Earth's Surface Systems Are Ultimately Powered by the __________

Q29: Oceans cover _ percent of the Earth's

Q30: The central portion of the Earth, called

Q31: Earth's core consists mostly of _.<br>A) iron

Q32: Imagine that a system has been perturbed

Q33: The Earth's population (in mid-2009) was about

Q35: Gradualism states that:<br>A) the Earth is uniform

Q36: A _ _ occurs when a small

Q37: The _ is a mixture of gases,

Q38: The core is:<br>A) the least dense layer

Q39: Earth's crust is part of the:<br>A) hydrosphere.<br>B)