Jun 25, 2026 · 2 min · 3 segments
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…
Scott TinkerHost
The atmosphere of early Earth was made up of methane, CO2, and sulfur gases, but no oxygen.
Eventually, as noted on a prior Earth date, 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.
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.
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.
The atmosphere of early Earth was made up of methane, CO2, and sulfur gases, but no oxygen.
Eventually, as noted on a prior Earth date, 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.
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.
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.
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