The Composition and Layers of the Physical Earth Planet Earth The Composition and Layers of the Physical Earth

Chapter Objectives The Earth as a system How large is the Earth? What is Earth’s shape? Evidences..? The spheres of the Earth and their compositions. Atmosphere Hydrosphere Geosphere

Earth as a System Earth is a dynamic body with many separate but highly interacting parts – or spheres. Earth as a system – Nearly endless array of subsystems. e.g. – hydrologic cycle, carbon cycle Sources of Energy Sun – Drives external processes Weather and climate, Ocean circulation, & Erosional processes Earth’s Interior – nuclear, chemical, & thermal energy drives internal processes Volcanoes, Earthquakes, & Mountain building Humans are part of the Earth system

Earth’s Size Earth’s Circumference – distance around the earth was first measured by Eratosthenes 2000 years ago. Measured the distance between Egyptian cities of Alexandria and Syrene. Measured the sun’s angle at noon at each location. Difference in angle is a fraction of a circle. Multiple distance by fraction to get circumference. Obtained 46,250 km – very close to the real 40,000 km circumference

Eratosthenes’ Method

Earth’s Numbers Equatorial Polar Diameter Circumference 12,174 km

The Earth’s Shape The shape of the Earth is usually thought of as a Spheroid Oblate Sphere The Earth’s Shape The shape of the Earth is usually thought of as a From observations & measurements by earth scientists we know that the Earth is slightly flattened at the poles, and slightly budging at the equator. Thus, the shape is called a(n)

Earth looks spherical from space Earth’s Shape Because the Earth spinning on its axis – It bulges at the equator It flattens at the poles Earth looks spherical from space

Evidence of Nearly Spherical Shape As we now know that the Earth is NOT flat (as it was once believed). Columbus, Magellan The position of the sun and the stars depends on the position on Earth, thus the earth has to be curved. On of the best known stars in the North Star – The angle of Polaris in the sky increases as one travels towards the North Pole, where it is directly overhead (90⁰) POLARIS 42⁰ At North Pole At ALCS

Evidence Cont.… Ship masts appear 1st on the horizon. Earth’s shadow is curved when seen during a lunar eclipse. *Astronauts have photographed Earth from space*

Star Trails (Time Lapse Photography) Evidence for Earth’s Rotation on its axis

Spheres of the Earth Geosphere: Consists of all the rock and fluid inner layers of the Earth

Spheres of the Earth Geosphere: Consists of all the rock and fluid inner layers of the Earth Hydrosphere: Consists of all the water on Earth’s surface; oceans, rivers, lakes, streams, etc. Covers ~71% of surface.

Spheres of the Earth Geosphere: Consists of all the rock and fluid inner layers of the Earth Hydrosphere: Consists of all the water on Earth’s surface; oceans, rivers, lakes, streams, etc. Covers ~71% of surface. Atmosphere: Consists of the “shell” of gases that surrounds the earth

Average Chemical Compositions ESRT – Front Cover

Percent Composition of the Atmosphere Our atmosphere is mostly Nitrogen (78%), followed by Oxygen (21%). CO2 makes up less than 1%.

Properties of the Atmosphere ESRT – Page 14

Ozone Depletion The ozone absorbs harmful UV rays from the Sun. Depletion caused by CFC’s (ChloroFluoroCarbons) found in aerosols, Styrofoam, and refrigerants. Problem from ozone depletion is increased skin cancer in humans.

Atmospheric Phenomena Aurora Borealis in Ionosphere

Hydrosphere All the water on the Earth covers ~71% of the surface Freshwater (2%) – Rivers, Lakes, Streams, & Marshland Marine (97%) – Saltwater Oceans Ice (1%) – Continental and Mountain/Alpine Glaciers

Structure of Earth’s Geosphere Page 28 in Text ….

Compositional Zones Crust – The thin outer most zone Continental & Oceanic crust make up 1% of the Earth’s Mass. The Lower boundary is the MOHO – or Mohorovicic Discontinuity MOHO

Compositional Zones Crust – The thin outer most zone Continental & Oceanic crust make up 1% of the Earth’s Mass. The Lower boundary is the MOHO – or Mohorovicic Discontinuity Mantle – Below the crust Denser than crust 66% of Earth’s mass Silly-putty like

Compositional Zones Crust – The thin outer most zone Continental & Oceanic crust make up 1% of the Earth’s Mass. The Lower boundary is the MOHO – or Mohorovicic Discontinuity Mantle – Below the crust Denser than crust 66% of Earth’s mass Silly-putty like Core – Composed mainly of Iron and Nickel. Outer core is a dense liquid Inner core is a dense solid 33% of Earth’s mass

Structural Zone Three compositional zones are divided into five structural zones: Lithosphere – Crust and cool brittle upper mantle. 15 – 300 km thick Asthenosphere – Less ridged layer with more ability to flow due to enormous amount of heat and pressure (plasticity). 200 – 250 km thick Stiffer Mantle – Layer od solid mantle rock Outer Core – Dense liquid, mostly iron Inner Core – Dense solid of iron and nickel

ESRT – Pg 10 What happens to the density from the crust towards the inner core? What happens to pressure as you go towards the core? What happens to temperature as you go towards the core? Which layers are liquids (above melting point)? What is the depth of the boundary between the Mantle & Outer Core?

How do we know? From Seismic Waves Scientists studying earthquakes have found that seismic waves travel through the Earth’s interior at different speeds and directions. The differing speeds are due to the different densities of the existing zones or layers. Think about trying to run through air vs trying to run through water… These Seismic Waves are called P (primary) and S (secondary) waves.

Seismic Waves The Seismic Waves change speed and direction as they pass through layers of different densities. Notice the S-waves do not travel through the liquid outer core… http://www.classzone.com/books/earth_science/terc/content/visuali zations/es1009/es1009page01.cfm