Earth(physical prop)

• Towards the end of this era, the Northern Hemisphere was covered by glaciers, which has signaled the start of the Pleistocene Ice Age. This Ice Age may have lasted about 2 million years.
• During this period, humans records of humans were stone tools.
• Have you noticed that as you travel north, a greater number of stars remain above the horizon all night and as you travel south, additional stars become visible? These would not happen if the earth was flat.
• Pythagoras


  Greek philosopher and mathematician who thought the earth had a spherical shape
• Eratosthenes


  Greek astronomer who measured the earth's circumference
• Isaac Newton predicted that Earth was not a perfect sphere, reasoning that since the Earth was spinning rapidly, the equatorial portion swings outward, just as a ball on a string does when it is whirled around. As a result, the Earth bulges slightly at the equator and is slightly flattened at the poles.
• The Earth is not a perfect sphere due to its equatorial bulge. Our planet is also irregular in the sense that its surface has mountains and valleys both above and below sea level.
• Models of the Earth have been created to provide a convenient way of locating places. The "standard earth" was computed in terms of an oblate spheroid by J.P. Hayford in 1910.
• Eratosthenes' measurement of the Earth's circumference


  1. Knew the sun was directly overhead at noon on the first day of summer in Syene, 800 km south of Alexandria

  2. Carefully measured the extent to which the sun's rays slanted away from the vertical at noon in Alexandria

  3. Reasoned that 7.33° would be the same fraction of 360° as 800 km is of the circumference of Earth

  4. Calculated the circumference of the Earth to be 40,000 km
• Henry Cavendish


  English scientist who was the first to determine the mass of the Earth by experimentally measuring the gravitational constant in Newton's universal law of gravitation
• The strength of gravity can be used to calculate the gravitational pull between objects
• Latitude


  Lines drawn east to west around the Earth, numbered from 0° at the equator to 90° at the North and South Poles
• Longitude


  North-south lines drawn from the North Pole to the South Pole, with the prime meridian at 0° passing through Greenwich, England
• Longitudes or meridians are not parallel, they are farthest apart at the equator and get closer together as they reach the poles
• International Date Line


  The 180° meridian where east and west longitude lines meet, crossing this line going west adds one day
• Map


  A drawing of the Earth or part of the Earth on a flat surface
• Globe


  A spherical model of the Earth showing the sizes, shapes, and locations of continents and bodies of water
• Map scale


  Enables determining distance between places on a map compared to actual distance on Earth's surface
• Map symbols


  Drawings that stand for real places or things, explained in the map legend
• Topographic map


  Shows the 3D landscape of an area using contour lines to represent elevation
• Crust


  The thin outermost layer of the Earth where all life exists, composed of silicon, oxygen, aluminum, calcium, sodium, and potassium
• Mantle


  The layer beneath the crust, about 1,800 miles thick, made of heavy rock-like material
• Core


  The innermost layer of the Earth, mostly made of molten iron and nickel
• The crust varies in thickness, being thickest under continents and thinnest under oceans
• The deepest hole drilled into the crust is only about 8 km deep
• Mohorovicic Discontinuity (Moho)


  The boundary between the Earth's crust and mantle, discovered by Andrija Mohorovicic
• The mantle makes up about 80% of the Earth's volume
• The inner core is very dense due to intense pressure pushing iron and nickel particles tightly together
• The Earth's magnetic field may be due to the dense iron in the inner core
• Scientists think that the existence of the magnetic field around the earth may be due to the preasure of the dense iron in the inner core.
• The outer core is made mostly of molten iron and nickel.
• The outer core is thought to generate the Earth's magnetic field through convection currents.
• Convection Currents are caused when hotter material rises while cooler material sinks.
• The outer core is liquid because it is so close to the Earth's surface where temperatures are high enough to melt rock.
• The outer core is also called the fluid core.
• The outer core is thought to generate the Earth's magnetic field.
• The crust is the thinnest layer of the Earth, but it is also the most important because it contains all life on Earth.
• Convection currents are caused by differences in temperature, which can lead to movement within fluids or gases.
• The lithosphere is composed of the crust and uppermost part of the mantle.
• The mantle is composed mainly of silicate minerals, such as olivine and pyroxene.