Looking into the Earth (Week/Day 2)
Looking into the Earth (Week/Day 2) GEOLOGY103
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This 4 page Class Notes was uploaded by Monica Weisenbach on Saturday February 7, 2015. The Class Notes belongs to GEOLOGY103 at a university taught by Peter Panish in Fall. Since its upload, it has received 206 views.
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Date Created: 02/07/15
Week 2 Radiometric Dating Radiometric dating works because all things are slightly radioactive A note on atoms the of protons of electrons neutrons can vary different isotopes of atoms and the atomic mass number is the of protons and neutrons combined Parent radioactive elements decay into stable daughter elements Halflife the amount of time it takes for one element to decay by half Uranium238 gtgt Lead206 and Carbon14 gtgt Nitrogen14 used for inorganicorganic things respectively Other Dating Principles Principle of Superposition is the idea used often before radiometric dating and still for rocks that cannot be dated using that method that the further down something is the older it is Note that this works only really with sedimentary rocks Similar features like fossils between areas of known age and those of unknown age can help determine relative age Techniques of Seeing the Ocean Sounding is the process of throwing weighted ropes overboard and measuring the length when bottom was hit A very tedious process with doubtful accuracy and not many taken Echo Sounding is the process of throwing highfrequency sound waves at the bottom of the ocean and recording the echoes with a hydrophone This provides a continuous depth profile along the ship s track but it s only two dimensional Seismic Reflection Profile is done by a sound source and hydrophone towed behind the ship using a lower frequency sound that penetrates the ocean bottom layers This can reveal the sediments underlying the ocean crust Side Scan Sonar is like the Echo Sounder but wider with a 60km patch of seafloor measurement This produces 3D images of the seafloor Multibeam Survey Sonar is a more sophisticated version Satellites can pull data about the ocean floor by measuring minute variations of the ocean surface which reflects the bottom The average depth of the ocean is 38 km and the greatest depth is 11 km Earth s Interior Earthquakes let off seismic energy which radiate out and away from its foci There are 3 types of waves Rayleigh Pwaves and Swaves Rayleigh waves travel along the surface Pwaves travel fast through the Earth Swaves are slower and cannot go through liquid or gas Note With media of different densities light rays and others are bent when changing mediums This has helped scientists to understand the core of Earth Swaves cannot go through liquid the outer core is liquid stopping all swaves from passing through and casting an swave shadow zone on the other side It s a big part of the reason about how the size of the outer core is known Pwaves on the other hand is focused by the inner core producing two pwave shadow zones That s part of how it is known that the inner core is solid Paleomagnetism When magma cools it may have some magnetic particles in it When the magma gets past its Curie temperature the magnetic particles will freeze in their current orientation of the magnetic field This allows scientists to infer what the magnetic field looked at at the time of freezing This is one part of the evidence used to prove continental drift The Earths poles have switched at least once in This is further evidence of a liquid outer core if the convection pattern changes the fields can change although no one is entirely sure why On the sea floor the midatlantic ridge spews out lava that cools and records the magnetic field in symmetrical stripes on either side of the valley Sea Floor Spreading Midocean ridges are bisected by valleys where new lava comes up and forms new crust The Atlantic is widening and the Pacific is shrinking What about spreading ridges in the Pacific Subduction is the answer the Pacific plate is subducting against the American plates being destroyed faster than it is being made Remember subducting is when one plate goes below another plate divergent is when two plates are pulling apart and convergent is when two plates are colliding and pushing upwards Fun fact the North Atlantic opened up first as it has areas of crust older than the South Atlantic
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