33Sedimentary RocksFormed from sediments (rock fragments, mineral grains, animal & plant remains) that are pressed or cemented together or when sediments precipitate out of a solution.
34These sediments are moved by wind, water, ice or gravity. Sedimentary RocksThese sediments are moved by wind, water, ice or gravity.Sedimentary rocks represent 7% of the Earth’s crust, but they cover 70% of the Earth’s surface.Sedimentary rocks are fossil-carrying rocks.
35What turns sediments into solid rock? Water or wind breaks down and deposits sediment (erosion & deposition)
36The heavy sediments press down on the layers beneath (compaction)
37Dissolved minerals flow between the particles and cement them together (cementation)
38How were most of the sedimentary rocks in the Puget Sound area deposited? Glaciers about 1500 years ago.
39How can sedimentary layers help us understand the age of fossils? As sedimentary rocks are deposited, they form horizontal layersScientists know that the layers on top (and the fossils in the top layer) are YOUNGER than the fossils in lower layers.
403 Types of Sedimentary Rocks: Clastic (also called Detrial)—made of broken pieces of other rocks
413 Types of Sedimentary Rocks: Organic—remains of plants and animals are deposited in thick layersExamplesFossil rich limestone is made from the shells of ocean animals; used to make chalk
423 Types of Sedimentary Rocks: Chemical—minerals dissolved in lakes, seas, or underground waterMineral crystals are made as the shallow water that has flooded the bottom of Death Valley evaporates. Click on image for full size (66K JPG) Courtesy of Martin Miller, University of Oregon
43ExamplesLimestone made when calcite mineral precipitates from sea waterRock Salt—made from evaporation of sea waters
44Rocks that have changed due to intense temperature and pressure Metamorphic RocksRocks that have changed due to intense temperature and pressure“Meta” means “change” and morphosis means “form” in GreekIgneous, sedimentary and other metamorphic rocks can change to become metamorphic rocks
45What occurs in the Earth to change these rocks? Pressure from overlying rock layersHigh heat, but not enough to melt the rockRocks may be flattened or bent or atoms may be exchanged to form new minerals.
46*You can think of metamorphic rocks as a squished peanut butter & jelly sandwich in your lunch.
47How are metamorphic rocks classified? Foliated—mineral grains are flattened and line up in parallel bandsExample: gneiss formed from rearrangement of minerals in granite into bands
48How are metamorphic rocks classified? Non-Foliated—No bands are formedExample: marble formed from limestone
49Where do metamorphic rocks usually form? Where magma intrudes relatively cool rockNear colliding plates (near mountain ranges)Places that are covered miles thick with other rock causing pressureWhen hot water intrudes rockWhere a meteorite strikes Earth (rare)Where lightning bolts strike rocks (rare)