Chapter 7 Earth and the Terrestrial Worlds

WHAT DO YOU THINK? Why are Venus (too HOT), Mars (too COLD) and Earth (just right!) so different in their atmospheres? Could Mars have supported life long ago? How do we know? Is life known to exist on Mars today?

In this chapter you will discover… Mercury, a Sun-scorched planet with a heavily cratered surface and a substantial iron core Venus, perpetually shrouded in thick, poisonous clouds and mostly covered by gently rolling hills Mars, a red, dusty planet that once had running water on its surface and may still have liquid water underground The role of Carbon Dioxide as a insulator for Planetary climates.

Essay Questions Describe the atmospheres of Venus, Earth, and Mars. Why are these three atmospheres so different? What does the Martian surface tell us about the planet's history, and future?, and its similarities and differences with our Earth. How did the Moon form? How do we know? Describe the composition of the Moon, and its similarities and differences with our Earth. How did the Moon form? How do we know?

Mercury craters smooth plains cliffs

Venus volcanoes few craters Radar view of a twin- peaked volcano

Mars some craters volcanoes riverbeds?

Moon craters smooth plains

Earth volcanoes craters mountains riverbeds

Why have the planets turned out so differently, even though they formed at the same time from the same materials? Why have the planets turned out so differently, even though they formed at the same time from the same materials?

Why is Venus too hot, Mars too cold, and Earth just right?? The Goldilocks Question!

Why is Venus too hot, Mars too cold, and Earth just right?? The Goldilocks Question! Distance? Venus is too close, Mars too far away from the Sun, and Earth just right? Size? Mars too small to retain its heat? Life? Earth’s oceans and life forms tranform the planet?

The Role of Distance? Earth is located at an optimal distance from the Sun for liquid water to exist…

Distance can’t be the only factor! We now know MARS had liquid water, too!

The Role of SIZE? Earth is large enough for internal heat to drive volcanoes and create an atmosphere

SIZE can’t be the only factor! Earth and Venus are almost the same size, and seem identical in composition!

The Role of Atmosphere? Earth is able to recycle CO2 and retain water in its atmosphere…

A Combination of Factors… Earth is habitable because it is: large enough to remain geologically active, at the right distance from Sun so oceans could form, AND able to retain water in the atmosphere to help cycle CO2

The Greenhouse Effect

Greenhouse Gases Any gas that Any gas that absorbs infrared light Greenhouse gas: often molecules with two different types of elements (CO 2, H 2 O, CH 4 ) Greenhouse gas: often molecules with two different types of elements (CO 2, H 2 O, CH 4 ) Not a greenhouse gas: molecules with one or two atoms of the same element (O 2, N 2 ) Not a greenhouse gas: molecules with one or two atoms of the same element (O 2, N 2 )

The Greenhouse Effect on Earth

Greenhouse Effect: Bad? The Earth is much warmer because of the greenhouse effect than it would be without an atmosphere…but so is Venus. How can Earth “regulate” CO 2 ?

Goldilocks & the Earth’s CO2 cycle What does COKE have to do with Astronomy??

Goldilocks & the Earth’s CO2 cycle Carbonation was not initially part of Coke!

Goldilocks & the Earth’s CO2 cycle Carbonation occurs naturally when pushing water with CO2 gas!

Carbon Dioxide Cycle How does our atmosphere & tectonics combine to regulate temperatures? How does life play a role?

Carbon Dioxide Cycle Carbon Dioxide Cycle Step 1: Evaporation/Rain Liquid water evaporates Liquid water evaporates Condenses into clouds in lower atmosphere Condenses into clouds in lower atmosphere Rain falls through atmosphere forming Carbonic Acid (H 2 CO 3) Rain falls through atmosphere forming Carbonic Acid (H 2 CO 3)  CO2 gas is absorbed 1

Carbon Dioxide Cycle Carbon Dioxide Cycle Step 2: Mineral Erosion by Acid Rain Carbonic Acid (H 2 CO 3 ) in rivers erodes rocks Carbonic Acid (H 2 CO 3 ) in rivers erodes rocks Carbonate (CO 3 2- ) ion picked up in minerals washed to ocean Carbonate (CO 3 2- ) ion picked up in minerals washed to ocean Calcium easily absorbed Calcium easily absorbed  CO2 is carried to oceans 2

Carbon Dioxide Cycle Carbon Dioxide Cycle Step 3: Tying Carbon into Rocks & Life! Calcium from rocks forms CaCO 3 (Calcium Carbonate) Calcium from rocks forms CaCO 3 (Calcium Carbonate) CaCO 3 = Limestone CaCO 3 = Limestone CaCO 3 = Coral, Mollusk shells! CaCO 3 = Coral, Mollusk shells! 3  CO2 accumulates on seafloor

Carbon Dioxide Cycle Carbon Dioxide Cycle Step 4: Tectonics & Subduction! Tectonics gradually pulls seafloor down Tectonics gradually pulls seafloor down CaCO 3 broken back into CO2 & other minerals CaCO 3 broken back into CO2 & other minerals 4  CO2 now inside crust

Carbon Dioxide Cycle Carbon Dioxide Cycle Step 5: Volcanic Outgassing! Eventual Volcanic Activity pushes CO2 back into atmosphere Eventual Volcanic Activity pushes CO2 back into atmosphere 5  CO2 now in atmosphere again!

Carbon Dioxide Cycle “Recycle” CO2 from atmosphere to crust to atmosphere over time Estimate ~25 million years or more for this to occur globally

Carbon Dioxide Cycle “Feedback Loop” Suppose evaporation stopped, during an ice age…. What would happen over time?

Carbon Dioxide Cycle Carbon Dioxide Cycle Feedback Loop: Ice Age No evaporation No evaporation No Rain No Rain NO CO2 gas absorbed NO CO2 gas absorbed 1

Carbon Dioxide Cycle Carbon Dioxide Cycle Feedback Loop: Ice Age No evaporation No evaporation No Rain No Rain NO CO2 gas absorbed NO CO2 gas absorbedBut… Tectonic Activity & Volcanoes continue! Tectonic Activity & Volcanoes continue! Gradual CO2 concentration increase! Gradual CO2 concentration increase! 1 5

Carbon Dioxide Cycle Carbon Dioxide Cycle Feedback Loop: Ice Age Tectonic Activity & Volcanoes continue! Gradual CO2 concentration increase! More Greenhouse Effect => warmer! Ice Melts! Cycle restored! 1 5

Long-Term Climate Change Changes in Earth’s axis tilt might lead to ice ages. Changes in Earth’s axis tilt might lead to ice ages. Widespread ice tends to lower global temperatures by increasing Earth’s reflectivity. Widespread ice tends to lower global temperatures by increasing Earth’s reflectivity.

Long-Term Climate Change CO 2 from outgassing will build up if oceans are frozen, ultimately raising global temperatures again.

Carbon Dioxide Cycle “Feedback Loop” Suppose CO2 in our atmosphere traps too much heat, and we heat up? What would happen over time?

Carbon Dioxide Cycle Carbon Dioxide Cycle Feedback Loop: Global Warming Liquid water evaporates FASTER Liquid water evaporates FASTER MORE Rain MORE Rain  MORE CO2 gas is absorbed 1 5

Carbon Dioxide Cycle Carbon Dioxide Cycle Feedback Loop: Global Warming Volcanoes continue at “normal” rate… Gradual CO2 concentration decrease! Less Greenhouse Effect => cooler! Cycle restored! 5 1

Studying other Terrestrial planets teaches us about Earth…

Terrestrial Planet Interiors Applying what we have learned about Earth’s interior to other planets tells us what their interiors are probably like. Applying what we have learned about Earth’s interior to other planets tells us what their interiors are probably like.

Why is Earth geologically active?

Earth’s Interior Core: Highest density; nickel and iron Core: Highest density; nickel and iron Mantle: Moderate density; silicon, oxygen, etc. Mantle: Moderate density; silicon, oxygen, etc. Crust: Lowest density; granite, basalt, etc. Crust: Lowest density; granite, basalt, etc.

Terrestrial Planet Interiors Applying what we have learned about Earth’s interior to other planets tells us what their interiors are probably like. Applying what we have learned about Earth’s interior to other planets tells us what their interiors are probably like.

Why are terrestrial planets layered at all? Why would we have a heavy core, a medium-density mantle, and a light crust? Why (and when?) do mixed compounds separate?

Why do water and oil separate?

A. Water molecules repel oil molecules electrically. B. Water is denser than oil, so oil floats on water. C. Oil is more slippery than water, so it slides to the surface of the water. D. Oil molecules are bigger than the spaces between water molecules.

Why do water and oil separate? A. Water molecules repel oil molecules electrically. B. Water is denser than oil, so oil floats on water. C. Oil is more slippery than water, so it slides to the surface of the water. D. Oil molecules are bigger than the spaces between water molecules.

Differentiation Gravity pulls high- density material to center Gravity pulls high- density material to center Lower-density material floats to surface Lower-density material floats to surface Material ends up separated by density Material ends up separated by density

Thought Question What is necessary for to occur in a planet? What is necessary for differentiation to occur in a planet? A. It must have metal and rock in it. B. It must be a mix of materials of different density. C. Material inside must be able to flow. D. All of the above. E. b and c.

Thought Question What is necessary for differentiation to occur in a planet? A. A. It must have metal and rock in it. B. B. It must be a mix of materials of different density. C. C. Material inside must be able to flow. D. D. All of the above. E. E. b and c.

Lithosphere A planet’s outer layer of cool, rigid rock is called the. A planet’s outer layer of cool, rigid rock is called the lithosphere. It “floats” on the warmer, softer rock that lies beneath. It “floats” on the warmer, softer rock that lies beneath.

Thought Question Do rocks ? Do rocks s-t-r-e-t-c-h? A. No—rock is rigid and cannot deform without breaking. B. Yes—but only if it is molten rock. C. Yes—rock under strain may slowly deform.

Thought Question Do rocks s-t-r-e-t-c-h? A. No—rock is rigid and cannot deform without breaking. B. Yes—but only if it is molten rock. C. C. Yes—rock under strain may slowly deform.

Strength of Rock Rock stretches when pulled slowly but breaks when pulled rapidly. Rock stretches when pulled slowly but breaks when pulled rapidly. The gravity of a large world pulls slowly on its rocky content, shaping the world into a sphere. The gravity of a large world pulls slowly on its rocky content, shaping the world into a sphere.

Heat Drives Geological Activity Convection: hot rock rises, cool rock falls. One convection cycle takes ~100 million years on Earth.

Sources of Internal Heat 1. Gravitational potential energy of accreting planetesimals 2. Differentiation 3. Radioactivity

Heating of Interior over Time Accretion and differentiation when planets were young Accretion and differentiation when planets were young Radioactive decay is most important heat source today Radioactive decay is most important heat source today

Cooling of Interior Convection Conduction Radiation

Cooling of Interior transports heat as hot material rises and cool material falls Convection transports heat as hot material rises and cool material falls Conduction transfers heat from hot material to cool material Conduction transfers heat from hot material to cool material Radiation sends energy into space Radiation sends energy into space

Thought Question What cools off faster? A. A grande-size cup of Starbucks coffee B. A teaspoon of cappuccino in the same cup

Thought Question What cools off faster? A. A grande-size cup of Starbucks coffee B. A teaspoon of cappuccino More surface area, less volume

Thought Question What cools off faster? A. A BIG terrestrial planet B. A tiny terrestrial planet

Thought Question What cools off faster? A. A big terrestrial planet B. A tiny terrestrial planet

Role of Size Smaller worlds cool off faster and harden earlier. Smaller worlds cool off faster and harden earlier. Moon and Mercury are now geologically “dead.” Moon and Mercury are now geologically “dead.”

Planetary Magnetic Fields Moving charged particles create magnetic fields. A planet’s interior can create magnetic fields if - it is electrically conducting, & - it is circulating and/or rotating.

Earth’s Magnetosphere Earth’s magnetic fields protects us from charged particles from the Sun. The charged particles can create aurorae (“Northern lights”).

Thought Question If the planet core is cold, do you expect it to have magnetic fields? A. Yes, refrigerator magnets are cold, and they have magnetic fields. B. No, planetary magnetic fields are generated by moving charges around, and if the core is cold, nothing is moving.

Thought Question If the planet core is cold, do you expect it to have magnetic fields? A. Yes, refrigerator magnets are cold, and they have magnetic fields. B. B. No, planetary magnetic fields are generated by moving charges around, and if the core is cold, nothing is moving.

How do we know what’s inside a planet? P waves push matter back and forth. P waves push matter back and forth. S waves shake matter side to side. S waves shake matter side to side.

How do we know what’s inside a planet? P waves go through Earth’s core, but S waves do not. P waves go through Earth’s core, but S waves do not. We conclude that Earth’s core must have a liquid outer layer. We conclude that Earth’s core must have a liquid outer layer.

What processes shape Earth’s surface?

Geological Processes Impact cratering — Impacts by asteroids or comets Volcanism — Eruption of molten rock onto surface Tectonics — Disruption of surface by internal stresses Erosion — Changes made by wind, water, or ice

Impact Craters Meteor Crater (Arizona) Tycho (Moon)

Impact Cratering Most cratering happened soon after the solar system formed. Most cratering happened soon after the solar system formed. Craters are about 10 times wider than objects that made them. Craters are about 10 times wider than objects that made them. Small craters greatly outnumber large ones. Small craters greatly outnumber large ones. The Production of a Crater

Volcanism Molten rock (magma) finds a path through crust (lithosphere) to surface. Molten rock (magma) finds a path through crust (lithosphere) to surface. Molten rock is called lava after it reaches the surface. Molten rock is called lava after it reaches the surface.

Lava and Volcanoes Runny lava makes flat lava plains. Slightly thicker lava makes broad shield volcanoes. Thickest lava makes steep stratovolcanoes.

Outgassing Volcanism also releases gases from Earth’s interior into the atmosphere. Volcanism also releases gases from Earth’s interior into the atmosphere.

Tectonics Convection of the mantle creates stresses in the crust called tectonic forces. Convection of the mantle creates stresses in the crust called tectonic forces.

Tectonics Compression forces make mountains. Compression forces make mountains. Valleys form where crust is pulled apart. Valleys form where crust is pulled apart.

Erosion Weather-driven processes that break down or transport rock: Water Water Ice Ice Wind Wind Debris Movement Debris Movement

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

Erosion by Ice Glaciers carved the Yosemite Valley. Glaciers carved the Yosemite Valley.

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

Erosional Debris Erosion can create new features by depositing debris. Erosion can create new features by depositing debris.

Planetary Destiny Earth is habitable because it is large enough to remain geologically active, and it is at the right distance from the Sun so oceans could form.

How does Earth’s atmosphere affect the planet ?

Effects of Atmosphere on Earth 1. Erosion 2. Makes the sky blue! 3. Radiation protection 4. Greenhouse effect

Thought Question Why is the sky blue? Why is the sky blue? A. The sky reflects light from the oceans. B. Oxygen atoms are blue. C. Nitrogen atoms are blue. D. Air molecules scatter blue light more than red light. E. Air molecules absorb red light.

Thought Question Why is the sky blue? Why is the sky blue? A. The sky reflects light from the oceans. B. Oxygen atoms are blue. C. Nitrogen atoms are blue. D. D. Air molecules scatter blue light more than red light. E. Air molecules absorb red light.

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

Earth’s atmosphere absorbs light at most wavelengths.

Radiation Protection All X-ray light is absorbed very high in the atmosphere. All X-ray light is absorbed very high in the atmosphere. Ultraviolet light is absorbed by ozone (O 3 ) ~ 30 miles high Ultraviolet light is absorbed by ozone (O 3 ) ~ 30 miles high

Earth as a “Living” Planet What unique features on Earth are important for human life? What unique features on Earth are important for human life? How is human activity changing our planet? How is human activity changing our planet? What makes a planet habitable? What makes a planet habitable?

What unique features of Earth are important for life? 1. Surface liquid water 2. Atmospheric oxygen 3. Plate tectonics 4. Climate stability

What unique features of Earth are important to human life? 1. Surface liquid water 2. Atmospheric oxygen Plate tectonics Climate stability Earth’s distance from the Sun and moderate greenhouse effect make liquid water possible.

What unique features of Earth are important to human life? 1. Surface liquid water 2. Atmospheric oxygen 3. Plate tectonics 4. Climate stability PHOTOSYNTHESIS (plant life) is required to make high concentrations of O 2, which also produces the protective layer of O 3.

What unique features of Earth are important to human life? 1. Surface liquid water 2. Atmospheric oxygen 3. Plate tectonics 4. Climate stability Plate tectonics are an important step in the carbon dioxide cycle.

Continental Motion Idea of continental drift was inspired by puzzle-like fit of continents Idea of continental drift was inspired by puzzle-like fit of continents Mantle material erupts where seafloor spreads Mantle material erupts where seafloor spreads

Plate Motions

Continental Motion Motion of continents can be measured with GPS Motion of continents can be measured with GPS

Tectonics & Seafloor Recycling Seafloor is recycled through a process known as subduction Seafloor is recycled through a process known as subduction

What unique features of Earth are important to human life? 1. Surface liquid water 2. Atmospheric oxygen 3. Plate tectonics 4. Climate stability The CO 2 cycle acts like a thermostat for Earth’s temperature.

These unique features are intertwined: Plate tectonics create climate stability Plate tectonics create climate stability Climate stability allows liquid water Climate stability allows liquid water Liquid water is necessary for life Liquid water is necessary for life Life is necessary for atmospheric oxygen Life is necessary for atmospheric oxygen How many other connections between these can you think of?

How is human activity changing our planet?

Dangers of Human Activity Human-made CFCs in the atmosphere destroy ozone, reducing protection from UV radiation. Human-made CFCs in the atmosphere destroy ozone, reducing protection from UV radiation. Human activity is driving many other species to extinction. Human activity is driving many other species to extinction. Human use of fossil fuels produces greenhouse gases that can cause global warming. Human use of fossil fuels produces greenhouse gases that can cause global warming.

Global Climate Change Earth’s average temperature has increased by 0.5°C in the past 50 years. Earth’s average temperature has increased by 0.5°C in the past 50 years. The concentration of CO 2 is rising rapidly. The concentration of CO 2 is rising rapidly. An unchecked rise in greenhouse gases is leading to global climate change. An unchecked rise in greenhouse gases is leading to global climate change.

CO 2 Concentration Global temperatures have tracked CO 2 concentration for the last 500,000 years. Global temperatures have tracked CO 2 concentration for the last 500,000 years. Antarctic air bubbles indicate the current CO 2 concentration is at its highest level in at least 500,000 years. Antarctic air bubbles indicate the current CO 2 concentration is at its highest level in at least 500,000 years.

CO 2 Concentration Most of the CO 2 increase has happened in last 50 years!

Modeling of Climate Change Build climate models based on current/past data Build climate models based on current/past data Models suggest recent temperature increase is consistent with human production of greenhouse gases. Models suggest recent temperature increase is consistent with human production of greenhouse gases.

What makes a planet habitable? Located at an optimal distance from the Sun for liquid water to exist

What makes a planet habitable? Large enough for geological activity to release and retain water and atmosphere

Planetary Destiny Earth is habitable because it is large enough to remain geologically active, and it is at the right distance from the Sun so oceans could form.

Planetary Destiny Earth is habitable because it is large enough to remain geologically active, and it is at the right distance from the Sun so oceans could form.