NEW “PLANETOID” - SEDNA (Inuit Goddess of the Sea) Current Distance~100 AU Perihelion Distance~75 AU Mass~1/2 Pluto Eccentricity0.85 Semi Major Axis~500 AU Period11,000 years Aphelion Distance~925 AU Inclination to Ecliptic12 Degrees

EARTH AS A PLANET Chapter 7

SOME PROPERTIES of EARTH Semi major Axis1.00 AU Period1.00 year Mass5.98 x kg Diameter12,756 km Escape Velocity11.2 km/s Rotation Period23h 56m 4s Surface Area5.1 x 10 8 km 2 Atmospheric Pressure1.00 bar

EARTH as a PLANET l Only planet with water in liquid form. l Composition: iron, silicates, oxygen. l Density: highest in Solar System. l Interior: 4 major layers – inner core, outer core, mantle, crust.

EARTH as a PLANET l Only planet with water in liquid form. l Composition: iron, silicates, oxygen. l Density: highest in Solar System. l Interior: 4 major layers – inner core, outer core, mantle, crust. l Magnetic Field and Magnetosphere: Earth behaves as if it had a bar magnet inside it.

MAGNETOSPHERE and VAN ALLEN BELTS

The MAGNETOSPHERE SHAPE

EARTH’S STRUCTURE – HOW DO WE KNOW IT?

SEISMIC WAVES l Earthquakes produce two kinds of waves that travel through our planet. ä P (pressure) waves are longitudinal waves analogous to those produced by pushing a spring in and out. ä S (shear) waves are transverse waves analogous to waves produced by shaking a rope up and down.

SEISMIC WAVES l Earthquakes produce two kinds of waves that travel through our planet. ä P (pressure) waves are longitudinal waves analogous to those produced by pushing a spring in and out. ä S (shear) waves are transverse waves analogous to waves produced by shaking a rope up and down. ä P waves travel through solids and liquids (5-6 km/s). ä S waves cannot travel through liquids (3-4 km/s). ä Velocity of waves depends on density of material in which they travel. Velocity is faster in higher density materials.

S and P WAVE PATHS

FLASHCARDFLASHCARD P WAVES MOVE AT ABOUT 5 KM/S. HOW LONG WILL IT TAKE A P-WAVE TO REACH THE OPPOSITE SIDE OF EARTH AFTER AN EARTHQUAKE? (RADIUS OF EARTH IS 6500 KM) A) ABOUT 4 SECONDS B) ABOUT 4 MINUTES C) ABOUT 40 MINUTES D) ABOUT 400 MINUTES

EARTH’S STRUCTURE l Under Oceans Crust ä 6 km thick. Basalts (volcanic rock, Si, O, Fe, Al, Mg). l Under Continents Crust ä 20 to 70 km thick. Granite (volcanic silicates).

Crust Mantle OuterCore InnerCore EARTH’S STRUCTURE l Mantle ä Down to 2900 km. Solid with some melting. ä Ejected volcanoes allows study. l Core ä 3500 km radius. ä Outer core is liquid. Inner core dense and solid. ä Inner core rich in heavy elements - Fe, Ni, S.

Crust Mantle OuterCore InnerCore EARTH’S STRUCTURE l Structure indicates that Earth is differentiated which suggests Earth was once molten so heavier elements could sink to core.

PLATE TECTONICS l Earth’s crust consists of about 12 plates.

PLATE TECTONICS l Energy escaping from the interior drives the plates (few cm/year). 50 million years from now

PLATE TECTONICS l Where plates interact, dramatic changes occur in Earth’s crust. ä Rift Zones: Plates pulling apart. Material rises from mantle to fill spaces (volcanoes). E.g. Mid Atlantic Ridge.

PLATE TECTONICS l Where plates interact, dramatic changes occur in Earth’s crust. ä Subduction Zone: Two plates come together, one forced down and melts. Earthquakes and volcanoes common along subduction zones.

PLATE TECTONICS l Coastal BC is on the upper part of a subduction zone.

SAN ANDREAS FAULT

ACTIVE SITES on EARTH’S SURFACE

CONTINENTAL DRIFT

FLASHCARDFLASHCARD AT 2 CM/YEAR, HOW LONG WOULD IT TAKE A TYPICAL PLATE TO TRAVERSE THE PRESENT WIDTH OF THE ATLANTIC OCEAN, ABOUT 6000 KM? A) 3 X 10 6 YR B) 1.2 X 10 7 YR C) 3 X 10 8 YR D) 1.2 X 10 9 YR

< 10 km, most atmosphere here. (N 2 78%, O 2 21%, Ar 1%, traces H 2 O, CO 2 )Troposphere km, cold (-50ºC), cloudlessStratosphere km, O 3, absorbs UV radiationOzoneLayer Atmosphere very thin, constant leakage of H and He > 100 km

GREENHOUSE EFFECT l CO 2 content of atmosphere is critical for its role in retaining heat from Sun. l Greenhouse Effect: ä Earth absorbs sunlight and re-emits it as infrared (IR) radiation (Earth acts like a blackbody). ä CO 2 transparent to sunlight but absorbs IR acting like a blanket. ä The more CO 2, the hotter Earth is.

GREENHOUSE EFFECT and GLOBAL WARMING l Greenhouse effect has raised Earth’s average temperature by 23ºC. l Without the greenhouse effect, Earth’s average temperature would be below freezing and Earth would be in a constant global ice age.

GREENHOUSE EFFECT and GLOBAL WARMING l CO 2 levels are increasing. l Prediction: rising CO 2 levels will lead to global warming with uncertain consequences.

Vegetation map l Rainforests extract CO 2 l Destruction rainforests l This plus increasing fossil fuel burning causes increasing CO 2 by 0.5%/yr l Exacerbates Global Warming l Cf Venus – 700K

LIFE on EARTH l Earth is the only planet known to be harbouring life. l Life arose early on. Fossils date back 3.5 billion years. ä Origin of life is unsure. ä Miller experiment: produced amino acids and other pre-biological molecules from primitive Earth atmosphere - mainly methane, water, ammonia, CO 2, no O 2.

LIFE on EARTH l Development of plants: l Formation of the ozone (O 3 ) layer ä Use up CO 2 and produce O 2 - photosynthesis. ä Free O 2 in atmosphere 2 billion years ago. ä Protects Earth from UV. ä This allowed life to leave protective oceans and colonize the land. Not possible earlier.

COSMIC INFLUENCES on EARTH’S EVOLUTION l Moon is heavily cratered - caused by impacts. ä Where are Earth’s craters? ä Most lost by erosion and geological activity.

COSMIC INFLUENCES on EARTH’S EVOLUTION l More than 150 impact craters are still recognized on Earth’s surface. METEOR CRATER ä 0.1 km meteor ä Crater size = 10 x size of impacting object 1.2 km

COSMIC INFLUENCES on EARTH’S EVOLUTION l More than 150 impact craters are still recognized on Earth’s surface.

COSMIC INFLUENCES on EARTH’S EVOLUTION l Concern is that a large object, ≥10 km, will collide with Earth releasing a few billion times as much energy as Hiroshima bomb.

COSMIC INFLUENCES on EARTH’S EVOLUTION l Concern is that a large object, 10 km, will collide with Earth releasing a few billion times as much energy as Hiroshima bomb. l One such object crosses Earth’s orbit every 100 million years.

ORBITS of the 100 LARGEST KNOWN NEAR-EARTH ASTEROIDS

IMPACT FREQUENCY Impactors on the surface of the space shuttle 1  m, 30  sec Shooting stars 1 mm, 30 sec Meteorites 1m, 1yr Arizona Crater 100 m, 10 4 yr Sudbury, Ontario 10 km, 10 8 yr

COSMIC INFLUENCES on EARTH’S EVOLUTION l More than 150 impact craters are still recognized on Earth’s surface. METEOR CRATER ä 0.1 km meteor ä Crater size = 10 x size of impacting object 1.2 km

TUNGUSKA EVENT Siberia June 30, 1908 Projectile exploded before impacting Earth

Projectile’s mass estimated to be 100,000 tons Caused widespread damage.

TUNGUSKA EVENT

THE SOLAR SYSTEM l Comets can be captured by Jupiter. l Actually orbit Jupiter – orbits unstable. l Comet Shoemaker-Levy9 discovered 1992 l Broke into fragments near “Peri-Jupiter” l Fragments predicted to crash into Jupiter 1994

SHOEMAKER-LEVY9 COMET

IMPACTIMPACT Earth’sViewVoyager’sView

SHOEMAKER-LEVY IMPACT

DEVELOPMENT of DUST CLOUD Impact

IMPACT DUST CLOUDS

IR IMAGE of IMPACTS Io

COSMIC INFLUENCES on EARTH’S EVOLUTION con’t

EFFECTS of a MASSIVE IMPACT

ä Huge tidal waves. ä Dust high up in the atmosphere. ä Block out Sun for about one year, kills photosynthesis. ä World-wide fires, forests and grasslands destroyed. ä Highly acidic rains. ä Animals depending on plants die (dinosaurs?), rise of mammals. ä Global earthquakes.

EXTINCTIONS, the SOLAR SYSTEM and our GALAXY l Past 100 million years many large scale extinctions (~ 10) identified on Earth. äIn these, a significant fraction of existing species were extinguished. l Best known is extinction of the dinosaurs 65 million years ago after flourishing for 100 million years.

EXTINCTIONS, the SOLAR SYSTEM and our GALAXY ä äImpact of ~ 20 km asteroid. ä äEvidence: crater in Gulf of Mexico and Iridium layer. l What caused the extinctions?

EXTINCTIONS, the SOLAR SYSTEM and our GALAXY l What caused the extinctions? ä äImpact of ~ 20 km asteroid. ä äEvidence: crater in Gulf of Mexico and Iridium layer. ä äNearby supernova (depletes O 3, forming NO 2 ). Crab Nebula

EXTINCTION of the DINOSAURS

ALTERNATE DINOSAUR EXTINCTION THEORY

SPIRAL GALAXY

EXTINCTIONS, the SOLAR SYSTEM and our GALAXY l Supernovae and impacts more likely when Sun passes through spiral arm in our Galaxy äOort cloud comets get perturbed.

OORT CLOUD GETS PERTURBED