1. 8th Grade Science Unit 8: Changes Over Time
Lesson 3: Forces Behind Change
Vocabulary of Instruction

2. 1. Asthenosphere
Is the soft -plastic like- layer of the Earth’s mantle on which the lithospheric plates float and move around.

3. 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.

4. 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.

5. 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.

6. 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.

7. 6. Land Subsidence
The sinking or subsiding of land surface as a result of geologic processes or human activities.

8. 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.

9. 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.

10. 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.

11. 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.

12. 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.

13. 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.

14. 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.

15. 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.

16. 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.

17. 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.