Planet Earth

How old is the Earth?

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1. 140 million years

2. 500 million years

3. 1 billion years

4. 4.6 billion years

5. 13 billion years

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The Early History of the Earth

Earth formed 4.6 billion years ago from the inner solar nebula.

Four main stages of evolution:

What is “differentiation”?

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1. The mixing of substances.2. Lighter substances sinking to

the bottom, while heavier substances rise to the top.

3. Heavier substances sinking to the bottom, while lighter substances rise to the top.

4. The chemical change of substances near the surface of a planet due to chemical reactions with the atmosphere.

5. The chemical change of substances near the core of a planet induced by great heat.

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The Early History of the Earth

Earth formed 4.6 billion years ago from the inner solar nebula.

Four main stages of evolution:

Two sources of heat in Earth’s interior:

• Potential energy of infalling material

• Decay of radioactive material

Most traces of bombardment (impact craters) now destroyed

by later geological activity

What killed the dinosaurs (according to the most

widely accepted theory)?

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1. Global climate change caused by variations in the sun’s energy output.

2. Global climate change caused by a massive meteorite/comet impact.

3. A reptile dysfunction.4. A nearby stellar explosion

(supernova / gamma-ray burst).

5. Nothing. They still exist (see, e.g., Jurassic Park)!

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Meteorite Impacts on EarthOver 150 impact craters found on Earth.

Most famous example:

Barringer Crater near Flagstaff, AZ:

Impact Craters on EarthBarringer Crater: ~ 1.2 km diameter; 200 m deep

Formed ~ 50,000 years ago by a meteorite of ~ 80 – 100 m diameter

The Chicxulub Crater

This impact may have caused major climate

change, leading to the extinction of many species, including dinosaurs

.

Much larger impact features exist on Earth:

Impact of a large body (comet nucleus?) formed a crater ~ 180 – 300 km in diameter in the Yucatán

peninsula, ~ 65 million years ago:

Seismic waves are bent or bounce off transitions

between different materials or different

densities or temperatures.

Earth’s InteriorDirect exploration of Earth’s interior (e.g.

drilling) is impossible.

Earth’s interior can be explored through

seismology:

Earth quakes produce

seismic waves.

If you are standing next to railroad tracks and you don’t see or hear a train, you can tell if there’s a train approaching by

putting your ear on the tracks. This works because …

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1. your visual abilities improves when you block one of your ears.

2. sound waves travel more rapidly along the tracks than through the air.

3. Sound waves get less absorbed when traveling along the tracks than through the air.

4. All of the above.5. 2. and 3.

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Earth’s Interior (II)

Earth’s interior gets hotter towards the center.

Earth’s core is as hot as the sun’s surface;

metals are liquid near the core.

Basic structure:

Solid crust (light [Si-based] materials)

Solid mantle (light elements, iron-poor)

Liquid core (iron-rich)

Solid inner core (iron-rich)

Earth’s Magnetic Field

Convective motions and rotation of the core generate a

dipole magnetic field

Earth’s core consists mostly of iron + nickel

(materials that magnets are made

out of)

The Role of Earth’s Magnetic FieldEarth’s magnetic field protects Earth from high-energy

particles coming from the sun (solar wind).

Surface of first interaction of solar wind with Earth’s magnetic field =

Bow shock

Region where Earth’s magnetic field dominates = magnetosphere

Some high-energy particles leak through the magnetic field and produce a belt of high-energy particles around Earth: The Van Allen belts

Which phenomenon is caused by the interaction of energetic particles from the

sun with Earth’s magnetosphere?

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1. Northern lights (aurora borealis).

2. Sun spots.

3. Prominences.

4. Hurricanes.

5. Earthquakes.

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The Aurora (Polar Light)

As high-energy particles leak into the lower magnetosphere, they excite molecules near the Earth’s magnetic poles, causing the

Aurora

Tectonic PlatesEarth’s crust is composed of several distinct tectonic plates, which are

in constant motion with respect to each other → Plate tectonics

Tectonic Plates (II)

Evidence for plate tectonics can be found on the ocean floor

… and in geologically active regions all around the Pacific

Geological activity around the Pacific

Volcanism: Mt. St. Helen

Earthquakes: Kobe (Japan)

Volcanism: Pinatubo (Philippines)

Earthquakes: San Francisco

The major Tsunami of 2004 in the Indian Ocean was caused by tectonic activity at the boundary between … :10

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1) the African and the Indian-Australian Plates.

2) the Indian-Australian and Eurasian Plates.

3) the African and the Arabian Plates.

4) the Arabian and the Indian-Australian Plates.

5) the African and Antarctic Plates.

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Plate TectonicsTectonic plates move with respect to each other.

Where plates move toward each other, plates can be

pushed upward and downward → formation of mountain

ranges, some with volcanic activity, earthquakes

Where plates move away from each other, molten

lava can rise up from below → volcanic activity

Active Zones Resulting from Plate Tectonics

The interaction between the Pacific and the North American Plates is responsible for the formation of

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1) the Hawaiian Islands.

2) the Alps.

3) the Rocky Mountains.

4) the Andes.

5) the Appalachian Mountains.

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Volcanism on Earth (I)

Volcanism on Earth is commonly found along subduction zones (e.g., Rocky Mountains).

This type of volcanism is not found on Venus or Mars.

Subduction Zones

Example: Stromboli (Sicily, Italy, 1998)

Hawaii is also very volcanically active. Is this also because Hawaii is located at a plate boundary?

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1) Yes, it is located at the boundary of the Pacific plate.

2) Yes, it is located at the boundary of the North American plate.

3) Yes, it is located at the boundary of the Eurasian plate.

4) No. This must be a different kind of volcanic activity.

5) No. Hawaii is not volcanically active.

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Shield Volcanoes

Found above hot spots:

Fluid magma chamber, from

which lava erupts repeatedly through

surface layers above.

All volcanoes on Venus and Mars are shield volcanoes

Volcanism on Earth (II)

Shield Volcanoes (II)Tectonic plates moving over hot spots producing

shield volcanoes → Chains of volcanoes

Example: The Hawaiian Islands

Earth’s Tectonic History

Earth’s Tectonic History (II)

History of Geological Activity

Surface formations visible today have emerged only very recently compared to the age of Earth.

Guess: How thick is the Earth’s breathable atmosphere (beyond which you would need oxygen masks to breathe), compared to the Earth’s radius?

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1) 1/24,000 Earth radius.

2) 1/800 Earth radius.

3) 1/15 Earth radius.

4) 1 Earth radius.

5) 10 Earth radii.

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Earth’s Atmosphere

Only about 1/800 of the

Earth’s radius!

Which is the most common gas in Earth’s atmosphere?

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1) Oxygen

2) Nitrogen

3) Carbon dioxide

4) Methane

5) Water vapor

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The Atmosphere

Earth had a primeval

atmosphere from

remaining gasses

captured during

formation of Earth

Do you think that the Earth’s atmosphere is still very similar to what it was about 4 billion years ago?

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1) Yes

2) No

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The Atmosphere

Atmospheric composition severely altered (→ secondary atmosphere) through a combination of several processes:

Earth had a primeval

atmosphere from

remaining gasses

captured during

formation of Earth

Sources of Atmospheric Gas• Outgassing: Release of gasses bound in compounds in

the Earth’s interior through volcanic activity

• Later bombardment with icy meteoroids and comets

Loss of Atmospheric Gas• Chemical reactions in the oceans

• Energetic radiation from space (in particular, UV)

Which of these processes might be the main reason that Mercury has almost no atmosphere?

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1. Thermal Escape

2. Stripping by energetic radiation from space

3. Condensation

4. Chemical reactions

5. Ejection by impacts

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Which of these forms of radiation from space can reach the Earth unabsorbed?

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1) Radio waves.

2) Infrared light.

3) Ultraviolet light.

4) X-rays.

5) Gamma-rays.

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The Electromagnetic Spectrum

Need satellites to observe

Wavelength

Frequency

High flying air planes or satellites

The Interactions between Light and Molecules

X-rays

1) Splitting up molecules into atoms:

Nitrogen (N2) / Oxygen (O2)

2) Ionizing (kicking electrons out of) atoms or molecules

The Interactions between Light and Molecules

Ultraviolet

Splitting up molecules, in particular, Ozone:

Ozone (O3)Oxygen (O2)

Why is the totally eclipsed moon visible at all (in a faint red glow)?

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1) Because it is still glowing from the intense light it received during full moon before the eclipse.

2) Because it is illuminated by sunlight reflected off other terrestrial planets.

3) Because it is illuminated by sunlight scattered within the Earth’s atmosphere.

4) Because it is very shy during the eclipse and turns red when you are looking at it.

5) None of the above: The totally eclipsed moon is completely black.

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The Interactions between Light and Molecules

Penetrates through the atmosphere mostly unabsorbed,

but can get scattered:

Visible Light

This is why the sun appears red at

sunrise and sunset; and why the sky is

blue (if it’s not cloudy)

The Interactions between Light and Molecules

Carbon dioxide (CO2) /

Water vapor (H2O) /

any other asymmetric molecules (greenhouse

gases)

Infrared

Causes asymmetric molecules to rotate

This is the essential step of the

Greenhouse Effect!

We know that UV and X-ray radiation from space is heating the atmosphere. Thus, do you expect that the atmosphere becomes

hotter or colder with height, very high above the ground?

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1) Hotter with increasing height.

2) No temperature change.

3) Colder with increasing height.

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The Temperature Structure of Earth’s Atmosphere

Exosphere: Heated by UV and X-rays from space

Thermosphere: Heated by X-rays from space

Stratosphere: Heated by UV radiation from space

Troposphere: Heated by greenhouse effect

Ozone Layer

Atmosphere gets colder at larger distance from heat sources.

Top of Ozone Layer

Temperature

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