Transcript 8. Mid-Ocean Ridge

th
8
Grade Science
Unit 8: Changes Over Time
Lesson 3: Forces Behind Change
Vocabulary of Instruction
1. Asthenosphere
• Is the soft -plastic likelayer of the Earth’s
mantle on which the
lithospheric plates float
and move around.
2. Continental Drift
• The theory that all continents were once connected in a single
large landmass that broke apart about 200 million years ago
and drifted slowly to their current positions.
• German scientist Alfred Wegener was the first to come up with
this theory.
3. Convergent Boundary
• A plate boundary where two plates move towards each other
and collide.
• The plate collisions that occur in these areas can produce
earthquakes, volcanic activity, and crustal deformation.
4. Divergent Boundary
• A plate boundary where two plates move away from each other,
forming either mid-oceanic ridges or rift valleys.
• Divergent boundaries between oceanic plates form submarine
mountain range such as the Mid-Atlantic Ridge; volcanic
activity in the form of fissure eruptions; shallow earthquake
activity; creation of new seafloor and a widening ocean basin.
5. Erosion
• Process in which surface materials (fragments of
rocks and soil) are worn away and transported
from one place to another by agents such as
gravity, water, wind, and glaciers.
6. Land Subsidence
• The sinking or subsiding of land surface as a result
of geologic processes or human activities.
7. Lithosphere
• Solid and rigid layer of Earth consisting of the crust and part
of the upper mantle. It is about 100 km thick.
• The lithosphere is brittle enough at some locations to fracture
and produce earthquakes.
8. Mid-Ocean Ridge
• Area where new ocean floor is formed when lava
erupts through cracks in the Earth’s crust.
• It is a divergent plate boundary.
9. Neap Tide
• A tide with the least difference between low and high tide that
occurs when the Earth, moon and sun are arranged
perpendicular to each other (pull at right angles to the Earth).
• Neap tide comes twice a month, in the first and third quarters
of the moon.
10. Pangaea
• The large ancient landmass that was composed of the
entire continents joined together that broke apart 225
million years ago and gave rise to today’s continents.
11. Plate Tectonics
• The theory that Earth’s
crust and upper mantle
are broken into plates
that floats and move
around on a plastic like
layer of the mantle.
12. Sea-Floor Spreading
• Hess’s theory that new
seafloor (oceanic crust)
is formed when magna
is forced upward
toward the surface at a
mid-ocean ridge.
13. Spring Tide
• A tide with the greatest difference between high and low tide
that occurs when the Earth, moon and sun are arranged in a
straight line, during the new and full moon phases.
• Spring tides happen twice a month.
14. Transform Boundary
• A plate boundary where two tectonic plates slide, grind, and
past each other in opposite directions along a transform fault.
(also known as transform fault boundary, sliding boundary,
or conservative plate boundary).
• San Andres Fault in California is an example of transform
boundary.
15. Uplift
• This process result from
convergent boudaries
where land is being
raised to a higher
level, as during a period
of mountain building.
• Examples of mountain
ridges include the
Rockies and the
Himalayas.
16. Volcanic Mountains
• Mountains formed when
molten -lava rock- and other
volcanic material reaches the
Earth’s surface through a
weak crustal area and piles up
into a cone shaped structure.