Earth's Structure and Life History

Approximately how long ago did Earth form?

• 1.5 billion years ago

• 2.4 billion years ago

• 3.8 billion years ago

• 4.5 billion years ago

Which of the following is the outermost layer of Earth's internal structure?

• Solid inner core

• Liquid outer core

• Silicate mantle

• Rocky crust

What is Earth's average distance from the Sun?

• 50 million miles

• 93 million miles

• 150 million miles

• 200 million miles

Why is Earth able to maintain water in all its forms (liquid, ice, and gas)?

• Its large size compared to other planets.

• Its unique distance from the Sun.

• The presence of a strong magnetic field.

• Its rapid rotation speed.

What makes Earth unique compared to other known places in the universe regarding water?

• It has the largest oceans.

• It is the only known place with liquid water on its surface.

• It has the most diverse forms of ice.

• Its water is constantly evaporating into space.

What were the earliest known life forms on Earth, appearing approximately 3.8 billion years ago?

• Photosynthetic bacteria

• Complex cells

• Microbial organisms

• First vertebrates

Approximately how long ago did plants emerge on Earth?

• 2 billion years ago

• 650 million years ago

• 500 million years ago

• 465 million years ago

How many species of plants, animals, bacteria, and fungi have been cataloged on Earth?

• Approximately 500,000

• Over 1 million

• Exactly 1.5 million

• An estimated 1.5 million