EATS1010 - The Dynamic Earth and Space Geodesy Lecture 3

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York University
Earth, Space Science and Engineering
ESSE 1010
Gary Jarvis

Lecture 3 To Be or Not to Be a Planet Definition of a Planet 1. Large enough to be rounded by its own self gravitational forces 2. Not a satellite of another object in the solar system 3. Has cleared its orbit of space debris Definition of a Dwarf Planet Pluto: Not considered a planet because it spins around the Sun yet it does not pick up all the space debris in its orbit. Earth • One of ~200 relatively minute chunks of rock and gas (i.e. planet and their moons) • Their planet from the Sun • Trapped in orbit about the Sun by the Sun’s gravity • It drifts through space at a speed of ~30km/sec Formation of Earth • Earth formed by accretion of space debris left over form the formation of the sun about 4.6 billion years ago o Collisions of planetsimals (tiny planets) orbiting the Sun Accretion of Earth: Accretion  growth  increased mass  larger gravitational attraction  further accretion, growth & larger gravity still. • Increasing gravity  increasing speeds of incoming objects o –(10-15 km/sec) • Enormous Kinetic Energy o All converted to heat upon impact • Heating  Melting of early Earth • Melting  Differentiation o Heavier iron metals sank o Lighter stony silicates rose **what is the difference between accretion and differentiation? Differentiated Earth • An iron core cloaked in a mantle of rocky silicone material (mostly silicon and oxygen) • Cooling o Solid mantle • Partial melting o Radioactive decay of Potassium, Thorium and Uranium Twice Differentiated Earth 3 Chemically distinct layers • Crust • Mantle • Core Early crust bombarded from space Evidence for Early Crustal Disruption • All evidence on Earth has been lost due to ongoing geological activity: o Erosion (wind, water, ice) o Volcanic eruptions o Sediments (deposited in lakes and oceans) o Large scale recycling of surface (plate tectonics) Impact Craters • Dominant geological activity on Earth for the first 600 million years • Knowledge based on: o Explosion craters o Labatory experiments • Earth’s forces force of gravity accelerates meteoroids towards earth as they approach. Escape Velocity • Escape velocity: the velocity needed for an object to escape the gravitational influence of Earth’s mass • An object throw upwards at speeds less then the Escape Velocity wil
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