Unit A What Do You Know Now?

At the beginning of this unit you agreed or disagreed with statements about the composition of the Earth. Not all of the statements were true. Now that you have completed the unit, carefully think about each statement again then decide whether you agree or disagree with the statement based on what you have learned. How many of your responses changed?

  1. Oxygen is the main component of our atmosphere. (Agree / Disagree)

    Nitrogen is the main component of our atmosphere. See "A1 - Earth as a System" for more information.
  2. The crust, the part of the Earth that we stand on, has an average thickness of 100 km (approximately 62 miles). (Agree / Disagree)

    The Earth's crust has an average thickness of about 30 km (approximately 19 miles). See "A2 - Earth's Layered Structure / Earth's Layered Structure" for more information.
  3. The very center of the Earth is liquid. (Agree / Disagree)

    The very center of the Earth is solid; the outer core is liquid. See "A2 - Earth's Layered Structure / Earth's Layered Structure" for more information.
  4. The temperature just 80–100 km (approximately 50–62 miles) below the Earth's surface is estimated to range between 650–1,200° C (approximately 1,200–2,200° F). (Agree / Disagree)

    See "A2 - Earth's Layered Structure / Where Does the Heat Come From?" for more information.
  5. The interior of the Earth is heated primarily by radioactive decay. (Agree / Disagree)

    See "A2 - Earth's Layered Structure / Where Does the Heat Come From?" for more information.
  6. Continental crust is denser than oceanic crust. (Agree / Disagree)

    Continental crust has an average density of 2.7 g/cm3 while oceanic crust has an average density of 3.0 g/cm3. See "A3 - Oceans and Continents / Types of Crust" for more information.
  7. The most common element in the Earth's crust is iron. (Agree / Disagree)

    The most common element in the Earth's crust is oxygen. See "A3 - Oceans and Continents / Did You Know? - The Sign of the Four" for more information.
  8. There is a 70,000-kilometer-long (approximately 43,500-mile-long) range of mountains that follows a fairly continuous line through all the oceans of the world. (Agree / Disagree)

    See "A3 - Oceans and Continents / Deep Ocean Basins" for more information.