By Michael Nau and Elizabeth Dorsey

Weathering vs. Erosion  Erosion involves movement and weathering does not.  Weathering is the main agent in erosion. s/misc/gweaero.html

Weathering  CHEMICAL: involves a chemical change in some of the minerals in the rock  PHYSICAL: when the rock physically brakes down  Weathering makes sediment (fragments of material) which is moved by deposition (wind, water and ice) s/misc/gweaero.html

Erosion  When forces of nature move soil and rock  SHEET EROSION: when rain washes away top soil on sloped land. Gravity (the force that pulls stuff down) is the force that makes eroded material slide down hill  Erosion from the Colorado River formed the Grand Cannyon. m

Rock Cycle  ROCK CYCLE: a model of the formation, breakdown and reformation of rocks  Igneous rocks form by cooling magma  Metamorphic rocks form from heat and pressure  Sedimentary rocks form by sediment being compacted into layers (may contain fossils, skeletons of dead plants/animals)

Different parts of the Earth were once under the ocean  For example, if you found a shark tooth on a hill, you could assume the hill was once underwater. s/misc/gweaero.html

Laws and Scales  The Law of Superposition says that sedimentary layers form with the oldest layers on the bottom and newest on the top.  The Geological Time Scale shows the different periods the Earth went through. s/Geologictime.html