces, each move on the plastic

3.

4.

asthenosphere to collide with, slide under, or move past adjacent pieces

Continental drift the lateral movement of continents resulting from the motion of crustal plates

Mid-ocean ridge extend through the Atlantic, Indian, and South Pacific oceans: each is hypothesized to

5.

be the locus of seafloor spreading

Rift valleys chasm extending along the crest of a mid-ocean ridge, locus of the magma upwelling that

6.

7.

accompany seafloor spreading

Sediment mineral or organic matter deposited by water, air, or ice

Fossils remains, impression, or trace of a living thing of a former geologic age, as a skeleton, footprint, etc

Magnetic field near a magnet, electric current, or moving charged particle in which a magnetic force acts 8.

on any other magnet, electric current, or moving charged particle

9.

Zebra stripes pattern created by the changing Earth’s magnetic field on the ocean crust

10.

Polarity the property or characteristic that produces unequal physical effects at different points in a magnet or storage battery

11.

Lava the molten, fluid rock that issues from a volcano or volcanic vent

12.

Seafloor spreading process in which new ocean floor is created as molten material from the earth's mantle rises in margins between plates or ridges and spreads out

13.

Ocean Basin a large geologic areas that are below sea level

14.

Deep Ocean trench any long, narrow, steep-sided depression in the ocean bottom in which maximum oceanic depths (24,000–36,000 ft)

15.

Convection cell a volume of circulating material, under gravity, that is heated from below and cooled from above

16.

Divergent boundary type of tectonic boundary where two plates are moving in the opposite direction.

17.

Convergent boundary type of tectonic boundary where two plates are moving toward each other

18.

Transform boundary type of tectonic boundary where two plates are moving past each other in opposite directions

19.

Oceanic crust part of Earth's lithosphere that covers the ocean basins

20.

Continental Crust the layer of igneous, sedimentary, and metamorphic rocks which form the continents

21.

Mantle is a highly viscous layer between the crust and the outer core

22.

Subduction one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge

23.

Volcanic island arcs generally they result from the subduction of an oceanic tectonic plate under another tectonic plate, and often parallel an oceanic trench

24.

Volcanic mountain chain when oceanic crust subducts beneath continental crust on an adjacent plate, creating an arc-shaped mountain belt

25.

San Andreas Fault continental transform fault that runs a length of roughly 810 miles (1,300 km) through California

26.

Chemical composition is the simplest whole number ratio of atoms of each element present in a compound.

27.

Igneous rock formed through the cooling and solidification of magma or lava

28.

Crystalline texture the distribution of crystallographic orientations of a polycrystalline sample

29.

Sedimentary rock minerals and/or organic particles settle and accumulate to form a new material

30.

Metamorphic rock the transformation of an existing rock type to a new rock type through heat and/or pressure

Earth Science ocean floor, rock type, Plate tectonics

Across

3. the transformation of an existing rock type to a new rock type through heat and/or pressure

5. a volume of circulating material, under gravity, that is heated from below and cooled from above

7. formed through the cooling and solidification of magma or lava

8. the molten, fluid rock that issues from a volcano or volcanic vent

9. remains, impression, or trace of a living thing of a former geologic age, as a skeleton, footprint, etc

10. pattern created by the changing Earth’s magnetic field on the ocean crust

15. the lateral movement of continents resulting from the motion of crustal plates

21. type of tectonic boundary where two plates are moving toward each other

22. when oceanic crust subducts beneath continental crust on an adjacent plate, creating an arc-shaped mountain belt

23. process in which new ocean floor is created as molten material from the earth's mantle rises in margins between plates or ridges and spreads out

24. generally they result from the subduction of an oceanic tectonic plate under another tectonic plate, and often parallel an oceanic trench

25. the relief features or surface configuration of an area

26. ridge extend through the Atlantic, Indian, and South Pacific oceans: each is hypothesized to be the locus of seafloor spreading

27. mineral or organic matter deposited by water, air, or ice

28. the property or characteristic that produces unequal physical effects at different points in a magnet or storage battery

29. type of tectonic boundary where two plates are moving in the opposite direction.

Down

1. theory in which the lithosphere is divided into pieces, each move on the plastic asthenosphere to collide with, slide under, or move past adjacent pieces

2. part of Earth's lithosphere that covers the ocean basins

3. is a highly viscous layer between the crust and the outer core

4. is the simplest whole number ratio of atoms of each element present in a compound.

6. minerals and/or organic particles settle and accumulate to form a new material

11. one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge

12. chasm extending along the crest of a mid-ocean ridge, locus of the magma upwelling that accompany seafloor spreading

13. near a magnet, electric current, or moving charged particle in which a magnetic force acts on any other magnet, electric current, or moving charged particle

14. any long, narrow, steep-sided depression in the ocean bottom in which maximum oceanic depths (24,000–

36,000 ft)

16. a large geologic areas that are below sea level

17. the distribution of crystallographic orientations of a polycrystalline sample

18. type of tectonic boundary where two plates are moving past each other in opposite directions

19. the layer of igneous, sedimentary, and metamorphic rocks which form the continents

20. continental transform fault that runs a length of roughly 810 miles (1,300 km) through California

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