Billions of years ago, the globe spun twice as fast as today; a complete rotation took just 6 hours.

Then Earth’s rotation slowed, and that’s why you’re here listening to this episode. Let me explain.

The atmosphere of early Earth was made up of methane, CO2 and sulfur gases. But no oxygen.

Eventually, as noted on a prior EarthDate, cyanobacteria, blue-green algae, began to produce oxygen through photosynthesis.

At first, the amount of oxygen they released was so small that it was absorbed by iron in seawater, and no oxygen entered the atmosphere.

Scientists researching this phenomenon found a similar low-oxygen, high-sulfur environment in sinkholes at the bottom of Lake Michigan, where modern blue-green algae grows.

There, and in a lab mimicking that environment, they tested the effects of day duration on oxygen production.

Turns out blue-green algae is dormant in the morning. In a short day, it was nearly dark again by the time it started producing oxygen.

And that small amount was reabsorbed by the algae before it could enter the water.

As days lengthened, the algae had enough time to produce enough oxygen to escape.

Over millions of years, oxygenated water first gave rise to aerobic sea life.

Then an oxygen-rich atmosphere allowed land creatures to develop and thrive, which eventually led to…

you, and me, and a radio show called EarthDate.