Iron Lung

Iron is crucial to your health. It helps carry oxygen through the body, so if you don’t have enough, you feel tired and sluggish. But too much iron isn’t good, either; in some cases, it can lead to diabetes or even heart failure.

The same thing applies to much of the microscopic life in the oceans: Iron is a key nutrient, but too much of a good thing can be bad. Overdoses of iron in single-celled organisms more than two billion years ago may have slowed the evolution of Earth’s atmosphere.

These organisms are known as cyanobacteria, and they’re still around today. As they convert nutrients and sunlight into usable energy, they release oxygen. Much of it bubbles to the surface and enters the atmosphere.

In fact, cyanobacteria were responsible for giving Earth an oxygen-rich atmosphere in the first place. The early atmosphere contained almost no oxygen at all. As cyanobacteria developed and spread, though, they pumped vast amounts of it into the air. There was an especially big uptick about 2.3 billion years ago.

A recent study, though, says that large amounts of iron in the water may have slowed things down. Iron-rich water was released from volcanoes on the ocean floor. The iron overloaded many of the microscopic organisms, killing them off. So the atmosphere got its oxygen in waves. When there was just the right amount of iron, lots of oxygen was added. But when there was too much iron, the process slowed down — delaying the transformation to the life-supporting blanket of air we enjoy today.