One of my favorite activities is roasting s’mores over the campfire in the cool of the evening. Everyone knows you need graham crackers, chocolate squares, and marshmallows to make s’mores. But one essential “ingredient” that often goes unnoticed is the atmosphere’s oxygen content. For the last 50 million years, this important gas comprised 20 percent of the atmosphere. New research indicates that this value fluctuated dramatically in earlier times.
Attempts to measure Earth’s past oxygen content often give conflicting results. This difficulty arises because scientists cannot directly measure the ancient atmospheric gases but must use proxies instead. Numerous variables affect the geological record, oxygen being just one of those variables. However, a team of scientists recently found a way to control for all the other variables by using coal as a proxy for past oxygen content.
Without oxygen, nothing burns—but with enough oxygen, even wet objects readily combust. Thus, the researchers were able to use charcoal (burned organic matter) formed in water-rich environments as the proxy. The amount of charcoal in coal depends primarily on the amount of gaseous oxygen available and coal’s economic value means a large database of charcoal compositions already exists. The information in this database demonstrates that even with dramatic climate changes over the last few million years the amount of coal remained relatively uniform. This matches the expectation that the oxygen content of the atmosphere remained constant over the past 50 million years.
However, over the last 400 million years, the oxygen showed dramatic increases and decreases compared to current values.1 Past life on Earth may have been well adapted to these changes, but similar changes today would cause significant problems for humanity. Too much oxygen in the atmosphere leads to explosive and destructive wildfires. Too little oxygen means less energy is available to fuel biochemical reactions inside large-bodied organisms, like humans.
An increasing body of evidence shows that Earth’s environment changed numerous times in ways that altered the kinds of life able to survive on the planet. Yet humanity arrived on the scene during a stable period when the atmospheric oxygen met all the criteria that advanced life requires. Such fine-timing follows if a supernatural Designer is preparing a place for human life.