Privileged Planet: length of day helps life survive (Introduction)

by David Turell , Wednesday, November 03, 2021, 22:20 (904 days ago) @ David Turell

On early Earth days were much shorter and lengthened to help life develop:

https://www.nationalgeographic.com/science/article/how-earths-tides-may-be-linked-to-th...

"Judith Klatt had been studying microbes called cyanobacteria for years, and she was initially skeptical when some colleagues came to her with an idea: Could the length of a day on early Earth have mattered to the rise of life as we know it?

"Day length has increased dramatically over Earth’s history. More than three billion years ago, entire days may have been just six hours long. And around 2.4 to 2.2 billion years ago, geological records indicate that the amount of oxygen in the atmosphere shot up while the volume of carbon dioxide shrank. That rapid increase in oxygen is generally credited to the proliferation of marine cyanobacteria, some of which absorb energy from sunlight and produce oxygen.

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"Klatt, a microbiologist at the Max Planck Institute for Marine Microbiology in Germany, and her collaborators at the University of Michigan set out to investigate whether longer days could have let ancient cyanobacteria thrive, setting the stage for an explosion of early animals and, ultimately, the life-forms that exist today.

"To investigate that pattern, the team turned to a unique ecosystem on the bottom of Lake Huron called Middle Island Sinkhole. They paired oxygen concentration measurements in the cyanobacteria-rich sinkhole and experiments in the lab with computer models of Earth’s rotation.

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“'What they’ve shown is that biology cares whether the day-night cycle is 24 hours or 12 hours,” says Christopher Spalding, a planetary scientist at Princeton who was not involved in the research. “So I think that first-order finding is worth looking more at.”

"Our current roughly 24-hour day is the result of Earth’s spin slowing down over its 4.5 billion years, and much of that change can be linked to the tides.

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"The water in the 75-foot-deep sinkhole has high concentrations of sulfur and not much oxygen. Scientists think those conditions could be similar to the ancient ocean billions of years ago. By studying that environment, Klatt’s team can get an approximate idea for how similar ancient ecosystems could have behaved.

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"While short days have cyanobacteria constantly switching on and off, longer days let them photosynthesize for longer stretches of time, building up oxygen concentrations around them until some is driven out and up into the atmosphere. Indeed, Klatt’s laboratory experiments showed that when samples of the lakebed microbes were exposed to longer periods of daylight, they contributed more oxygen to the atmosphere.

"The spin-rate model Klatt used predicts that days lengthened steadily between 3.5 and 2.25 billion years ago. Once Earth, the moon, and the tides reached the resonance state at 21-hour days, they stabilized there until around 550 million years ago, when Earth’s spin began to slow down again. Settling into that long, stable day length would have been key for letting cyanobacteria hit their stride, optimizing their biological processes for a 21-hour day rather than continually adjusting to changing day length."

Comment: Yet another way the Earth evolved to be a perfect planet for life. Perhaps as God guided it.