Earth History Benchmark Study Guide 2014

Sedimentary RocksSedimentary Rocks: Class of rocks that are formed when a metamorphic rock or igneous rock undergoes weathering and erosion and is broken into small pieces and deposited into a sediment basin forming flat layers. The Principle of Superposition states that sedimentary rock layers on the bottom formed, or were deposited, first and are older than layers that formed on the top.Those small pieces are then glued together due to compaction and cementation to form a new rock (kind of like cement). Common examples include, but are not limited to: Sandstone, Limestone and Shale. Sedimentary rocks are the ONLY rocks that can contain fossils. Limestone is sedimentary rock that contains Calcite (calcium carbonate) that comes from respiration or the shells of organisms living in the sea. Geologists use an acid solution to test for Calcite because it fizzes when it comes in contact with acid.

Principle of Superposition

Weathering Weathering and Erosion is the process of weathering and erosion is what continually changes the face of the Earth. All rocks and surfaces on the Earth are affected by the combination of weathering and erosionWeathering: All weathering deals with the breaking up of rocks and minerals into smaller pieces. There are two types of weathering: Physical (Mechanical), and Chemical

Physical (Mechanical) Weathering is the type of weathering that occurs when a rock is physically broken up due to physical forces. Examples of physical weathering include: Abrasion rocks rub or hit against each other due to the force of gravity and break down Frost wedging water in the cracks of a rock freezes and then expands, pushing the rock apart.Root wedging the type of weathering that

Abrasion

occurs when a rock is physically broken apart by the actions of living things (usually plants and their roots).

Chemical Weathering the type of weathering that occurs when a rock is broken down by a chemical reaction. Most common form of Chemical Weathering is in the form of acid rain that literally eats away at rocks

ErosionErosion is the process that sorts loose and weathered rock by size, and carries it to a new site. The smaller the rock size, the farther the rock will travel. Water, wind, and glacial ice combined with the force of gravity can cause erosion. The youngest (top) layers of sediments usually get eroded first. The driving force behind erosion is GRAVITY!  There are several types of erosion:Water: water running (due to gravity) takes weathered rock and deposits it elsewhere. Wind: wind picks up fine sediment and deposits it elsewhere. Gravity keeps large sediments from moving, but small particles (sand, silt and clay) can be blown around by the wind.Glaciers (Glaciation): process by which giant slabs of ice form and grow and recede. During this process, the ice rips and tears the land beneath it apart. As the glacier melts, it deposits the eroded sediment forming different landforms

Rock Classification Sizes

Chemical Weathering

FossilsFossil any remains, trace, or imprint of animal or plant life preserved in Earth’s crustIndex fossil a fossil that characterizes a particular period of time. To be considered an index fossil, must have been distributed over a wide geographical area, and have lived for only a short period of time. Index fossils are useful for indicating the ages of the rock layers.Geologic Time Geologic time is the measurement of time from the formation of Earth to the present. The Earth is estimated to be 4.6 billion years old. Geologic time is broken down into 4 Eras: Cenozoic, Mesozoic, Paleozoic and Precambrian. Eras are broken down into Periods. Periods are based on major evolutionary events that can be determined by fossil records. Periods are further broken down into Epochs.

Uniformitarianism a theory that says geological processes observed in the past are the same as those observed today, and will continue to happen in the futureIgneous RocksIgneous rocks: Class of rocks that are formed when magma or lava cools and solidifies. Igneous literally means fire hence the name Igneous Rock: rocks that hardened from molten (on fire) rocks. Any of the other two types of rock can potentially become an igneous rock if they are melted back into magma (liquid rock) and harden again. Common examples of Igneous rocks include, but are not limited to: Granite, Basalt and Obsidian. The presence of crystals usually indicates an igneous rock. The size of the crystals indicate the rate at which the magma or lava cooled. If the magma cooled slowly underground (intrusive) the crystals tend to be larger and more visible. If the lava cooled quickly at or near the surface of the Earth (extrusive), then the crystals tend to be smaller and harder to see.

Earthquakes and VolcanoesVolcanoes result from the subduction of more dense oceanic plates under less dense continental plates. Volcanoes occur when water from the ocean is pulled under the less dense continental plate and creates pressure in the magma in the mantle under the continental crust. This pressure builds up forcing the magma towards the surface, eventually causing an eruption.

Earthquakes result from the shifting of the Earth’s plates and the buildup of tension in the crust that gets released

Volcanoes and Earthquakes often occur near tectonic plate boundaries.

Continental Drift Continental drift - Theory originally proposed by German Meteorologist Alfred Wegener, that proposed that the Earth’s continents are not fixed in one position on the Earth, rather they are moving around the surface of the Earth. Evidence of Continental Drift: There are many forms of evidence that back up this theory 1. The coast lines of the Continents (especially Africa and South America) line up like pieces of a puzzle. Those pieces can be put together to form one giant supercontinent - we believe this supercontinent, Pangea, existed 250 million years ago.2. Rock Samples and fossils taken from the coasts of South America and Africa match up perfectly, suggesting the two continents were once together 3. Fossil records in Antarctica show evidence of tropical plants. The only way this is possible is if Antarctica was in a different location at one point in history.4. Coal found in cooler climate areas now formed from when those areas were at one point located at the equator and were tropical, and glacial scars found in dry desert

areas of Africa

Theory of Plate TectonicsData obtained from seismic wave studies from large scale earthquakes has given scientists a virtual picture of what the inside of the Earth looks like. We know the Earth consists of 3 main layers:Crust The outer solid and thinnest layer of the Earth, and is made of continental crust which is about 60 miles thick, and oceanic crust only 10 miles thick at its thinnest. The crusts and the upper mantle make up the lithosphere, which houses the tectonic plates. Mantle The layer of the Earth below the crust. The mantle extends below the crust for about 1,800 miles. Temperatures range from about 1000 OC to 3000 OC. The temperature difference in the mantle causes convection currents in the semi-liquid material are responsible for moving the tectonic plates.Core The Outer Core is the layer of the Earth below the mantle. Consists of mostly liquid Iron at a temperature between 4000 OC to 5500 OC. Heat from the outer core heats up the Earth’s mantle causing the convection currents that drive plate tectonics. Inner Core The innermost layer of the Earth. Consists almost entirely of Solid Iron and some nickel at a temperature roughly equivalent to the surface of the sun (6000 OC). Intense pressure from the surrounding layers keeps this layer solid.Tectonic Plate BoundariesThe movements of the plates result in the creation of earthquakes, volcanoes, mountain ranges on land and ridges and trenches in the oceans. There are three main types of plate boundaries:Divergent Boundary where two plates move apart from each other. Divergent boundaries most often result in the formation of mid-ocean ridges and are responsible for sea floor spreading.  The newest sea floor will be at the trench in the middle, and the older sea floor near the continents (Image A)

Convergent Boundary place where two plates come together. If two continental plates collide it will result in mountain ranges. If a less dense continental plate collides with a more dense oceanic plate, the ocean plate will go under the continental plate in a process called subduction. Subduction leads to the formation of Volcanoes and can cause Earthquakes (Image B)

Transform Boundary is a place Where two plates neither collide nor move apart, instead they literally slide past each other. Transform boundaries often result in earthquakes (Image C)MountainsMountains form over millions of years from forces that have pushed up or uplifted the rocks they are made of. Plate movement provides the force needed to create a mountain.

Metamorphic RocksMetamorphic rocks: Class of rocks that are formed when either an Igneous rock or Sedimentary rock undergo INTENSE heat and pressure, BUT DO NOT MELT. The effect of heat and pressure warps the rocks causing changes in their crystals, shape and coloration. Metamorphosis means a great change, hence the name Metamorphic rock: a sedimentary or igneous rock that has undergone great change. Common examples of Metamorphic rocks include, but are not limited to: Slate, Marble, and schist.

Divergent Boundary

Convergent

Boundary

Transform Boundary