What color was the sky millions or billions of years ago?
August 22, 2011 7:16 PM   Subscribe

What color was the sky millions or billions of years ago?

The composition of the atmosphere has varied wildly over the last six billion years, with the levels of oxygen, nitrogen, and CO2 fluctuating throughout. So wouldn't the apparent color of the sky—to a human's perception—have changed along with it? If so, what is the range of colors that it's appeared?
posted by waldo to Science & Nature (7 answers total) 21 users marked this as a favorite
According to meteorologist Tom Skilling, it was actually much the same, at least back in dinosaur times.
Dinosaurs lived from 245 million to 65 million years ago, and the same kinds of cumulus clouds that you observe in our present-day summer sky assuredly populated the dinosaurs’ sky as well. The laws of atmospheric physics are immutable. Even assuming the gaseous composition of the Earth's atmosphere was somewhat different during the age of the dinosaurs, the nature of water vapor and the atmospheric processes that produce cumulus clouds have not changed with time.
Here's a dinosaur theorist talking about the sky during the Mezozoic era [no idea of his credentials]
This is not to say that the Sun and stars of the Mesozoic sky would look exactly the same as they do today. Astronomers are well aware of how atmospheric turbulence deflects starlight causing stars to twinkle. During the Mesozoic era, starlight passing through such a thick atmosphere would be thrown about so much by atmospheric turbulence that individual stars may not have been distinguishable. Likewise because of the extreme thickness of the atmosphere the Mesozoic Sun would probably appear slightly hazy in comparison to how it appears today.
The of course there's the post-asteroid impact about 65 million years back which made everything hazy twilight for a year or so.
posted by jessamyn at 7:36 PM on August 22, 2011 [6 favorites]

Response by poster: It hadn't occurred to me to wonder about cloud formation or the twinkling of stars, but now that you mention it, that's pretty fascinating, Jessamyn. :) Now I've got a couple of new rabbit holes to disappear down for the next half hour...
posted by waldo at 7:41 PM on August 22, 2011

So wouldn't the apparent color of the sky—to a human's perception—have changed along with it?

I don't see why it would have. Blue light would still have scattered more than other colours, hence the sky would have looked blue. Possibly if there were periods where there was a lot of volcanic dust in the air, then the sky would have looked redder.
posted by Dasein at 8:33 PM on August 22, 2011

The Earth only dates back about 4 billion years, and for the first part of its life there was no solid surface, no oceans, and no free oxygen in the atmosphere.

Once things cooled down, oceans formed, and then life formed and started doing photosynthesis and eventually spread all over the planet, you got the single biggest ecological change this planet has ever undergone: conversion of the atmosphere from reducing (hydrogen, methane, ammonia, water vapor) to what we now know (nitrogen, oxygen). I don't think anyone really knows how long that took, but it probably was millions of years.

That's when the sky started looking like it does now, except for the occasional year or two following a cosmic catastrophe.

(Dasein, are you aware that from the surface of Mars, the sky is orange?)
posted by Chocolate Pickle at 8:45 PM on August 22, 2011

Best answer: Relevant - It was probably orange before the great oxygenation event ~2.5B years ago.
posted by Long Way To Go at 11:26 PM on August 22, 2011 [1 favorite]

Best answer: I'd broadly agree with the points made above, except for a few major global catastrophes:

- The Great Oxygenation, 2.4 billion years ago, and the period before, as Long Way To Go has mentioned: the largest extinction event in Earth's history, when bacteria, over a period of thousands of years, made oxygen a primary component of the atmosphere. Before oxygen and nitrogen took over, the sky was possibly orange, as mentioned.
- The Permian-Triassic extinction, 250 million years ago. If a component of the extinction was the release of methane calthrates, as currently suspected, the sky may have had a green tint.
- the Toba supereruptions, approximately 77,000 years ago, together with the asteroid event that wiped out the dinosaurs: if the amount of dust and ash thrown into the air from a relatively small eruption like Krakatoa can color sunsets around the world for several years, the effect of these events on the perceived color of the sky would have been remarkable for decades afterwards: almost certainly red.

While your question isn't about the night sky, it's also notable that the Moon has been moving away from us at a steady rate of 3.8 centimeters per year: currently, its distance is an average of 384,403 km. While it doesn't directly effect the color of the sky, two billion years ago the moon would have been only 300,000 kilometers away, appearing nearly 50% larger (and even bigger still near the horizon, due to the moon illusion).
posted by Bora Horza Gobuchul at 12:22 AM on August 23, 2011 [18 favorites]

Response by poster: I like the answers to the questions I didn't ask even more than I like the answers to the question I did ask. Note to self: Be more vague with future AskMeFis. ;)
posted by waldo at 5:25 AM on August 23, 2011

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