Transcript Part7Unit2EarthAgeandOriginUniqueness

Unit 2
The Earth in Space
Origin of the Earth
Earth’s Age

Meteorites are the Key
• Chrondite meteorites contain small round
granules called silicate minerals
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These granules contain water and other volatile
elements that turn into gases at low temperatures
Significance:
• These meteorites have not melted since their
formation

Remember: Water evaporates
• Radioactive decay ages meteorites at 4.6
billion years
Origin of Earth

Series of Events
• Ignition of the Sun’s core
• Accretion
• Melting of the Earth Interior
• Differentiation
• Forming the atmosphere
• Finally, an atmosphere with significant
amounts of Oxygen
Earth’s Growth

Accretion
• After the solar wind (T. Tauri wind) cleared
out much of the solar system
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Meteorites and planetismals collided with Earth;
Earth got bigger; gravity increased; more
meteorites pulled in
Meteorite materials: Oxides of silicon, iron,
magnesium, and metallic iron with small
amounts of radioactive decay
Meteorite impact created heat which
kept the surface molten
• Time frame: Few million years
Forming the Core

Interior of Earth melted as a result of:
• Meteorite impacts
• Gravitational pressure
• Radioactive decay

Differentiation
• The process by which compounds of different
densities separated into distinct layers within the
molten interior of the earth to form the core,
mantle and crust
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Heavy elements like iron and nickel sunk to the center to
form the core
Lighter elements like silicon, magnesium and aluminum
rose to the surface forming the mantle and the crust
Forming the Atmosphere

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When the interior of Earth melted,
gases such as carbon dioxide, sulfur
dioxide, hydrogen, ammonia,
methane, and water vapor were
released and moved towards the
surface
Earth’s surface was becoming solid
as temperatures cooled (freezing to
boiling point)
Forming Life

As temperatures cooled, water vapor in the
atmosphere converted to liquid
• Now the oceans formed

Life
• 3.5 to 3.8 billion years ago
• Species appeared that used photosynthesis
producing free oxygen as a by-product

Free oxygen: oxygen that is not bound with any other
element
• This free oxygen continued to increase in
amount and eventually resulted as a counterpart
of the atmosphere we have today.
Uniqueness of Planet Earth


Only planet where water exists in three
states
Continuously habitable zone
• Theoretically, this is a zone in the solar
system where a planet’s surface
temperature ranges from -80oC and 100oC
over a long enough period for life to evolve.

Mars also exists in this zone
• Problem: Mars can’t hold its atmosphere
Assignment #1

Handout Assignment #1
• Use Chapter 2 and notes to answer the
questions.
• Answers to follow.
Assignment #1
Q1. Why is it difficult to learn much about earth’s
history by examining surface rocks?
A. Surface rocks are the result of the lighter elements
moving to the surface during the process of
differentiation and then the molten surface cooling.
Q2. How have meteorites helped tell us about the
early history of the Earth?
A. Chondrite meteorites help us age the Earth. These
meteorites contain small, round granules of silicate
material that contain water and other volatile
elements that didn’t turn to gas (the meteorites
didn’t melt so gas wasn’t formed). Since these
materials are still present, nothing has happened to
the meteorite since its formation. Radiometric
dating has aged these to 4.6 billion years.
Assignment #1
Q3. Explain the processes of accretion and
differentiation.
A. Accretion deals with the formation of the planets
through the accumulation of materials.
Differentiation deals with the outward movement of
lighter elements to the surface forming the mantle
and the crust. The heavier elements sink to the
center of the Earth forming the core.
Q4. In your opinion, what was the single most
important event in Earth’s history?
A. Possible answers.
•
Big Bang Theory
•
Cooling of the surface to solidify
•
Formation of the atmosphere
•
The release of oxygen as a by-product.
Assignment #1
Q5. Why is the study of astronomy topics
included as part of a study of the Earth?
A. Possible answer. Knowing how the Earth
was possibly formed gives insight into how to
study it, explains why things are happening,
and gives insight into where Earth is headed.
Q6. In what ways is the Earth unique?
A. The Earth is located in the Continuously
Habitable Zone (CHZ)