Presentation on theme: "Earth's Surface 3.3 Sedimentary rocks form from earlier rocks."— Presentation transcript:
Earth's Surface 3.3 Sedimentary rocks form from earlier rocks.
Some rocks form from rock particles Sediment ( something that settles )are materials that settle out of water or air Most sedimentary rock forms from loose material that gets pressed together or cemented into rock Loose pieces of rocks and minerals, plants and animal remains Sedimentary rocks develop from layers of sediments that build up on land or underwater.
Forming and Transporting Rock Particles Particles, from the size of boulders to sand to clay, are broken away from rocks by the action of water and/or wind. Rainwater washes away rock particles and carries them to streams and rivers, which eventually empty into lakes or oceans. Strong winds also pick up sand and rock dust These rock particles settle on the land or at the bottom of rivers, lakes, and oceans. The sediments form layers as larger particles settle first, followed by smaller ones.
Forming Loose Sediments into Rocks Sediments composed of rock particles may get pressed together to form rock. Layers get buried and overlying layers apply pressure to the sediments underneath. Pressure can form rocks out of small particles of sediment, such as silt and clay. Particles can be held cemented together by minerals that have crystallized between them.
Some rocks form from plants or shells Coal is made up of remains of plants. Unusual because it forms from plants instead of earlier rocks. Started forming millions of years ago in swamps. Plant remains fell upon the remains of earlier plants. Layers of other sediments buried the layers of plant remains. The weight of the sediments above pressed the plant material into coal.
Limestone Limestone is made up of carbonate minerals Shells and skeletons of ocean organisms are formed of these minerals Organisms die Their shells and skeletons settle on the ocean floor as layers of sediment Layers become buried, pressed together, and cemented to form limestone.
The famous white cliffs of Dover, England, consist of a type of limestone called chalk. Began to form millions of years ago when the land was under the ocean. The rock developed from shells of tiny organisms that float in the ocean.
Most limestone comes from shells and skeletons of ocean organisms. Organism's shells and skeletons are formed with the minerals from dissolved rock that that are present in ocean water Limestone forms from material that came from older rocks. Limestone is produced when coral organisms build their skeletons on top of each other. The rock does not go through a loose-sediment stage.
Some rocks form when dissolved minerals re-form from water Substances can dissolve in water and then re-form as the water evaporates. Some sedimentary rocks are made up of minerals that crystallized. Some are in solid form. Rainwater picks up pieces of minerals and rock particles and carries them into streams and rivers where they settle Some of the minerals dissolve in the water and are carried along with it. Water often flows through cracks in rock that is near Earth’s surface. Water dissolves limestone. As water flows and drips through the cave, some of it evaporates and the new limestone makes odd and beautiful shapes. Sometimes minerals crystallize along the edges of lakes and oceans where over time they form layers of sedimentary rock. Rock salt and gypsum form in this way
Sedimentary rocks show the action of wind and water Sedimentary rock is laid in layers, with the oldest layers of sedimentary rock on the bottom. A geologist studying layers of sedimentary rocks can tell something about what conditions were like in the past A layer with smaller particles on top shows that the water carrying the sediment moved quickly then slowed down as in a flood. Ocean or wind currents leave ripples in sand which later becomes sandstone. Mud cracks in clay indicate wet periods followed by dry periods.