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Review: Rocky Planets 2 Moon Formation Homework Due Friday Morning 9am Today in class Matter Fundamentals Atoms Elements Ages of Rocks I Review: Rocky Planets I The formation of our Moon I The Nature of Matter I The Age of Earth (and the solar system) Radioactive Decay Potassium-40 Age of Earth Review: Rocky Planets 2 Moon Formation Matter Fundamentals Atoms Elements Review: Rocky Planets 2 Ages of Rocks Radioactive Decay Potassium-40 Age of Earth Question concepts Review: Rocky Planets 2 Question #1: While no liquid water currently exists on Mars’ surface, long-lived liquid water existed on the surface in the distant past. Moon Formation Question #2: On Earth, the carbon dioxide content of the atmosphere is regulated to give a stable greenhouse effect because more carbon dioxide leads to more water in the atmosphere and thus more formation of carbonate rocks. This removes the excess carbon dioxide from the atmosphere, bringing it back to equilibrium. Ages of Rocks Question #3: Among the rocky planets, Earth is the only to exhibit plate tectonics. Others exhibit some evidence of volcanoes, craters, and erosion (typically by wind). Matter Fundamentals Atoms Elements Radioactive Decay Potassium-40 Age of Earth Review: Rocky Planets 2 Moon Formation Matter Today in class I The formation of our Moon I The Nature of Matter I The Age of Earth (and the solar system) I Radioactive Decay Fundamentals Atoms Elements Ages of Rocks Radioactive Decay Potassium-40 Age of Earth Giant Impact formation of our Moon Problems with Moon formation: I Too large to be captured from other orbit I Too low density to have formed with Earth The Clue: Composition of most of the Moon very similar to the outer layers of the Earth The hypothesis: I Mars sized planetesimal impacted Earth after it had differentiated, blasting off outer layers. I Material that stayed in Earth orbit coalessced to form Moon, I All debris was accreted or ejected. Review: Rocky Planets 2 Moon Formation Matter Fundamentals Atoms Elements Ages of Rocks Radioactive Decay Potassium-40 Age of Earth Review: Rocky Planets 2 Moon Formation Matter Question concepts Fundamentals Atoms Elements Ages of Rocks Question #4: A major motivation for the giant impact scenario for the formation of the Moon is the similarity of the Moon’s composition to the outer layers of the Earth. Radioactive Decay Potassium-40 Age of Earth Review: Rocky Planets 2 Moon Formation Matter Fundamentals Atoms Elements The Nature of Matter Ages of Rocks Radioactive Decay Potassium-40 Age of Earth Fundamental components of matter quarks up down Review: Rocky Planets 2 Moon Formation electron Matter Baryons: uud proton udd neutron Electrons: I negative electrical charge I very small mass (1/2000 of proton or neutron) Protons and Neutrons (Baryons) I Made of quarks combinations of up and down quarks I positively charged I most mass of matter I make up atomic nucleus Fundamentals Atoms Elements Ages of Rocks Radioactive Decay Potassium-40 Age of Earth Nuclei and Atoms Review: Rocky Planets 2 Moon Formation Matter Fundamentals Atoms Elements Ages of Rocks Radioactive Decay Potassium-40 Age of Earth Review: Rocky Planets 2 Moon Formation Matter Question concepts Fundamentals Atoms Elements Ages of Rocks Question #5: The nucleus of an atom is very small compared to its overall size. The size comes mostly from the region over which the electon ”cloud” is spread. Radioactive Decay Potassium-40 Age of Earth Elements and Isotopes I Elements have different chemical properties due to different number of protons (and therefore electrons) I Name of an element is just an alias for how many protons it has (see periodic table) I A given element can have several different numbers of neutrons – called different isotopes. Review: Rocky Planets 2 Moon Formation Matter Fundamentals Atoms Elements Ages of Rocks Radioactive Decay Potassium-40 Age of Earth Question concepts Question #6: The name of an element is related to the number of protons in the nucleus. This is the number that increases one by one left-to-right and top-to-bottom on the periodic table. This is also the number of electrons that an atom of this element generally has, and determines the chemical properties of the element. Question #7: The name of an element is related to the number of protons in the nucleus. The total number of protons and neutrons is indicated by saying a number after the name. For example, carbon-14 (also written 14 C) has 6 protons and 8 neutrons for a total of 14 protons and neutrons. Question #8: The name of an element is related to the number of protons in the nucleus. The total number of protons and neutrons is indicated by saying a number after the name. For example, carbon-14 (also written 14 C) has 6 protons and 8 neutrons for a total of 14 protons and neutrons. Review: Rocky Planets 2 Moon Formation Matter Fundamentals Atoms Elements Ages of Rocks Radioactive Decay Potassium-40 Age of Earth Review: Rocky Planets 2 Moon Formation Matter Fundamentals Atoms Elements How do we measure the age of a Rock? Ages of Rocks Radioactive Decay Potassium-40 Age of Earth Review: Rocky Planets 2 Moon Formation Matter Fundamentals Atoms Elements How do we measure the age of a Rock? Radioactive Decay! Ages of Rocks Radioactive Decay Potassium-40 Age of Earth Radioactive Decay Review: Rocky Planets 2 Radioactive decay arises through changes in the particles in the nucleus. Changes in the number of protons and neutrons. electron Moon Formation Matter Fundamentals Atoms Elements Ages of Rocks Radioactive Decay Potassium-40 Age of Earth Carbon−14 Nitrogen−14 half-life: The amount of time for half of a material to decay easily measured and not effected by temperature, etc for Carbon-14, half-life is 5730 years. Potassium-40 decay Review: Rocky Planets 2 Moon Formation Matter Fundamentals Atoms Elements Ages of Rocks Radioactive Decay Potassium-40 Age of Earth Why Potassium-40? (19 protons, 21 neutrons, 21 19 K) I half-life 1.25 billion years (decent fraction of Earth age) I decay product Argon-40 (18 protons, 22 neutrons, 22 Ar) 18 is an non-reactive gas (can’t form into rock) I Any Argon-40 in a rock must come from Potassium-40 decay decay of potassium-40 is also the largest source of radiation in your body Review: Rocky Planets 2 Moon Formation Matter Question concepts Fundamentals Atoms Elements Ages of Rocks Question #9: Argon is an example of a material that does not become part of rocks when they form because it is a non-reactive gas rather than a solid. Radioactive Decay Potassium-40 Age of Earth Age of Earth Review: Rocky Planets 2 Moon Formation Matter Fundamentals Atoms Elements Ages of Rocks Radioactive Decay Potassium-40 Age of Earth Oldest rocks on Earth are about 4 billion years old, with the oldest small grains around 4.4 billion years old. Oldest rocks on the Moon are also about 4.4 billion years old Oldest rocks in the solar system (recovered meteorites) are about 4.55 billion years old - leftovers of material that formed the rocky planets Review: Rocky Planets 2 Moon Formation Question concepts Question #10: A rock can be dated by comparing the amount of a radioactive isotope to the amount of its decay product in the rock. The amount of the first isotope decreases over time and the amount of the product increases. At the half-live there is an equal amount of radioactive and product material. Matter Fundamentals Atoms Elements Ages of Rocks Radioactive Decay Potassium-40 Age of Earth