You probably already know a lot about the composition of the Earth from your own general knowledge. You may have picked up this background from your own reading, from TV, from movies, or from other areas. Below you will find a series of statements concerning Earth's composition. Not all of them of them are true. All of the concepts in the statements will be fully explored in the lessons, but before you review the lessons, let's see what you already know about the composition of the Earth. Carefully think about each statement. Then decide, to the best of your knowledge, whether you agree or disagree with each statement. At the end of the unit, you'll be able to review these statements again to see how much you have learned.

1. Oxygen is the main component of our atmosphere. (Agree / Disagree)
   
   
2. The crust, the part of the Earth that we stand on, has an average thickness of 100 km (approximately 62 miles). (Agree / Disagree)
   
   
3. The very center of the Earth is liquid. (Agree / Disagree)
   
   
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)
   
   
5. The interior of the Earth is heated primarily by radioactive decay. (Agree / Disagree)
   
   
6. Continental crust is denser than oceanic crust. (Agree / Disagree)
   
   
7. The most common element in the Earth's crust is iron. (Agree / Disagree)
   
   
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)