Section 20.3 and 20.4

What bodies in the solar system collided and combined to form Earth?

• planetesimals
• stars
• globules
• craters

What factors caused the shape and structure of Earth?

• gravity and energy
• heat and pressure 
• gravity and heat
• energy and pressure

Earth's layers formed as rocks melted and 

• heavier and lighter elements separated
• lava from volcanoes covered Earth
• different landforms developed
• earthquakes caused elements to settle

The layer of Earth that extends to the planet's center is the

• crust 
• corona
• mantle 
• core

The middle layer of Earth is the 

• crust
• meridian
• mantle
• core

The layer of Earth that has the lightest elements is the 

• mantle 
• core
• crust
• ozone

Early life-forms released oxygen into Earth's atmosphere through the process of 

• photosynthesis
• osmosis
• oxidation
• pollination

Scientists think that Earth's first atmosphere was made up of

• oxygen and water vapor
• carbon dioxide and water vapor
• volcanic gases and dust
• hydrogen and cirrus clouds

Scientists think oceans may have formed after millions of years of 

• evaporation
• rainfall
• flooding
• humidity

One complete trip along an orbit

• rotation 
• orbit
• revolution
• period of revolution