Homework #4  Due Wednesday, February 24, 11:59PM  Covers Chapters 6 and 7  Estimated time to complete: 1 hour  Read chapters, review notes before starting  Due Wednesday, February 24, 11:59PM  Covers Chapters 6 and 7  Estimated time to complete: 1 hour  Read chapters, review notes before starting

Telescope Viewing Tonight! Come see Jupiter and its moons through the Gallalee Hall 16” Telescope tonight from 7-10 PM. From this classroom, go right down the hall, turn right and find stairwell. Go up two flights of stairs and to the left to get out to the roof (4 th floor). Be sure to sign the sign-up sheet to receive an extra days worth of clicker credit.

Can Rock Flow?  Rock stretches when pulled slowly (especially when very warm) but breaks when pulled rapidly.  The gravity of a large world pulls slowly on its rocky content, shaping the world into a sphere.  Bodies over 500 km in diameter will become spherical in ~1 billion years by slow, slow deformation of rock by gravity.  Rock stretches when pulled slowly (especially when very warm) but breaks when pulled rapidly.  The gravity of a large world pulls slowly on its rocky content, shaping the world into a sphere.  Bodies over 500 km in diameter will become spherical in ~1 billion years by slow, slow deformation of rock by gravity.

Lithosphere  A planet’s outer layer of cool, rigid rock is called the lithosphere (crust + upper part of mantle).  Rock in lithosphere is cold and does not deform like silly putty, while warmer mantle rock below it does deform.  Rigid lithosphere “floats” on the warmer, softer rock that lies beneath.  A planet’s outer layer of cool, rigid rock is called the lithosphere (crust + upper part of mantle).  Rock in lithosphere is cold and does not deform like silly putty, while warmer mantle rock below it does deform.  Rigid lithosphere “floats” on the warmer, softer rock that lies beneath. Lithosphere can be broken into plates.

Heat Drives Geological Activity  Rock heated by radioactivity in core.  Heat moved through mantle by convection.  Convection: Hot rock rises, cool rock falls.  One convection cycle takes 100 million years on Earth.  Rock heated by radioactivity in core.  Heat moved through mantle by convection.  Convection: Hot rock rises, cool rock falls.  One convection cycle takes 100 million years on Earth. Rock actually “flows” from inner mantle to outer mantle and back! Hard, rigid lithosphere rock does not circulate

Why Does Lack of Heat Matter?  Once the internal heat is gone, the once-soft hot rock cools off  lithosphere grows thicker and thicker.  Cold rock will not flow and rise to the surface through cracks in the lithosphere  no more geological activity such as volcanoes  Once the internal heat is gone, the once-soft hot rock cools off  lithosphere grows thicker and thicker.  Cold rock will not flow and rise to the surface through cracks in the lithosphere  no more geological activity such as volcanoes This is what has already happened on Mercury and the Moon long ago, and is happening to Mars now.

Role of Size  Smaller worlds cool off faster and solidify earlier.  The Moon and Mercury are now geologically “dead” because they have already lost all their internal heat.  Smaller worlds cool off faster and solidify earlier.  The Moon and Mercury are now geologically “dead” because they have already lost all their internal heat. Since internal heat drives geological activity, a total loss of heat leads to a total loss of geological activity. Important!

Surface Area–to–Volume Ratio  Heat content depends on volume.  Loss of heat through radiation depends on surface area.  Cooling rate depends on surface area divided by volume:  Heat content depends on volume.  Loss of heat through radiation depends on surface area.  Cooling rate depends on surface area divided by volume: 3 Surface area–to–volume ratio= 4  r 2 4  r 3  3 r Easy to remember: a hot pea cools off much faster than a hot potato at the same initial temperature Bigger objects cool more slowly

What key quality is responsible for the Moon and Mercury being geologically dead? A) their distance from the Sun B) their chemical composition C) their size D) their lack of atmosphere

What key quality is responsible for the Moon and Mercury being geologically dead? A) their distance from the Sun B) their chemical composition C) their size D) their lack of atmosphere Because of their small size, they have higher surface area-to-volume ratios  cooled off faster (think hot pea vs. hot baked potato)

What processes shape planetary surfaces?

Processes That Shape Surfaces  Impact cratering  Impacts by asteroids or comets  Volcanism  Eruption of molten rock onto surface  Tectonics  Disruption of a planet’s surface by internal stresses  Erosion  Surface changes made by wind, water, or ice Last 3 processes stop once the internal heat is gone.  Impact cratering  Impacts by asteroids or comets  Volcanism  Eruption of molten rock onto surface  Tectonics  Disruption of a planet’s surface by internal stresses  Erosion  Surface changes made by wind, water, or ice Last 3 processes stop once the internal heat is gone.

Impact Cratering  Most cratering happened soon after the solar system formed (“Period of Heavy Bombardment”).  Craters are about 10 times wider than object that made them, and 10-20% as deep as they are wide (impact at 40, ,000 km/hr).  Small craters greatly outnumber large ones.  Most cratering happened soon after the solar system formed (“Period of Heavy Bombardment”).  Craters are about 10 times wider than object that made them, and 10-20% as deep as they are wide (impact at 40, ,000 km/hr).  Small craters greatly outnumber large ones.

Impact Craters Meteor Crater (Arizona) Tycho Crater (Moon) (Note central rebound peak)

Volcanism  Volcanism happens when molten rock (magma) finds a path through crack in the lithosphere to the surface.  Molten rock is called lava after it reaches the surface.  Volcanism happens when molten rock (magma) finds a path through crack in the lithosphere to the surface.  Molten rock is called lava after it reaches the surface.

Outgassing  Volcanism also releases gases from Earth’s interior into the atmosphere (outgassing). This is where the terrestrial planets got their atmospheres.  key  Atmospheres diffuse away if not continuously replenished  explains lack of atmospheres on dead planets  Volcanism also releases gases from Earth’s interior into the atmosphere (outgassing). This is where the terrestrial planets got their atmospheres.  key  Atmospheres diffuse away if not continuously replenished  explains lack of atmospheres on dead planets Volcano National Park Mount St. Helen’s

Tectonics  Convection of the mantle creates stresses in the crust called tectonic forces.  Compression of crust creates mountain ranges.  Valley can form where crust is pulled apart.  Convection of the mantle creates stresses in the crust called tectonic forces.  Compression of crust creates mountain ranges.  Valley can form where crust is pulled apart.

Plate Tectonics on Earth  Earth’s continents slide around on separate plates of crust.  Lithosphere is fractured into more than a dozen plates  continents sit on some of these plates  Apparently unique to Earth in the Solar System today.  Earth’s continents slide around on separate plates of crust.  Lithosphere is fractured into more than a dozen plates  continents sit on some of these plates  Apparently unique to Earth in the Solar System today.

Continental Motion  The idea of continental drift was inspired by the puzzle-like fit of the continents.  Mantle material erupts where the seafloor spreads, causing plates to slowly drift across the globe.  The idea of continental drift was inspired by the puzzle-like fit of the continents.  Mantle material erupts where the seafloor spreads, causing plates to slowly drift across the globe.

Continental Motion  Motion of the continents (on the pates) can be measured with GPS – few centimeters/year. Plates are pieces of Earth’s fractured lithospher e

Surface Features  The Himalayas formed from a collision between plates.

Surface Features  The Red Sea is formed where plates are pulling apart.

Rifts, Faults, Earthquakes  The San Andreas fault in California is a plate boundary.  Sideways motion of plates can cause earthquakes.  The San Andreas fault in California is a plate boundary.  Sideways motion of plates can cause earthquakes. In 20 million years, SF and LA will be near each other.

Plate Motions  Measurements of plate motions tell us past and future layout of the continents. Rodinia – 750 million year agoPangaea – 250 million years ago

Cryolophosaurus ellioti found in Antarctica

Erosion  Erosion is a blanket term for weather-driven processes that break down or transport rock.  Processes that cause erosion include:  glaciers  rivers  Wind All dependent on the presence of an atmosphere.  Erosion is a blanket term for weather-driven processes that break down or transport rock.  Processes that cause erosion include:  glaciers  rivers  Wind All dependent on the presence of an atmosphere.

Erosion by Ice  Glaciers carved the Yosemite Valley.

Erosion by Water  The Colorado River continues to carve Grand Canyon.

Erosion by Wind  Wind wears away rock and builds up sand dunes.

Erosional Debris  Erosion can create new features such as deltas by depositing debris.  Sediment is transformed onto sedimentary rock – most common type of rock on Earth  Erosion can create new features such as deltas by depositing debris.  Sediment is transformed onto sedimentary rock – most common type of rock on Earth Erosion also builds, not always destroys

Which of the following is the only process capable of shaping the surface of a dead world? A) volcanic activity B) plate tectonics C) erosion D) impact cratering

Which of the following is the only process capable of shaping the surface of a dead world? A) volcanic activity B) plate tectonics C) erosion D) impact cratering First three depend (ultimately) on internal heat.

What is an atmosphere? An atmosphere is a layer of gas that surrounds a world. Source: outgassing from volcanic activity

Earth’s Atmosphere  About 10 kilometers thick  Analogy: as thick as a dollar bill wrapped around a standard globe.  Consists of: Nitrogen: 77% Oxygen: 21% Argon: 1% H 2 O, CO 2 : trace  About 10 kilometers thick  Analogy: as thick as a dollar bill wrapped around a standard globe.  Consists of: Nitrogen: 77% Oxygen: 21% Argon: 1% H 2 O, CO 2 : trace

Effects of Atmosphere on Earth 1) Erosion - rain, wind, ice shapes surface 2) Radiation protection - harmful X-rays, gamma-rays blocked 3) Greenhouse effect - keeps Earth warm (too warm?) 4) Makes the sky blue! 1) Erosion - rain, wind, ice shapes surface 2) Radiation protection - harmful X-rays, gamma-rays blocked 3) Greenhouse effect - keeps Earth warm (too warm?) 4) Makes the sky blue!

Radiation Protection  All X-ray light is absorbed very high in the atmosphere.  Ultraviolet light is absorbed by ozone (O 3 ) – explains concern about holes in the ozone.  All X-ray light is absorbed very high in the atmosphere.  Ultraviolet light is absorbed by ozone (O 3 ) – explains concern about holes in the ozone.

The Greenhouse Effect  Visible (yellow) light passes through the atmosphere easily and warms a planet’s surface.  Planet absorbs optical light and emits thermal blackbody infrared (red) radiation.  The atmosphere absorbs infrared radiation from the surface, trapping heat like a blanket.

Greenhouse effect: Certain molecules let sunlight through but trap escaping infrared photons. (H 2 O, CO 2, CH 4 )  greenhouse gases The Greenhouse Effect

Greenhouse Effect: Good or Bad? Because of the greenhouse effect, Earth is considerably warmer than it would be without an atmosphere (above the freezing point of water)…but so is Venus. Without the greenhouse effect, Earth would be too cold for liquid water to exist on its surface  very bad for life! Because of the greenhouse effect, Earth is considerably warmer than it would be without an atmosphere (above the freezing point of water)…but so is Venus. Without the greenhouse effect, Earth would be too cold for liquid water to exist on its surface  very bad for life!

Why the sky is blue  Atmosphere scatters blue light from the Sun, making it appear to come from different directions.  Sunsets are red because less of the red light from the Sun is scattered.  Atmosphere scatters blue light from the Sun, making it appear to come from different directions.  Sunsets are red because less of the red light from the Sun is scattered.