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27 PLANET EARTH Salt Lake Temple granite Top When was this granite formed? Don’t forget to take Exam 3! Do all mineral systems give the same age for this granite? If not what events are they recording? PS 100 -- Chapter 27 1 Sun is thought to be about 5 billion years old Rocks from the Moon have been dated at 4.6 billion years old A. B. is thought to be the age of the Earth and Moon C. Oldest rocks on Earth are about 4.0 billion years old Age Top Age Base K-Ar Hornblende 500 ºC 30 my 30 my K-Ar Biotite 300 ºC 28 my 28 my Fission Track Zircon 225 ºC 20 my 10 my Fission Track Apatite 100 ºC 11 my 6 my 2 Because the Moon is older than the earth. Earth & moon are about the same age, but the Earth’s surface is constantly reworked whereas the Moon’s surface is not. Because radiation exposure on the Moon makes the rocks older. 3 4 PS 100 -- Chapter 27 What is the Earth made of? Why are Rocks on Earth Younger? Closure T PS 100 -- Chapter 27 This PS 100 -- Chapter 27 Mineral Why were astronauts able to find older rocks on the moon than any found on Earth? How old is the Earth? Base System It has a Tectonic System It has a Hydrologic System Feldspar Mostly Oxygen, Silicon, and Iron Atoms combine to form “Minerals” Quartz Mica PS 100 -- Chapter 27 5 Minerals combine to form “Rocks” PS 100 -- Chapter 27 6 1 Common Igneous Rocks What are the main types of Rocks? IGNEOUS ROCKS – Form from hot, liquid magma SEDIMENTARY ROCKS – Form as layered deposits in oceans, lakes, and on land GRANITE BASALT METAMORPHIC ROCKS – Form when pressures, temperatures and fluids change rocks in the solid state Why is granite generally lighter in color than basalt or peridotite? PS 100 -- Chapter 27 Because granite has lower transition metal content Because granite is full of air pockets Because granite has larger grains PS 100 -- Chapter 27 SHALE SANDSTONE CONGLOMERATE LIMESTONE 9 SLATE Pebbles & cobbles Precipitates out of water PS 100 -- Chapter 27 10 Formed from Shale Formed from Sandstone GNEISS Sand-sized particles QUARTZITE Clay-sized particles Why are Earth & Venus so Different? Common Metamorphic Rocks 8 Common Sedimentary Rocks C. Why is granite generally lighter in color than basalt or peridotite? Lowest in Si Highest in Fe,Mg Highest Density 7 PS 100 -- Chapter 27 B. Lower in Si Higher in Fe, Mg Higher Density PERIDOTITE A. High in Si Low in Fe, Mg Low Density Formed from Shale or Granite MARBLE Formed from Limestone PS 100 -- Chapter 27 11 PS 100 -- Chapter 27 12 2 Continents Characteristics of Continents Why does the Earth have continents? Because it has WATER Water is necessary to make granite, and granite is what continents are made of and Plate tectonics to pull sediment that contains water down into the Earth where it can combine to form the minerals in granite PS 100 -- Chapter 27 Composed mostly of rocks high in silica (granite, gneiss) Low density Rocks can be as old as 4 billion years Rocks may be highly deformed Continents have several distinct regions 13 PS 100 -- Chapter 27 14 Shield Shield Oldest part of continent Rocks highly deformed Roots of ancient mountain belts Sometimes called the “basement” Stable Platform Mountain Belt PS 100 -- Chapter 27 15 PS 100 -- Chapter 27 16 Stable Platform PS 100 -- Chapter 27 17 Relatively flat lying, undeformed sedimentary rocks Broad domes and basins Sediments lie on top of basement (rocks found in shield) PS 100 -- Chapter 27 18 3 Mountain Belts PS 100 -- Chapter 27 19 Continental Shelf & Slope Rugged Topography Youngest part of continent Folded and faulted rocks Found along margins of continents May have active volcanoes PS 100 -- Chapter 27 20 Ocean Basins The Edge of the Continent Continental Shelf is the part of the continent under water Continental Slope is the drop-off into the deep ocean basin PS 100 -- Chapter 27 21 Oceanic Ridges Composed mostly of basalt High density Rocks younger than 200 million years Rocks mostly undeformed Ocean Basins have several distinct regions PS 100 -- Chapter 27 22 Abyssal Hills & Plains Long underwater mountain ranges Common eruptions of basalt Youngest part of ocean basin High heat flow Generally have a rift valley along the crest of the ridge PS 100 -- Chapter 27 23 PS 100 -- Chapter 27 24 4 Trenches – narrow, deep, usually next to the continents, & oldest part of ocean basin PS 100 -- Chapter 27 25 Ocean Islands & Seamounts PS 100 -- Chapter 27 26 How did all of these features form? PS 100 -- Chapter 27 27 5