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1 Earth and its rocks 2 © Zanichelli editore 2015 Earth’s structure 3 © Zanichelli editore 2015 The surface of the Earth The surface of planet Earth is made up of the ocean floors and continental masses. On the ocean floors there are ridges, volcanic mountain ranges, and trenches, the lowest points of the Earth’s crust. 4 © Zanichelli editore 2015 Endogenous and exogenous processes Endogenous processes occur inside Earth and generate the ocean floors and continents. Exogenous processes are determined by the actions of the atmosphere, hydrosphere and biosphere, and they shape what is produced by the endogenous dynamic. 5 © Zanichelli editore 2015 The inner structure of Earth /1 6 © Zanichelli editore 2015 The inner structure of Earth /2 Earth is made of layers, from the surface to the nucleus we can find: • the crust; • the mantle; • the core. The thin and rigid lithosphere (crust + upper mantle) rests on the fluid asthenosphere (lower mantle). 7 © Zanichelli editore 2015 Earth’s magnetic field The outer core generates the planet’s bipolar magnetic field which extends beyond the surface of the Earth and protects it from solar winds. 8 © Zanichelli editore 2015 Earth’s internal energy The engine of endogenous processes is Earth’s internal thermal energy, which is partly derived from the heat of accretion of our planet and partly derived from radioactive substances in Earth’s crust and mantle. Convective cells of the asthenosphere transfer this heat to the upper parts. 9 © Zanichelli editore 2015 Lithosphere and tectonic plates The lithosphere is divided into tectonic plates which are dragged over the asthenosphere by convective movements. 10 © Zanichelli editore 2015 The lithosphere is dynamic Tectonic plates move and grow near ridges where the oceanic lithosphere is shaped and are then destroyed in oceanic trenches. Endogenous processes occur along plate boundaries. 11 © Zanichelli editore 2015 Igneous and metamorphic rocks Endogenous processes create magma, which solidifies at depth (magma) or appears on Earth’s surface (lava). The solidification of magma and lava creates igneous rocks. The transformation of preexisting rocks gives rise to metamorphic rocks. 12 © Zanichelli editore 2015 The exogenous dynamic 13 © Zanichelli editore2015 Exogenous agents shape the landscape Exogenous agents, like air, water, wind and living beings, cause the weathering and erosion of rocks, but also transportation and sedimentation of debris. The exogenous dynamic is activated by solar heat that warms up the Earth, in a non-uniform way depending on the time of year and geographic location. The effects of this dynamic triggered by the Sun are different and also depend on: climate, geography and exogenous agents. 14 © Zanichelli editore 2015 Sedimentary rocks Sedimentary rocks arise from the cementation of erosion debris which are transported and deposited elsewhere by exogenous agents. They are nearly always stratified and may contain fossils. 15 © Zanichelli editore 2015 The soil Soil is the most external and thinnest layer of Earth’s crust and is made up of solid, liquid and gaseous substances. It is formed by a process called «pedogenesis», which occurs over a long period of time with degradation of parental material by atmospheric agents. 16 © Zanichelli editore 2015 The history of Earth and life 17 © Zanichelli editore 2015 The depth of geological time Geological time is measured on two different scales: • the relative geologic time scale reconstructs the sequence of geological and biological events without dates; • the absolute geological time scale dates geological events in millions and billions of years (for example, Pangea is dated back to 250 millions years ago). Relative dating is based on the sequence of sedimentary layers and the fossils they contain. Index fossils allow temporal correlations to be made between different areas; the facies fossils help retrace paleoclimate and paleogeography. 18 © Zanichelli editore 2015 The geochronographic scale /1 Geochronologic unit Eon Duration (millions of years) 2000 Era Period Epoch Age 0.01 The geochronographic scale consists of 4 eons, called Hadean, Archean, Proterozoic and Phanerozoic, divided into eras, periods, epochs and ages. 19 © Zanichelli editore 2015 The geochronographic scale /2 20 © Zanichelli editore 2015