The Unofficial Exam I Review Page Geo 460 101 Fall Semester 2013 Exam I will cover Lectures 2 Cosmos through 6 Age of the Earth as posted on Sakai All questions pertain to those materials covered in lecture Questions will be in the form of short answers diagrams and short essays Here are the topics you should be familiar with What is the age of the universe This is based on what 1 13 8 billion years based on radioactive decay of elements 4 7 How do we think the Moon formed How do we think the Earth formed 2 3 Co formation Moon and Earth condensed together form the original nebula that formed the solar system or from condensing of debris from collisions of large planetesimals early in the hisotry of the Solar System Capture The moon formed elsewhere at some time was later captured by the gravitational field of the Earth Collision Ejection A planetesimal the size of Mars struck the Earth ejecting large volumes of matter A disk of orbiting material of Earth material and the planetesimal held in orbit by the Earth s gravitational pull eventually condensed to form the Moon in Orbit around the Earth What is the average density of the Earth How does the density of the whole Earth compare with that of the crust What does that tell us about the make up of the interior of the Earth Density of earth 5 5 g cm3 The density of the inner earth is higher than the crust How else do we know that the interior of the earth is denser than the Crust 5 Lighter densities float to the top keeping more dense layers on the bottom How does the density of the Earth compare with that of our Moon Why 6 The moon has much less iron than Earth which makes it less dense What is the most abundant element of the whole Earth Earth s Crust Why the difference How can we estimate the original composition of the Earth Most abundant element of the Earths Crust is Oxygen What do we mean by planetary differentiation 8 A process that occurs during the formation of planetary bodies What do we mean by differentiation by fractional crystallization 9 When magma rises above a certain depth the dissolved materials may crystallize at certain pressures and temperatures The resulting solids remove various elements from the melt and the melt is thus depleted of those elements What do we mean by differentiation by partial melting 10 Since materials melt at different temperatures raising temperatures high enough to melt silicates can result in those materials with higher melting temperatures to crystallize out of the liquid 11 1 2 3 4 5 What is Bowen s reaction series explain in detail What happens when magma cools Different minerals crystallize in a specific sequence as magma cools Olivine and Ca rich plagioclase form first taking Fe Mg and Ca with them from the melt The re maining melt is more silicic in concentration As the magma cools further pyroxene amphibole then biotite crystals form At this point plagioclase formed at these lower temperatures contain more Na less Ca At temperatures between 650C and 850 C only 10 melt remains and Si rich minerals such as Quartz K feldspar and muscovite crystallize Discontinuous reaction series Olx Pyx Amph Biot K feldspar muscovite quartz path note that the first mineral is a isolated Si O tetraheda the second is a chain of SiO2 and the third is double chains the fourth 2 D and the last 3 D silicates Continuous Reaction Series Ca rich to Na rich plagioclase sequence 12 What silicate minerals dominate the Mantle The Continental Crust What two rock names do we use to typify the mantle and continental crust Crust Minerals Quartz SiO2 K feldspar Use Granite or Rhyolite for crust rocknames Mantle Olivine pyroxine rocks peridotite What is a Si tetrahedron 13 The Si minerals consists of a Si atom bound covalently to four O atoms Te oxygen atoms ocupy the cor ners of a geometraical shape called a tetrahedron The silicon atom is at its center Silica tetrahera can join together by sharing oxygen atoms The Si tetrahedron bears a negative electraical charge enabling it to form compounds with cations Independent tetrahedra Single chains Double Chains Sheets 3 D Framework 14 What are isolated single and double chain sheet and framework silicates What are some of the main Si minerals we discussed that relate to Bowens Reaction Series Nesosilicates isolated tetrahedron Olivine Insosilicates single chain pyroxene group Insosilicates Double chain amphibodle group Phyllosilicates Sheets Micas and Clays Tectosilicates 3D Framework Quartz Feldspars Zeolites What is the relationship between silica content and density 15 As silica increases density decreases Silica tetrahedron limits elements with higher densities to fit into open spaces What affects the type and size of minerals in an igneous rock 16 Different cooling rates for different mineral species viscosity levels extrusive or intrusive 17 Why we think our solar system is a 2nd or 3rd generation system stars are element factories where do elements come from Nebula Hypothesis Solar system is much richer in heavy elements than would be predicted for a first generation star such as our sun heavy elements heavier than Fe can only be made in a supernova exploding star since the earth has many heavy elements there must have been a earlier star that exploded to supply these elements during the formation of our solar system 18 Where does Earth s internal heat come from What is the difference between convection and con duction Convection heat is carried from one object by a fluid motion in gas or liquid most efficient Main process by which heat is moved from the interior to the exterior regions of the Earth Convection implies fluid be havior where hot material rises due to its lower density and cold materials sink due to its higher density Conduction where one object transfers heat directly through contact with another object 19 What are the oldest materials dated on Earth What is the age of the oldest rocks on Earth Why the difference What is the age of the Earth How do we know that What is radioactive decay When does radioactive decay begin How can we derive an age of the Earth without dating Earth itself The oldest rock formations of Earth come from cratonic rocks from Canada Australia South Africa and India Oldest material dated on Earth are detrital zircons in metamorphosed sandstone in the Jack Hills Gneiss Terrane of Western Australia the oldest of these dated to 4 4 Ga 20 Age of Earth 4 5 Billion years 21 22 Radioactive decay occurs at a fixed rate unaffected