| A molecule of ____ contains three oxygen atoms. |
contour |
| The Earth's atmosphere is mostly ____ and oxygen (O2) gasses. |
core |
| The Earth's ____ is composed of hot iron and nickel. |
ebb |
| About 66 million years ago, a massive ____ hit the Earth. |
mantle |
| The tide stages are flood tide, high tide, ____ tide, and low tide. |
meteorite |
| The scientific study of earthquakes is called ____. |
nitrogen |
| The Earth's ____ is mostly solid rock between its crust and core. |
ozone |
| A ____ line (isoline) joins points of equal elevation (height). |
seismology |
