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Our natural resources 10 hp 2010 Earth and Earth processes -How do we know and how long have we known? Håkan Sjöström Department of Earth Sciences Study questions 1. 2. 3. 4. 5. 6. 7. 8. Which are the interacting Earth systems? When did approximately the layered structure of Earth form - and how? Describe shortly five processes on Earth that are related to Plate Tectonics What drives Plate Tectonics and what are the velocities of plate movements? Why are countries around the Pacific suffering from the threats of earthquakes and volcanism? How much energy and non-metallic + metallic resources are used annually in the US and in the whole world? What was the atmosphere like before 550 million years ago? What caused the major changes in carbon dioxide (CO2) and oxygen (O2)? What was the main restriction to a deeper understanding of Earth processes during the 17th century? From stardust to a rocky planet Layered structure (4.5) Hydrosphere (4.4) The moon is formed (3.0 -) Atmosphere The early atmosphere Ocean form 4,6 4,0 CO2 decreased with time Algae O2-rich atmoSphere forms oldest remaining crust Bacteria Gases released by volcanic activity 3 1,5 Late increase of oxygen (O2) by life (photosynthesis) – present level c. 400 million years 0,5 0 Todays surface of Earth • 2/3 covered by water. • 83% of land surface show human “fingerprints”. • 95% of the ocean floor has not been investigated • green house effect is 33°C. The interacting Earth Systems Spheres inside Earth Crust: 7-70km Litosphere Lithosphere Astenosphere Mesosphere etc or Astenosphere 410 km 71 63 660 km km 90 28 (solid but flowing) km Crust Mantle Core How can we see the internal layered structure? Direct observations to 1 km depth = 1% of the Lithosphere!! By the behaviour of seismic (earthquake) waves Earlier views on Earth 1600-1700: Catastrophism: Landscape formed by large catastrophes that no longer existed One reason: the condensed time scale, e.g. Bishop James Ussher; Earth formed 4004 B.P. (23 October) Buffon 1744 Earth is 74 047 years old radioactivity was not known until 1895 – no direct dating! The birth of modern geology James Hutton (1726-1797) Uniformitarianism* Plutonism Geological Cycle *“The present is the key to the past”. The results, therefore, of our enquiry is, that we find no vestige of a beginning no prospects of an end.” A great step forward: understanding the time Humans Based on: Fossils Rock correlation Refined by: Radiometric dating of rocks/minerals 65 144 248 354 443 540 Earth is 4 600 000 000 years old Flowers Dinosaurs between 248 - 65 Ma Insects Land plants Fishes Organisms with shells Organisms 4600 Continental Drift The precursor of Plate Tectonics Continental Drift - a hypothesis before its time based on observations Alfred Wegener 1912: The origin of Continents and Oceans. Supercontinent Pangaea started to break up about 200 million years ago. Continents "drifted" to their present positions. Continents moved through the ocean floors. Pangaea 200 million years ago Continental Drift: some Evidence 1.Geographic fit of South America and Africa 2.Fossils match across oceans 3.Rock types and structures match across oceans 4.Glacial features in the “wrong” place 1. The continent puzzle Tight fit of the continents, especially using continental shelves (at 900 m depth). 2. The match of fossils 3. Rock types and structures Correlation of mountains with nearly identical rocks and structures 4. The glacial features Glacial features of the same age restore to a tight polar distribution. Continental Drift: Reactions • Received well in Europe and southern hemisphere. • Rejected in U.S.; considered as speculations • Lack of a suitable mechanism crippled continental drift’s widespread acceptance. • Conflict remained unresolved because seafloors were almost completely unexplored.