Forces Shaping Earth Earth’s Moving Plates Uplift of Earth’s Crust

Earth’s Moving Plates A. Geologists use earthquakes and surface rocks to indirectly observe Earth’s interior.

1. Seismic waves change speed and direction depending on the density and material they travel through.

2. Forces bring rocks formed deep within Earth to the surface.

3. Evidence suggests that the Earth is formed of different materials in layers.

B. Earth has four main layers.

1. Inner core – dense iron core; very hot and dense; solid iron center

2. Outer core – molten metal above inner core.

3. Solid layer that flows slowly like putty is the mantle. The mantle is the largest layer.

4. Outermost layer is the crust. The crust is made of Tectonic plate.

C. Earth’s structure – theories based on physical properties of density, temperature, and pressure that change with depth.

D. Earth’s moving plates are sections of the lithosphere, the rigid upper part of the mantle and crust.

E. Plate boundaries are the edges where plates meet.

1. Tension can pull plates apart, resulting in new lithosphere forming in the gaps.

2. Colliding plates could cause mountains to form as rock crumbles and folds.

3. Subduction occurs when a denser plate sinks underneath a less dense plate.

4. Shearing, or sliding causes faults and earthquakes as two plates slide past each other.

F. Plate movement theory – convection in the mantle circulates material and moves plates.

1. Ridge-push at mid-ocean ridges causes plates to slide down the slope.

2. Slab – pull happens as plates move away from mid-ocean ridges and become denser.

Section 2 Uplift of Earth’s Crust A. Mountains form in different ways.

1. Fault-block mountains- form from huge tilted blocks of rock separated from surrounding rock by large faults.

2. Folded mountains- formed by compressed forces folding rock layers.

3. Upward mountains- forces push up Earth’s crust and allow the sedimentary rock to erode, leaving igneous or metamorphic rock.

4. Over time, layers of lava can form a cone- shaped volcanic mountain.

5. Hot spots formed by plumes of magma in the mantle can cause under water volcanic mountains.

B. Isostacy principle indicates Earth’s crust and lithosphere float on the upper mantle. 1. Earth’s crust is thicker under mountains. 2. When mountains erode, the crust rises because the weight has been removed.