Notes: Rocks and Fossils February 18, 2004

Rocks are made of mixtures of minerals and other materials Rocks are made of mixtures of minerals and other materials Igneous Rocks – form when molten material cools and hardens below or on Earth’s surface Igneous Rocks – form when molten material cools and hardens below or on Earth’s surface Sedimentary Rocks – form when particles of other rocks or the remains of plants and animals are pressed and semented together Sedimentary Rocks – form when particles of other rocks or the remains of plants and animals are pressed and semented together Metamorphic Rocks – form when an existing rock is changed by heat, presure, or chemical reactions Metamorphic Rocks – form when an existing rock is changed by heat, presure, or chemical reactions

Petrified Fossils – fossils in which minerals replace all or part of an organism Petrified Fossils – fossils in which minerals replace all or part of an organism Mold – a hollow area in sediment in the shape of an organism of part of an organism Mold – a hollow area in sediment in the shape of an organism of part of an organism Cast – a copy of the shape of an organism Cast – a copy of the shape of an organism Other Types of Fossils – Carbon film, trace fossils, and preserved remains Other Types of Fossils – Carbon film, trace fossils, and preserved remains

Relative Age – its age compared to the ages of other rocks Relative Age – its age compared to the ages of other rocks Absolute Age – the number of years since the rock formed Absolute Age – the number of years since the rock formed Law of Superposition – ub horizontal sedimentary rock layers the oldest layer is at the bottom. Each higher layer is younger than the layer below it (relative age) Law of Superposition – ub horizontal sedimentary rock layers the oldest layer is at the bottom. Each higher layer is younger than the layer below it (relative age)