Atmosphere

What was the Earth's atmosphere mostly made of 4.5 billion years ago?

• Nitrogen and carbon dioxide

• Methane and ammonia

• Oxygen and nitrogen

• Hydrogen and helium

Which organism was responsible for the first production of oxygen?

• Fish

• Green plants

• Cyanobacteria

• Fungi

What important role does the ozone layer play?

• It provides oxygen for breathing

• It keeps the Earth warm

• It helps plants grow

• It blocks harmful UV rays from the sun

What major change did humans bring to the atmosphere in the last century?

• Increased oxygen levels

• Decreased nitrogen levels

• Decreased water vapor levels

• Increased carbon dioxide levels

What is one effect of burning fossil fuels?

• Decreased oxygen levels

• Increased nitrogen levels

• Decreased methane levels

• Increased carbon dioxide levels