The Terrestrial Planets

Final Exam Essay Question Describe the atmospheres of Venus, Earth, and Mars. Why are these three atmospheres so different?

Venus’ surface Lots of volcanoes Relatively few craters

Venus’ atmosphere Huge amounts of CO2 Thick Sulfuric Acid H2SO4 Clouds

Mars’ surface some craters volcanoes riverbeds

Mars’ atmosphere very thin mostly CO2

Earth’ surface volcanoes craters mountains riverbeds oceans

Earth’ atmosphere Nitrogen & Oxygen little CO2

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

What processes shape all terrestrial planetary surfaces?

Shared Geological Processes Impact cratering Impacts by asteroids or comets Meteor Crater (Arizona) Tycho (Moon)

Shared Geological Processes Impact cratering Impacts by asteroids or comets Volcanism Eruption of molten rock onto surface

Volcanism Molten rock (magma) finds path through crust to surface. Molten rock called lava as it reaches the surface. Release huge amounts of gas into atmosphere

Outgassing No, not from cows…

Outgassing from Volcanoes! Volcanism also releases gases from planet’s interior into the atmosphere.

Shared Geological Processes Impact cratering Impacts by asteroids or comets Volcanism Eruption of molten rock onto surface Tectonics Disruption of surface by internal stresses

Shared 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

Erosion Weather-driven processes that break down or transport rock. Water/Ice movement by glaciers & rivers Atmospheric Movement by wind, storms Cyclic heating/cooling

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

The Goldilocks Problem?

The Goldilocks Problem? Astronomical!

Why is Venus so hot…

and Mars so cold… FIGURE 7-18 Mars This photograph, taken from space, shows the Arabia Terra (in light orange) and carbon dioxide snow at the planet’s poles. (NASA, The Hubble Heritage Team)

and Earth just right….? FIGURE 7-18 Mars This photograph, taken from space, shows the Arabia Terra (in light orange) and carbon dioxide snow at the planet’s poles. (NASA, The Hubble Heritage Team)

Thought Question What is the main reason why Venus is hotter than Earth? Venus is closer to the Sun than Earth. Venus is more reflective than Earth. Venus is less reflective than Earth. Rain stopped, but volcanoes didn’t Human activity

# 1 Answer given by most people… and it’s not correct! Thought Question What is the main reason why Venus is hotter than Earth? Venus is closer to the Sun than Earth. # 1 Answer given by most people… and it’s not correct!

Thought Question What is the main reason why Venus is hotter than Earth? Venus is closer to the Sun than Earth. Venus is more reflective than Earth. Venus is less reflective than Earth. Rain stopped, but volcanoes didn’t Human activity

Thought Question What is the main reason why Mars is no longer considered habitable (on its surface) Mars is farther from the Sun than Earth, and too cold Mars doesn’t have a thick atmosphere Mars’ volcanoes stopped erupting The greenhouse effect is not as strong on Mars compared to Earth. Martians screwed up the climate long ago.

# 1 Answer given by most people… and it’s not correct! Thought Question What is the main reason why Mars is no longer considered habitable (on its surface) Mars is farther from the Sun than Earth, and too cold # 1 Answer given by most people… and it’s not correct!

Thought Question What is the main reason why Mars is no longer considered habitable (on its surface) Mars is farther from the Sun than Earth, and too cold Mars doesn’t have a thick atmosphere Mars’ volcanoes stopped erupting The greenhouse effect is not as strong on Mars compared to Earth. Martians screwed up the climate long ago.

Why is Venus too hot, Mars too cold, and Earth just right?? 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 & life forms transform 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 & outgas an atmosphere

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

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

The Role of Atmosphere? Is it the Greenhouse Effect? The Earth IS much warmer because of the greenhouse effect than it would be without an atmosphere… …but so is Venus.

The Greenhouse Effect on Earth FIGURE 6-4 The Greenhouse Effect (a) Sunlight and heat from Earth’s interior warm Earth’s surface, which in turn radiates energy, mostly as infrared radiation. Much of this radiation is absorbed by atmospheric carbon dioxide and water, heating the air, which in turn raises Earth’s temperature even further. In equilibrium, Earth radiates as much energy as it receives.

Explaining Goldilocks! A Combination of Factors… Earth is “just right” – 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

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

Greenhouse Effect: Bad? The Earth IS much warmer because of the greenhouse effect than it would be without an atmosphere… But how can Earth “regulate” CO2 ?

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 Step 1: Evaporation/Rain Liquid water evaporates Condenses into clouds in lower atmosphere Rain falls through atmosphere forming Carbonic Acid (H2CO3)  CO2 gas is absorbed 1

Carbon Dioxide Cycle Step 2: Mineral Erosion by Acid Rain Carbonic Acid (H2CO3) in rivers erodes rocks Carbonate (CO32-) ion picked up in minerals washed to ocean Calcium easily absorbed  CO2 is carried to oceans 2

Carbon Dioxide Cycle Step 3: Tying Carbon into Rocks & Life! Calcium from rocks forms CaCO3 (Calcium Carbonate) CaCO3 = Limestone CaCO3 = Coral, Mollusk shells! 3  CO2 accumulates on seafloor

Carbon Dioxide Cycle Step 4: Tectonics & Subduction! Tectonics gradually pulls seafloor down CaCO3 broken back into CO2 & other minerals 4  CO2 now inside crust

Carbon Dioxide Cycle Step 5: Volcanic Outgassing! 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 Feedback Loop: Ice Age No evaporation No Rain NO CO2 gas absorbed 1

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

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. Widespread ice tends to lower global temperatures by increasing Earth’s reflectivity.

Long-Term Climate Change CO2 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 Feedback Loop: Global Warming Liquid water evaporates FASTER MORE Rain  MORE CO2 gas is absorbed 1 5

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

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

What unique features of Earth are important for life? Surface liquid water Atmospheric oxygen Plate tectonics Climate stability

What unique features of Earth are important to human life? Surface liquid water 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? Surface liquid water Atmospheric oxygen Plate tectonics Climate stability PHOTOSYNTHESIS (plant life) is required to make high concentrations of O2, which also produces the protective layer of O3.

What unique features of Earth are important to human life? Surface liquid water Atmospheric oxygen Plate tectonics 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 Mantle material erupts where seafloor spreads

Plate Motions

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

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

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

Carbon Dioxide Cycle Step 1: Evaporation/Rain Liquid water evaporates Condenses into clouds in lower atmosphere Rain falls through atmosphere forming Carbonic Acid (H2CO3)  CO2 gas is absorbed 1

Carbon Dioxide Cycle Step 2: Mineral Erosion by Acid Rain Carbonic Acid (H2CO3) in rivers erodes rocks Carbonate (CO32-) ion picked up in minerals washed to ocean Calcium easily absorbed  CO2 is carried to oceans 2

Carbon Dioxide Cycle Step 3: Tying Carbon into Rocks & Life! Calcium from rocks forms CaCO3 (Calcium Carbonate) CaCO3 = Limestone CaCO3 = Coral, Mollusk shells! 3  CO2 accumulates on seafloor

Carbon Dioxide Cycle Step 4: Tectonics & Subduction! Tectonics gradually pulls seafloor down CaCO3 broken back into CO2 & other minerals 4  CO2 now inside crust

Carbon Dioxide Cycle Step 5: Volcanic Outgassing! 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 Venus Feedback Loop Failure Too Hot for clouds to form low enough But… Volcanoes don’t stop! 1 5

Carbon Dioxide Cycle Venus Feedback Loop Failure No Rain NO CO2 gas absorbed More CO2 added! Runaway Greenhouse Effect! 1

Carbon Dioxide Cycle Mars Feedback Loop Failure Evaporation Rain CO2 gas flushed out But… Interior cools off Volcanoes Stop! 1 5

Carbon Dioxide Cycle Mars Feedback Loop Failure Atmosphere CO2 decreases Planet freezes 1 5

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

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

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

Carbon Dioxide Cycle Earth 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. Widespread ice tends to lower global temperatures by increasing Earth’s reflectivity….

Long-Term Climate Change But…. from CO2 feedback cycle CO2 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 Earth Feedback Loop: Global Warming Liquid water evaporates FASTER MORE Rain  MORE CO2 gas is absorbed 1 5

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

What unique features of Earth are important to human life? Surface liquid water Atmospheric oxygen Plate tectonics Climate stability The CO2 cycle acts like a thermostat for Earth’s temperature.

These unique features are intertwined: Plate tectonics create climate stability Climate stability allows liquid water Liquid water is necessary for life Life is necessary for atmospheric oxygen For example: atmospheric oxygen allows life on land Stable climate good for life Water may enable plate tectonics 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 activity is driving many other species to extinction. 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. The concentration of CO2 is rising rapidly. An unchecked rise in greenhouse gases is leading to global climate change.

CO2 Concentration Global temperatures have tracked CO2 concentration for the last 500,000 years. Antarctic air bubbles indicate the current CO2 concentration is at its highest level in at least 500,000 years.

Most of the CO2 increase has happened in last 50 years! CO2 Concentration Most of the CO2 increase has happened in last 50 years!

Modeling of Climate Change Build climate models based on current/past data 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.