And it’s the rock record that gives us the major clue about how we got to be such a lively, oxygen-rich planet. Abrupt and striking changes in the rock layers indicate that oxygen levels shot up without warning – this happened repeatedly, over billions of years. This pattern would certainly fit with the behaviour of volcano eruptions, but how could these dirty and destructive events have given us clean air?
When a volcano erupts, it injects ash and volatile gases into the atmosphere, and this impacts on the surrounding landscape and on carbon-levels in the air. But very early in Earth’s history, when there was much less oxygen in our atmosphere, the injection of these volatile gases into the air would have had a much greater effect. Oliver explains: “With little else to dilute the mix, these gases would have hugely altered the surrounding atmosphere. They would have set off all sorts of chain reactions in the environment, and it’s likely that these reactions eventually led to the introduction of O2 into our atmosphere.”
But to further investigate this theory, Oliver needed to get his hands on a sample from the front line. Volcanoes emerge because the Earth’s plates are constantly moving. When two plates meet, one plate is dragged underneath the other. As bits of the Earth’s crust are pulled down into the mantle, they leave a tear in the Earth’s surface, and it’s from this tear that volcanoes emerge. The mid-Atlantic ridge is an underwater stretch of volcanoes that have sprung up along the tear between two plates, all the way from the Antarctic to the Arctic. At one point, the volcanoes actually peep above the surface of the water, forming the inaptly-named country of Iceland.