Layers of the Earth

Inner Core The super-hot solid inner layer of iron and nickel under extreme pressure

Outer Core The liquid layer of melted iron and nickel that surrounds the inner core.

Mantle The thickest layer. This layer is made up of hot, dense rock – silicon, aluminum, iron, magnesium, and oxygen. This layer rises, cools, sinks, warms up, rises, etc.

Crust The rocky shell that covers the earth’ surface. The shell is broken up into plates that move apart or ground together to push up mountains, create volcanoes, and produce earthquakes.

Internal Forces of Change

Continental Drift Plate Tectonics The theory that the land of the earth was once connected as one large super continent (Pangaea) and has moved “drifted” to its current locations (still moving) Plate Tectonics The theory that the crust of the earth is broken up into plates (8 major and many minor) that “float” on the mantle

Subduction – When a sea plate and continental plate collide, the heavier sea plate DIVES under the lighter continental plate. The sea plate then is heated and becomes magma which escapes through volcanoes.

Accretion – slow process that occurs when a sea plate SLIDES under a continental plate. This causes debris which makes continents grow outward.

Spreading – When sea plates pull apart leaving a rift, or deep crack Spreading – When sea plates pull apart leaving a rift, or deep crack. Magma wells up between the two plates to make underwater volcanoes and ridges.

Folding – when moving plates squeeze the earth’s surface until it bends the layers of rock.

Faulting - When moving plates grind past each other, creating cracks in the curst.

Earthquake – sudden, violent moving of plates along a fault where built up pressure suddenly snaps and shifts.

Ring of Fire – area along the edge of the Pacific Ocean that is a zone of frequent earthquakes and volcanoes.

Volcano – mountains formed by lava (magma) that breaks through the earth’s crust.

Subduction & Accretion: Convergent Continental-Oceanic Plates Click on the underlined headings to see animation: Subduction & Accretion: Convergent Continental-Oceanic Plates Folding & Faulting: Convergent Continental Plates Spreading Oceanic Divergent Plates

External Forces of Change

Weathering – process that breaks down rocks on the earth’s surface into smaller pieces Physical Weathering – Form of weathering that occurs when large masses of rock are broken down into smaller pieces. Example: Cracks in rocks fill with water and then freeze. Ice expands and cracks the rocks.

Chemical Weathering – Form of weathering that occurs when the make-up of the rock is changed by transforming minerals or combining with new elements. Example: carbon dioxide in the air dissolves limestone.

Erosion is the wearing away of the earth’s crust by water, wind, and glaciers. Wind erosion – movement of dust, sand, and soil from one area to another. Plants help prevent this.

Glacial erosion – large bodies of ice move slowly across the earth’s surface. As the glaciers move they pick up rocks and soils in their path. As the glacier retreats it can also leave fields of debris behind.

Water erosion – fast-moving water cuts into the land as it flows downstream. Ocean waves can also erode coastal cliffs. WATER is the most significant cause of erosion.