Chapter 4 study guide
(this is a guide for studying…remember 5 times is the magic number for reading the textbook and studying the mayo
notes will help you as well) 
Section 1
1. How long ago do scientists believe the solar system was formed?
i. 4.6 billion years ago
b. What was it formed from?
i. A very large cloud of gas and dust
c. How much of the material became the sun?
i. 90%
d. Everything else?
i. 10%
2. In 4 steps, describe the nebular hypothesis
a. A large cloud of interstellar gas and dust begins to condense
b. The cloud’s material converges, spinning faster and growing hotter. A cooler cloud of ice and rock is
surrounded by hotter gas
c. As fusion first occurs in the new star, planetessimals form and begin to attract more and more material
as they orbit
d. Over time nearly all the material from the original cloud becomes part of the star and its orbiting planets
3. What is an oblate spheroid?
a. A sphere that is slightly flattened at the poles and bulges in the center
4. How did scientists determine the Earth is an oblate spheroid?
a. The weight of a specific object at several different locations around the globe (allowing for altitude)
5. Would you weigh more or less on the top of Mount Everest (compared to sea level)?
i. Less
b. Why?
i. Because you are farther away from the center of gravitational force.
6. According to scientists, the primordial Earth looked a lot like the moon, what happened to allow it to change
into the dynamic, multi-layered planet it is today?
a. In its early history, Earth was constantly bombarded by material left from the formation of the solar
system, these impacts provided the heat for the melting of the material to be divided according to
density
7. What are the six layers of the Earth?
a. (from the inside out) Inner core, outer core, mantle (which is divided into the lower mantle,
asthenosphere, and lower lithosphere) and the crust
8. What are three things that give rise to Earth generated heat?
a. Meteorite impacts
b. Friction from overlying rock layers
c. Radioactive decay of unstable isotopes
9. Earth has been losing heat since its formation, why does heat loss vary place to place?
a. Rocks lose heat differently
b. Thickness of Earth’s crust varies from place to place
c. The percentage of radioactive materials varies from place to place
10. As depth below Earth’s surface increases, what happens to temperature and pressure?
a. It increases in both pressure and temperature
11. In the 1900s scientists developed a theory on how Earth’s magnetic field was generated, explain this hypothesis
a. The solid inner core of iron and nickel spins inside the liquid outer core of iron in nickel creating a very
strong magnetic field
Section 2
1. How long does one rotation of Earth take?
a. Approximately 24 hours
2. An imaginary line goes through the earth from the North Pole to the South Pole, what is this line called?
a. Axis
3. What are the two primary pieces of evidence that prove the Earth rotates?
i. Foucault pendulum
ii. Coriolis effect
b. Explain both of these pieces of evidence
i. Foucault pendulum: Once a pendulum is put in motion swinging in a certain direction, it will
remain moving in that direction. However because the earth spins below the pendulum, it
appears to change direction by approximately 11 degrees/hour. After 8 hours it appears to be
swinging 90 degrees (or perpendicular) from the direction it started.
ii. Coriolis effect: Winds on earth will always blow from high pressure (inside the balloon, from the
demo) to areas of low pressure (outside the balloon from the demo) in a straight line. However
winds are deflected to their right in the northern hemisphere and left in the southern
hemisphere because the earth spins underneath them causing them to curve.
4. What is an orbital plane?
a. The imaginary line on which an object will revolve around another object in space
5. At what angle does Earth’s axis intersect with its orbital plane?
i. 23.5 degrees (from perpendicular to its orbital plane)
b. Why is this so important?
i. It is the tilted axis which creates the change in length of days and angle of incoming solar
radiation that creates our seasonal change in temperatures.
6. Explain why the Earth spins faster at the Equator than the poles.
a. The earth rotates approximately 15 degrees/hr. because 15 degrees of longitude is a shorter distance at
the poles than the equator, the distance traveled per hour will be less, which means that area will spin
more slowly.
7. From the standpoint of the North Pole, which way does Earth rotate?
a. Counterclockwise
8. What happens because the Earth rotates 1 time every 24 hours?
a. We experience the change from night to day as the Earth spins towards the sun and then away from the
sun
9. What is the difference between clock time and solar time?
a. Clock time is the average solar time within a time zone, while solar time is time as measured by the
movement of the sun. Solar noon is when the sun is at its highest position in the sky while clock noon
occurs when one averages the movement of the sun across a given time zone
10. How many standard time zones are there?
a. 24
11. How many degrees of longitude is each standard time zone?
a. Each standard time zone is approximately 15 degrees
12. Any line of longitude exactly divisible by 15 is called…?
a. A time meridian
13. What is the prime meridian?
a. An arbitrary longitude line that passes through Greenwich England that is the beginning of the longitude
lines, or 0 degrees
14. Why is every time zone NOT exactly 15 degrees wide?
a. Because time zones cannot cross towns, or cities. It also tries to allow for small countries to all have the
same clock time.
15. What is the International Date Line?
i. It is found at 180 degrees of longitude, it is on the opposite side of the world from the Prime
Meridian
b. How is it different from the other lines of longitude?
i. When you cross this line to the East, it is one day earlier. When you cross it to the west, it is one
day later.
Section 3
1. What is revolution?
a. The movement of one object in space moving around another object
2. Explain the piece of evidence for revolution and what it this evidence is called
a. Parallax: Parallax is the apparent shift of nearby stars in relation to far away stars as the Earth moves
through it’s orbit.
3. In which direction is Earth revolving as seen from the North Pole?
a. Counterclockwise
4. Explain how seasons are NOT related to distance from the sun
a. We are closest to the sun on January 2nd which is the Northern hemisphere’s coldest time of year
5. When the Earth is closest to the sun, what is this called?
a. Perihelion
6. When the Earth is farthest from the sun, what is this called?
a. Aphelion
7. How long does it take for the Earth to make one complete revolution around the sun?
a. 365.25
8. At what rate does the Earth revolve around the sun?
a. About 1 degree per day
9. What does it mean when the sun is at Zenith?
a. It means the sun is at its highest altitude (90 degrees) in the sky for the day
10. Is the sun at Zenith (at some point in the year) at every location on Earth?
i. No
b. Explain this answer
i. Any latitude north of 23.5 degrees (north of the Tropic of Cancer) will never have the sun at
Zenith
ii. Any latitude South on 23.5 degrees (south of the tropic of Capricorn) will never have a sun at
zenith
11. What two things are responsible for seasons on Earth?
a. Revolution around the sun and axial tilt
12. The tilt of the Axis of Earth does two things that affect temperatures on Earth, what are they?
a. It will create a change in the length of day (summer days are longer than winter days)
b. It will create a change in the altitude of the sun (the sun will reach a higher altitude in the sky during the
summer than the winter)
13. Explain where the overhead sun is located, the date, and the name of the following times of year
a. First day if summer (northern hemisphere) 23.5 degrees north of the Equator (Tropic of Cancer)
b. First day of fall (northern hemisphere) 0 degrees (Equator)
c. First day of winter (northern hemisphere) 23.5 degrees south of the Equator (Tropic of Capricorn)
d. Frist day of spring (northern hemisphere) 0 degrees (Equator)
14. How is it possible for there to be 24 hours of daylight or darkness for months in a row at the poles?
a. On December 21, it is the winter solstice, which marks the first day of winter in the northern
hemisphere. The sun will be at its lowest altitude and shortest arc across the sky. On this day the axis of
the Earth is pointed its maximum tilt away from the sun