EARTH OUR HOME IN SPACE

Standards Understand the scale and contents of the universe Explain plate tectonics and understand the evidence that supports it

Earth is best studied terrestrial planet We can draw on our knowledge of Earth to aid us in our understanding of other planets

Earth Data

Formation of Earth Earth formed out of solar nebula Formed at same time as other planets (4.6 billion years ago) Started out as rocky ball of uniform composition and density

Earth began to heat & melt 3 sources of heat: 1. gravitational collapse 2. radioactive decay 3. bombardment by meteorites

Differentiation occurs Differentiation is the formation of layers. Heavier elements sank to middle of molten Earth. Lighter elements floated on top.

Layers of Earth (compositional) Earth is composed of three main layers, defined by what they are made of: Core Mantle Crust

Core Made of iron & nickel Inner core: solid – hot, but too much pressure to be in liquid state. 1255 km thick. Outer core: liquid – rotates around inner core (rotation causes magnetic field). 2220 km thick.

Mantle Region surrounding core Makes up bulk of Earth 2900 km thick Composed of peridotite (rock containing iron and magnesium) Solid that flows (plastic)

Crust Thin, outer layer of Earth Solid Two types: Oceanic crust – thinner than continental crust. Made of basalt (volcanic rock). 7 – 10 km thick. 2. Continental crust – made of granite. 20 – 70 km thick.

Other Layers (mechanical) Defined by how they behave Lithosphere – layer which includes crust and uppermost mantle. Asthenosphere – part of mantle directly below lithosphere.

How do we know layers of Earth? Drilling has only been done to a few km depth (still in crust) Structure known because of seismic waves.

Seismic Waves Vibrations that travel through Earth. Produced by earthquakes or explosions on surface. Waves refract (or bend) at boundaries between layers (because layers composed of rocks of different densities).

2 types of seismic waves Surface waves – travel on surface – not good for studying interior. Body waves – travel through Earth. 2 types: 1. primary or P waves 2. secondary or S waves

Primary or P Waves 1st to arrive at seismic station. Compressional wave. Can travel through solids & liquids.

Secondary or S Wave Arrive after P waves Shear wave Can travel through solids, but not liquid. Don’t travel through outer core  outer core is liquid

S Wave Shadow Zone Zone in which no S waves are recorded by seismic stations.

Plate Tectonics Lithosphere is broken up into segments (tectonic plates) that move upon the partially molten mantle – called Plate Tectonics. Movement of plates responsible for many of Earth’s processes and features, such as mountains, volcanoes and earthquakes. Movement recycles oceanic crust (crust is created and destroyed).

Tectonic Plate Map

Types of Plate Boundaries Plates move relative to each other along one of three types of boundaries Convergent boundary Divergent boundary Transform boundary

Convergent Boundary Where two plates collide. 3 Types: oceanic-continental oceanic crust is more dense and sinks beneath continental crust. Called subduction zone. Where crust is destroyed. Cause volcanoes and earthquakes.

Mt. St. Helens

Convergent Boundary 2. Continental-continental both crusts of same density, so neither sinks. Push together and cause mountain building. Ex: Himalayan Mountains

Himalayas

Convergent Boundary 3. Oceanic – oceanic: older oceanic crust is cooler and denser, so the older of the two crusts is subducted. Forms island arcs, which are volcanically active. Ex: Soufriere Hills Volcano, Montserrat (island in the West Indies)

Soufriere Hills, Montserrat, West Indies

Divergent Boundary Where two plates pull apart. This is where new crust is made. Associated with volcanoes and earthquakes Exs: Mid-ocean ridges Rio Grande Rift (formed Albuquerque Volcanoes).

Iceland: Mid-Atlantic Ridge at Surface and Icelandic Volcano

Transform Boundary Where two plates slide past each other. Causes earthquakes Ex: San Andreas Fault

San Andreas Fault Nimitz Freeway collapse during 1989 Loma Prieta earthquake

What Drives Plate Motion? Convection in Earth’s mantle – hot material rises & cool material sinks What other body in the solar system has convection? The sun

Other Parts of Earth Hydrosphere Atmosphere Magnetosphere

Hydrosphere Includes all the water on Earth that is contained in the oceans, glaciers, streams, lakes, soil, groundwater & air. The oceans comprise 70% of Earth’s total surface area Water moves between these different locations through a process called the hydrologic cycle

Earth’s Atmosphere Air above Earth’s surface. Breathable by humans Mixture of gases: 78% nitrogen 21% oxygen Trace amounts of argon, carbon dioxide & water vapor Large amount of oxygen makes Earth’s atmosphere unique in solar system.

Structure of Atmosphere Troposphere – region where convection (and weather) occurs. Up to ~12 km in altitude. Stratosphere – contains ozone layer Mesosphere – where meteorites burn up Thermosphere – topmost layer, above ~80 km. Where aurorae occur.

Layers of Atmosphere

Origin of Earth’s Atmosphere Atmosphere of early Earth made up of gases most common in solar system (hydrogen, helium, methane, ammonia & water vapor) Escaped into space

Origin of Earth’s Atmosphere Secondary atmosphere was outgassed (expelled) from planet’s interior by volcanoes Surface temperature fell and water vapor condensed, forming oceans Water in oceans also provided by comets impacting Earth Life appeared in oceans and began to produce oxygen Oxygen in present-day atmosphere is direct consequence of evolution of life on Earth.

The Magnetosphere Zone of charged particles at high altitude, trapped by magnetic field. Completely surrounds planet Magnetic N & S poles: where magnetic field lines intersect Earth’s surface. Aligned with axis. Protects Earth from solar particles. Auroras occur when solar wind interacts with magnetosphere

Life Earth is the only known planet to contain life, and it contains lots of it