Question

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. over billions of years, volcanoes have added co₂ to the atmosphere. volcanic eruptions move carbon from the atmosphere to below earths surface. volcanic activity is a carbon source.

Explanation:

1. Analyze the first statement: The text says human activities release the same amount of \( \text{CO}_2 \) as Mount St. Helens' eruption (10 million tons) in ~2.5 hours, while volcanoes' annual emission is small compared to human activities. So "More \( \text{CO}_2 \) is emitted per year by volcanoes than by human activities" is false.
2. Analyze the second statement: The text states "Over billions of years, volcanoes have added a significant amount of \( \text{CO}_2 \) to the atmosphere", so this is true.
3. Analyze the third statement: The text says volcanoes cycle carbon from below the Earth’s surface back into the atmosphere, not the other way. So "Volcanic eruptions move carbon from the atmosphere to below Earth’s surface" is false.
4. Analyze the fourth statement: Volcanoes emit \( \text{CO}_2 \), ash, and other gases, so they are a carbon source (adding carbon to the atmosphere). This is true.

Answer:

• Over billions of years, volcanoes have added \( \text{CO}_2 \) to the atmosphere.
• Volcanic activity is a carbon source.