Question

the eruption of mount st. helens on may 18, 1980
volcanoes cycle carbon from below the earths surface back into the atmosphere. volcanoes emit co₂, ash, and other gases. over billions of years, volcanoes have added a significant amount of co₂ to the atmosphere.
however, the amount of co₂ that volcanoes contribute each year is small compared to other carbon sources. for example, the eruption of mount st. helens in washington emitted 10 million tons of co₂ into the atmosphere over 9 hours. by comparison, human activities release the same amount of co₂ in about 2.5 hours.
how do volcanoes affect the carbon cycle? select the true statements.

• more co₂ is emitted per year by volcanoes than by human activities.
• volcanic eruptions move carbon from the atmosphere to below earths surface.
• over billions of years, volcanoes have added co₂ to the atmosphere.
• volcanic activity is a carbon source.

Explanation:

• The text states "Over billions of years, volcanoes have added a significant amount of \(CO_2\) to the atmosphere", which supports the statement "Over billions of years, volcanoes have added \(CO_2\) to the atmosphere".
• Since volcanoes emit \(CO_2\) (as mentioned in the text), volcanic activity is a carbon source.
• The text says "the amount of \(CO_2\) that volcanoes contribute each year is small compared to other carbon sources", so "More \(CO_2\) is emitted per year by volcanoes than by human activities" is false.
• Volcanoes cycle carbon from below the Earth's surface back into the atmosphere (as per the first sentence of the text), so "Volcanic eruptions move carbon from the atmosphere to below Earth's surface" is false.

Answer:

• Over billions of years, volcanoes have added \(CO_2\) to the atmosphere.
• Volcanic activity is a carbon source.