popular science

faint young sun paradox

Let me take you to a 4.54 billion years deep dive into the past.
Earth just started to form, in approximately one-third the age of the universe, by accretion from the solar nebula. It is a love at first space sight.
And now a big IF.
If you are to look up at the sky 4 billion years ago, you would have seen a sun way dimmer than the one you see and feel on your skin today.
And down on young Earth, you’d see just an expanse of bobbing waves. This is important.
Bear with me.
Because, that’s the problem – a simple one, but, oh, a big one. Scientists have been twisting their brains with it for more than five decades.
The evidences for these two facts about our early planet house – a dim sun and liquid oceans – were strong even in the ‘60s.
Astronomers have compared our sun today to other stars of different sizes and ages, and they’ve been able to reconstruct much of its history.
The sun started out about (only) 70% as bright and warm as it is in 2018.
But then, an astro step by step, our star slowly grew brighter.
Even 2 billion years ago (and 2.5 billion years *after* the Earth has formed), the sun was still just 85% as bright as today.
On its own, the faint young sun could not have kept the Earth from freezing over out there in the space.
Wait, what? How are we even alive today, then?
We’re still figuring out.
There’re a lots of signs in ancient rocks that the Earth was wet. Tiny crystals, old af, aka 4 billion years, have a chemistry that required liquid water. Ancient rocks known as pillow lavas must have formed as molten Earth oozed out into sea water.
During the mid-60s, scientists put a finger on their foreheads and realised — these two evidences pose a certain paradox.
Faint Young Sun Paradox.
It was a damn big problem that required some serious thought. It didn’t just mean that the evidence from geology and astronomy wasn’t meshing together. It also added a puzzle to the rise of life on Earth. Life would have had a hard time getting started on a planet of ice.
In 1972, dear Carl Sagan and his colleague at Cornell, George Mullen, proposed a solution to the paradox: the Greenhouse effect.
When radiation from the sun hits the Earth, some of it bounces back into space and some of it just hangs out it the space, thanks to heat-trapping gases in the atmosphere.
In the neighborhood, the early Earth would have released gasses from its rocks, creating the first atmosphere.
If it had the right chemistry, it might have been able to keep the Earth warm enough to melt ice.
They suggested ammonia as a plausible heat-trapper on the young planet.
Unfortunately, ammonia turned out to be a bad solution.
Other scientists figured out that ultraviolet rays from the sun would have destroyed any built up ammonia in the atmosphere in less than a decade. That’s not much of a defense against the deep freeze.
But ammonia is not the only greenhouse gas in the game.
Today, carbon dioxide and methane are two important molecules keeping our planet warm (and warmer, and warmer, and warrrmer).
Scientists have tried for years to narrow down the possible range of the two gases on the early Earth. It’s a very tricky puzzle, because scientists know that there are many factors that can influence their concentrations.
So, scientists are looking at other possible factors.
Clouds may have helped.
The early Earth rotated quickly through a 14 hour day, which may have changed how the oceans circulated–and thus how they trapped heat.
But wide scope still remains for more ideas.
If hydrogen and nitrogen do turn out to be part of the answer to the Faint Young Sun Paradox, they may have some fascinating implications about life on Earth–and well…  elsewhere, cosmos wise!


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No more light wear, kiddos. It is cold, and ever-changing. Just yesterday, it was wet and freezing. Today: hello cold sun dearest! I have another paradox for you. It is called Faint Young Sun paradox. – Solution to It may give us an insight into how the hell are we even alive today when we know for a fact that 4 billion years ago, the sun was way dimmer and less hot than it is today. Translation: in theory, life on Earth would have a serious problem forming with ice and little energy comming from our star. Let’s talk about it. Just like Carl Sagan and George Mullen did in 1972. . . . . #popularscience #popscience #funfacts #sciencefactoftheday #faintyoungsunparadox #neuronenvogue #sciencefacts

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