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35 Cards in this Set

  • Front
  • Back
Theory (everyday usage)
a speculative or conjectural explanation; an unsubstantiated wild guess.
Theory (scientific usage)--
coherent explanation supported by a large body of objective evidence; validity of explanation testable by experiment and/or assessment of predictive ability; for example, the law of universal gravitation.
Scientific method --
orderly, logical collection and analysis of data about a specified problem; includes testing of tentative explanations, hypotheses; if repeated testing confirms hypotheses, then can propose as a theory, otherwise explanation is rejected and new hypotheses tested; theories subject to refinement by further testing and new data.
Origin of the Solar System
The Earth is thought to have formed by progressive bombardment of space matter to form a planetesimal, within the context of the solar nebula theory.
Solar Nebula theory.
higly unorganized nebula develops into the stellar disk , then forms rings as mass accumulates. Eventually, most of the nebula mass accumulates due to gravitational attraction to form the young star, as the mass in the rings accumulates to form the planets.
Hypotheses of Earth Accretion
suggests that the metalic core accreted first due to the high density of metallic meteors. This was then followed by accretion of the silicate mantle/crust, hence the entire process was heterogeneous.
The Homogeneous Accretion theory suggests that there was uniform bombardment of metallic and silicate meteors to form the Earth. This was later followed by whole scale melting of the Earth that allowed the dense metallic material to sink and the less dense silicate material to float, hence forming the Core and Mantle.
Studies of earthquakes
revealed that the Earth is a highly structured planet with a metallic core, a dense silicate-rich mantle and less dense silicate-rich crust.
geologists favor the homogeneous accretion theory
because there is evidence that early Earth experienced melting. The oldest rocks on Earth have an igneous origin, that is they formed from melted rock. The diagram below portrays the differentiation of the heavy and light elements to result in the highly structured Earth with a core, mantle and crust
Geochronology (ML-1).
generally accepted that this process occurred about 4.6 billion years ago. This hypothesis is based on our ability to recognize natural chronometers in clocks that are based on naturally radioactive elements, and our ability to read those chronometers.
Why do we not have rocks of this age on Earth?
is directly related to Plate Tectonics and Weathering, two processes that recycle rocks on our planet
Earth Rock Age
never been a rock from Earth that has yielded this very old age. In fact, this age is based on rocks collected on the Moon and meteorites. It is theorized that the Moon and Earth formed simultaneously, therefore, the age of Moon rocks probably also dates the age of the formation of Earth
Atomic abundances
elements that comprise 97% of the Earth's mass.
13.175
Earth size, mass and chemical composition.
Inner Core (solid)
Outer Core (Liquid)
Mantle
Crust
lower Mantle
Asthenophene
upper mantle
oceanic crust
continental crust
Equator: 6.367 x 108 cm
Poles: 6.378 x 108 cm
Mass: 5976 x 1024 g (1lb = 453.59 g)
S 3.8%
AL 1.4%
CA 1.5%
O 30.7%
Mg 14.2%
FE 32.9
Earth has gravity
due to it’s mass, and gravity is the force that drives Plate Tectonics. As well, it is gravity that contributes to Weathering, Water Flow, and all most other surface processes. The Earth also has a magnetic field because the core of the Earth is a dynamic electro-magnet. Due to electron flow in the molten outer Fe-rich core, the magnetic field forms a shroud that protects the Earth from highly ionized, high-energy solar winds. Without this magnetic shroud, the Earth’s atmosphere would not exist.
Earth’s magnetic field
produces a shroud around the planet that extends deep into space.magnetic field deflects Solar wind.magnetic field protects the Earth from the Solar wind.magnetic field is distorted by the Solar wind
Earth is
lumpy with continental masses that are separated by deep basins.
topography
(above sea-level)
bathymetry
(below sea level)
gravity is caused by
the amount of mass under any given point, the gravity on Earth varies slightly from place to place. For example, if you look at the map below, the bright red domains are places where the gravity is higher than average. These places generally occur where there are mountain ranges, such as the Andes Mt. on the west side of South America.
geology also has an effect on the local magnetic field
can be observed through Magnetic Anomaly Mapping.very small changes in magnetic properties of rocks on Earth.magnetic stripes that occur in the ocean basins. It was these stripes that led to the Theory of Plate Tectonics
deepest hole ever drilled
12.2 km, while the average thickness of Continental Crust is about 35 km.
Earth’s interior
NOT based on direct observation of rocks. In fact, we know more about asteroids from direct observation than we do about the Earth’s interior. Gravity causes great pressure within the Earth, making it technologically impossible to drill to extreme depths.
how do we know that the Earth has an Fe-rich core? How do we know how big the core is? Where is the bottom of the crust, or the mantle?
By transfer of **mechanical energy** and how that energy is recorded at the surface. The energy sources is Earthquake seismic waves. The same waves that destroy buildings and kill people, have been used to map the Earth’s interior.
seismic energy waves are transferred
(Like the balls in a game of 8-ball)
through the earth by mechanical vibrations. The vibrations are both compressional (P-waves) and shear (S-waves). P-waves travel faster than S-waves and can pass through rock and liquid. However, the S-wave can not travel through liquid. The velocity of the waves is dependent on the density of the rock, and the rock density is dependent on chemical composition and compaction (due to depth). The graph below shows variations in seismic wave velocity as they pass from the Lithosphere, Asthenosphere and Core. Note that the S-wave velocity goes to zero at the Mantle-Core boundary, indicating that the outer core is liquid.
S-waves (form a single earthquake)
from that quake are then recorded around the world, but not within the 103 degree region directly opposite the quake. This is due to the S-waves being absorbed by the liquid outer core, therefore forming the S-wave Shadow Zone.
The Earth’s Interior
Mantle: Peridotite (ultramafic rock)
Core: Fe-Ni metallic alloy
upper 350 km of Earth
part of the Earth that mostly impacts life at the surface. The upper mantle in this region consists of the Asthenosphere (hot, ductile rock) and is overlain by the Lithosphere. The lithosphere includes the upper most part of the Upper Mantle and the Crust. The lithosphere is where Plate Tectonics occurs. The crust consists of Continental and Oceanic portions. They differ in composition and thickness, but both ride on the rigid layer of upper mantle.
Oceanic crust
Thin: 10 km
Relatively uniform
Stratigraphy
•Ocean Sediments
•Basalt
•Gabbro
•Ultramafic (mantle)
Continental Crust
Thicker: 20-90 km, Average ~35 km Highly variable composition
–Average composition ~ granitoid
interior of the Earth
is very hot. In fact, the core of the Earth is about 5000 degrees C. That heat moves slowly from the interior to the surface by Convection, Conduction and Advection
Transfer of thermal energy
the heat in the Earth moves slowly to the surface via Conduction, Convection and Advection. Conduction involves heat moving by transfer of thermal energy through the solid rock, much like the heat that is transferred from the bottom to the top of a skillet. Slow movement of the ductile mantle from deeper to shallower levels in the earth is the result of thermal convection. As the hot mantle rises, the cooler mantle rock sinks forming large convection cells.
process of Advection
involves the one-way movement of heat when magma moves toward the Earth’s surface.
Where is the place with the highest geothermal gradient?
That place is Yellowstone National Park. This is a place where magma is within 10 km of the Earth’s surface, so the geothermal gradient is greater than 70 degrees per km
4 kilometers is equal to
2.8 miles.
lithosphere
broken into several tectonic plates. The red lines on the map are the plate boundaries. There are three types: Convergent, Divergent and Transform. Convergent boundaries are where plates are moving toward one another. Divergent is where they are moving apart, and transform is where plates are moving laterally past each othe