Forces Shaping Earth Notes Mrs. Seay 6 th Grade Science

 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 Earth is formed of different materials in layers.

 B. Earth has four layers.

 Inner core—dense iron core; very hot and dense.

 Outer core—molten metal above the inner core

 Solid layer that flows slowly like putty is the mantle.

 Outermost layer is the crust.

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

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

 Plate boundaries are edges where plates meet.

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

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

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

 Shearing causes faults and earthquakes as two plates slide past each other.

 Plate movement theory—convection in the mantle circulates material and moves plates.

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

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

 Mountains form in different ways.

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

 Folded mountains form by compression forces folding rock layers.

 Upwarped mountains—forces push up Earth’s crust and allow the sedimentary rock to erode, leaving igneous or metamorphic rock.

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

 Hot spots formed by plumes of magma in the mantle can cause underwater volcanic mountains.

 Isostacy principle in dicates Earth’s crust and lithosphere float on the upper mantle.

 Earth’s crust is thicker under mountains.

 When mountains erode, the crust rises because the weight has been removed.