1. A100 Oct. 6 The Earth READ Chapter 5 – The Earth Homework 4 Due Friday
Quiz on Friday
Today’s APOD
The Sun Today

2. Looking outward to the blackness of space, sprinkled with the glory of a universe of lights, I saw majesty – but no welcome. Below was a welcoming planet. There, contained in the thin, moving, incredibly fragile shell of the biosphere is everything that is dear to you, all the human drama and comedy. That’s where life is; that’s where all the good stuff is.
Loren Acton (1936 – )
U.S. astronaut

3. The Earth from Space
Understanding Earth helps us understand other planets
Understanding other planets helps us understand the Earth
How has Earth has changed over time
Why does it change?
How does it differ from other planets?

4. Size and Shape of the Earth
The Earth is a huge, rocky sphere spinning in space and moving around the Sun at a speed of about 100 miles every few seconds
Earth also has a blanket of air and a magnetic field that protects the surface from the hazards of interplanetary space

5. Earth Data Distance from Sun Orbital velocity Orbital period
1 AU = 1.5 x 108 km
Orbital velocity
30 km / second
Orbital period
days
Rotation period
hours
Inclination of equator to orbit:
23.26 degrees
Diameter: 12,756 km
Mass 6 x 1024 kg
Mean density
5.5 gm/cm3
Surface temperature
-130 F to +140 F (avg. 70F)

6. An Average Planet Our Earth is about average
Earth is the largest and most massive of the four terrestrial planets, but smaller and less massive than the four giant, or Jovian, planets.
Earth is third in distance from the Sun among the four terrestrial planets.
Earth has a moderately dense atmosphere; 90 times less dense than that of Venus but 100 times denser than that of Mars.

7. Unique Features of Earth
Plate Tectonics – the only planet with a surface shaped by this type of tectonics
Atmospheric Oxygen – the only planet with significant Oxygen in its atmosphere
Surface Liquid Water – the only planet where temperature & pressure allow surface water to be stable as a liquid
Climate Stability - differs from Venus & Mars in having a relatively stable climate
Life – The only world known to have life; it certainly has abundant & diverse life forms
Magnetic Field
Large moon

8. Size and Shape of the Earth
The Earth is large enough for gravity to have shaped it into a sphere
More precisely, Earth’s spin makes its equator bulge into a shape referred to as an oblate spheroid – a result of inertia

9. Composition of the Earth
The most common elements of the Earth’s surface rocks are:
oxygen (45.5% by mass),
silicon (27.2%),
aluminum (8.3%),
iron (6.2%),
calcium (4.66%), and
magnesium (2.76%)
Silicon and oxygen usually occur together as silicates
Ordinary sand is the silicate mineral quartz and is nearly pure silicon dioxide

10. Density of the Earth
Density is a measure of how much material (mass) is packed into a given volume
Typical unit of density is grams per cubic centimeter
Water has a density of 1 g/cm3, ordinary surface rocks are 3 g/cm3, while iron is 8 g/cm3
For a spherical object of mass M and radius R, its average density is given by
For Earth, this density is found to be 5.5 g/cm3
Consequently, the Earth’s interior (core) probably is iron (which is abundant in nature and high in density)

11. What’s Inside?
Crust
Asthenosphere
Mantle
Outer Core
Inner Core

12. How do we know this? A sonogram of the Earth
Earthquakes generate seismic waves that move through the Earth with speeds depending on the properties of the material through which they travel
These speeds are determined by timing the arrival of the waves at remote points on the Earth’s surface
A seismic “picture” is then generated of the Earth’s interior along the path of the wave

13. Interior Structure of the Earth
A solid, low-density and thin crust made mainly of silicates
A hot, thick, not-quite-liquid mantle with silicates
A liquid, outer core with a mixture of iron, nickel and perhaps sulfur
A solid, inner core of iron and nickel

14. Differentiation
The densest materials are at the center of the Earth and the least dense materials are at the surface – differentiation
Differentiation occurs in a mixture of heavy and light materials if these materials are liquid for a long enough time
The Earth must have been almost entirely liquid in the past

15. Earth’s Interior
Earth’s interior gets hotter towards the center (6500K, as hot as the Sun’s surface)
The Earth’s inner nickel/iron core is solid because the high pressure (from overlying materials) forces it into a solid state – even at that high temperature
The outer core is liquid nickel/iron

16. Why so hot???
The high temperature in the Earth’s core (6500K) is probably due to two causes
Left-over heat from the impact of small bodies that eventually formed the Earth
The radioactive decay of radioactive elements that occur naturally in the mix of materials that made up the Earth

17. The Earth cools very slowly
Pseudo-color infrared image of the Earth from space. The red areas are warm water during an El Nino event
Heat is trapped inside the Earth’s interior due to the long time it takes to move to the surface and escape

18. Age of the Earth Radioactive decay used to determine the Earth’s age
Radioactive atoms decay into daughter atoms
The more daughter atoms there are relative to the original radioactive atoms, the older the rock is

19. Age of the Earth
Radioactive potassium has a half-life of 1.28 billion years and decays into argon, which is a gas that is trapped in the rock unless it melts
Assume rock has no argon when originally formed
Measuring the ratio of argon atoms to potassium atoms gives the age of the rock
This method gives a minimum age of the Earth as 4 billion years
Other considerations put the age at 4.5 billion years

20. Early History of Earth Four main stages of evolution: Differentiation
Early History of Earth
Four main stages of evolution:
Differentiation
Bombardment
Cooling
Surface evolution
Earth formed 4.6 billion years ago from the inner solar nebula
Most traces of ancient bombardment (impact craters) have been destroyed by later geological activity

21. Meteorite Impacts Still Occur
Meteorite Impacts Still Occur
Famous example: Barringer Crater near Flagstaff, AZ:
1.2 km diameter
200 m deep
Over 150 impact craters found on Earth.
Formed ~ 50,000 years ago by a meteorite of ~ 80 – 100 m diameter

22. The Chicxulub Crater
Comet nucleus impact producing the Chicxulub crater ~ 65 million years ago may have caused major climate change, leading to the extinction of many species, including dinosaurs.
The impact of a large body formed a crater ~ 180 – 300 km in diameter in the Yucatán peninsula, ~ 65 million years ago
Evidence of the event is seen in rock layers around the world

23. Dates to Remember ASSIGNMENTS this week READ Chapter 5 – The Earth
Homework 4 Due Friday
Quiz on Friday