purpose. Early earth had a mantle that wasn't very oxidized but was just waiting for oxygen to react with it. The gases emitted from early volcanoes reacted with oxygen as they were emitted. Hydrogen gas may have been one of these, reacting with oxygen to make water. It was only when the gases were mostly mixed with oxygen from bacteria that real oxygen gas could accumulate. As the mantle itself became oxidized, fewer of these gases were emitted and more gases that were already oxidized were more likely to be emitted from newer volcanoes. It's hard to know much about early volcanoes as the oldest volcano on earth – Mount Etna – is only about 350,000 years old.
VOLCANO ANATOMY What are the pieces and parts of a volcano? They all look different but have similar parts to their anatomy. This brief glossary covers things you'll see in figure 31 on volcano anatomy:
Figure 31.
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