Great Ideas in Science: Lecture 9 – Earth as a Planet Professor Robert Hazen PROV 301 Great Idea: Earth, one of the planets that orbits the Sun, formed 4.5 billion years ago from a great cloud of dust and gas.

Today: Key Ideas About Earth Earth, one of the planets that orbits the Sun, formed 4.5 billion years ago from a great cloud of dust and gas. 2. The surface of our planet changes constantly; no feature is permanent. 3. Earth is still changing, due to the slow convection of soft, hot rocks deep within the planet. 4. Earth materials move in cycles; a change in one cycle affects others.

Clues to the Origin of the Solar System Solar System = Objects gravitationally bound to the Sun

Clue #1: Planetary Orbits Features of solar system All planets orbit in the same direction All planets orbit in the same plane Most planets rotate in the direction of orbit

Clue #2: Distribution of Mass Almost all mass is in the Sun (99.9%) Two types of planets Small, rocky inner planets [“Terrestrial”] Gas giant outer planets [“Jovian”] Other objects Moons, asteroids, comets

A Hierarchy of Scientific Ideas Fact (a confirmed observation) Hypothesis (an educated guess) Law (a predictive mathematical description of nature) Theory (a well established explanation of nature)

The Nebular Hypothesis

Rocky (Inner) Planets Mercury, Venus, Earth, Mars These planets are rocky, dense, and relatively small.

Gas Giant (Outer) Planets Jupiter, Saturn, Uranus, Neptune: These planets are rich in gas, low density, and much larger than the terrestrial

Pluto and the Plutoids Pluto has only 0.3% of Earth’s mass Pluto has three moons Could be a captured comet or asteroid? Is it a planet?

Asteroids, Comets, and Meteors “Small” rocky bodies They orbit the Sun Many in asteroid belt Comets They’re like dirty snowballs They have highly elongated orbits Stardust and Deep Impact missions Meteors and Meteorites Original solar system material Watch for meteor showers!

The Formation of Earth The Great Bombardment

Earth’s Layers (think onions) Heat was produced from collisions and by radioactive elements. Dense material sank to the center, while lighter material rose to the surface The result: A layered structure Core Mantle Crust

Volcanoes and Earthquakes: Evidence of Earth’s Inner Forces Volcanoes: Magma breaks through surface

Volcanoes and Earthquakes: Evidence of Earth’s Inner Forces Rocks breaks along a fault. Energy is transmitted as a wave through solid rock. Tsunamis are ocean waves after big earthquakes.

The Case of the Disappearing Mountains Old Young

James Hutton at Jedburgh Scotland Deep Time James Hutton at Jedburgh Scotland ca.1790

Deep Time Sediments Burial Uplift

Plate Tectonics Great Idea: Earth is constantly changing, due to the slow convection of soft, hot rocks deep within the planet.

Plate tectonics – 6 lines of evidence Physiology: Similar shapes of continents

Plate tectonics – 6 lines of evidence Physiology: Shape of continents Seismology: Distribution of earthquakes

Plate tectonics – 6 lines of evidence Physiology: Shape of continents Seismology: Distribution of earthquakes Geology: Distribution of rocks and fossils

Plate tectonics – 6 lines of evidence Physiology: Shape of continents Seismology: Distribution of earthquakes Geology: Distribution of rocks and fossils Oceanography: Sea floor topography Bruce Heezen and Marie Tharp

Plate tectonics – 6 lines of evidence Physiology: Shape of continents Seismology: Distribution of earthquakes Geology: Distribution of rocks and fossils Oceanography: Sea floor topography Volcanology: Ages of Atlantic volcanoes <5 95 75 55 125

Plate tectonics – 6 lines of evidence Physiology: Shape of continents Seismology: Distribution of earthquakes Geology: Distribution of rocks and fossils Oceanography: Sea floor topography Volcanology: Ages of Atlantic volcanoes <5 95 75 55 125

Plate tectonics – 6 lines of evidence Physiology: Shape of continents Seismology: Distribution of earthquakes Geology: Distribution of rocks and fossils Oceanography: Sea floor topography Volcanology: Ages of Atlantic volcanoes Paleomagnetism of sea floor rocks

New Support for Plate Tectonics Satellite measurements of the distance between continents North America and Europe are separating at ~5 cm per year

Earth’s Tectonic Plates

Three Main Boundary Types Plate Boundaries Three Main Boundary Types Divergent Convergent Transform

Divergent Boundaries

Convergent Plate Boundaries Three Types: 1. Ocean-ocean

Convergent Plate Boundaries Three Types: 1. Ocean-ocean 2. Continent-continent

Convergent Plate Boundaries Three Types: 1. Ocean-ocean 2. Continent-continent 3. Ocean-continent

Transform Plate Boundary

Another Look at Volcanoes and Earthquakes Volcanoes Occur: 1. At Divergent Plate Boundaries 2. Close to Convergent Plate Boundaries 3. Above Hotspots

Another Look at Volcanoes and Earthquakes Earthquakes Occur at: Transform Plate Boundaries Convergent boundaries

Earth’s Geochemical Cycles Earth materials move in cycles; a change in one cycle affects the others. 1. Atoms recycle; they’re used over and over. Reservoirs (Aluminum can) Hydrologic cycle Atmospheric cycle 2. Energy flows through the system.

Geochemical Cycles Account for all the repositories of that substance. Document processes by which the substance moves from repository to another. Gold

The Carbon Cycle

Atmospheric Cycle Air mass: Uniform temperature and moisture Weather: State of the atmosphere Climate: Long-term average of weather

The General Circulation of the Atmosphere Circulation powered by Sun: Air is heated and then rises at the Equator. Air cools and sinks at the poles. The prevailing winds are caused by Earth’s rotation.

Five variables define the state of atmosphere, i.e. the weather: Temperature Air pressure Humidity Cloudiness Prevailing winds

Climate Climate, unlike weather, refers to gradual change over long periods Influences on climate include: Large bodies of water Ocean currents Mountain ranges Position of tectonic plates Solar output Greenhouse gases

The Water (Hydrologic) Cycle The total amount of Earth’s water is constant; the same atoms cycle from one reservoir to another. The total volume is ~1.4 billion km3 Oceans 97.3% Lakes and Rivers 0.01% Groundwater 0.6% Ice Caps & Glaciers 2.1% Atmosphere 0.001% All life 0.00004%

How does water move among reservoirs?

How does water move among reservoirs?

Ocean Currents Redistribute heat across planet

Cycle tied to Earth’s tilt and orbit Ice Ages As the ice caps and glaciers grow, the sea level drops. Cycle tied to Earth’s tilt and orbit

Two facts about water use A human requires about 2 liters of water per day to survive The average American uses about 6,000 liters of water per day

The Water Table The water table will drop when discharge exceeds recharge (like a bank) In the US we “mine” about 100,000,000 gallons of water every day (more than the recharge) Artificial recharge helps Urbanization and pollution hurt