Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Europan Ocean on 15/09/2019 17:20:02
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What would moon have looked like from Earth on a clear evening, 4 billion years ago? Was that not shortly before life formed on Earth?
It would have been extremely close! Immediately after it's formation from the Thea collision it must have resolved to a closest orbit, and moved away over time due to tides over millions of years?
At 4 billion years ago say 200 million years into it's life, the moon also had an atmosphere, coming from it's rocks and craters and internal sourced gases. What were those gases and what colours would they have been? And they would have been blowing in the solar wind, right? Under a dimmer colder sun?
The Earth at this time along the equator, would not have had any land not swept over by the tide during the week?
How many hours would a lunar orbit have taken back then? I can picture from above the swell up to the moon could have been tremendous. The point of centre of the two objects rotating would have been inside the Earth's diameter? Centrifugal forces would not have balanced out like with the Sun's gravity and the Earth's orbit? Or is there a solar tide?
I suppose then, to be safe from the tides, the best places to be would be by the poles? There was Gondwanaland at that time?
I am hoping some good ideas on this, I'd like to portray it.
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I'm not sure how long you would have to wait after the (hypothetical) impact before the Earth's surface was cool enough to stand on.
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This page goes into details about this very question: https://www.forbes.com/sites/quora/2018/07/11/what-did-the-moon-look-like-from-earth-4-billion-years-ago/#3cba74001151
These illustrations give visual comparisons of the Moon's appearance in the sky in the distant past: https://www.lpi.usra.edu/exploration/training/illustrations/earthMoon/
This calculator can tell you how long it took for the Moon to complete an orbit long ago: http://www.calctool.org/CALC/phys/astronomy/planet_orbit
At a distance of 15,000 kilometers, the Moon would have taken a bit over 5 hours to complete an orbit. At 20,000 kilometers, it's about 7.8 hours.
Given that most gases are colorless, Rayleigh scattering would have probably made the sky of the ancient Moon blue. It would have been darker than the Earth's sky, since it was a much thinner atmosphere (about 1% the pressure of Earth): http://www.astronomy.com/news/2017/10/moon-atmosphere
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Given that most gases are colorless, Rayleigh scattering would have probably made the sky of the ancient Moon blue. It would have been darker than the Earth's sky, since it was a much thinner atmosphere (about 1% the pressure of Earth): http://www.astronomy.com/news/2017/10/moon-atmosphere
The Earth's sky without Ozone would not have been blue?
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What would moon have looked like from Earth on a clear evening, 4 billion years ago? Was that not shortly before life formed on Earth?
Exact dates for both are not known, but it seems if life was barely there before the Theia event, that event would not have been kind to it. Maybe.. Life in general is impossibly resilient, and if such an impact should happen today, life would most likely survive it. Maybe life came from Theia itself. Think about it.
It would have been extremely close! Immediately after it's formation from the Thea collision it must have resolved to a closest orbit, and moved away over time due to tides over millions of years?
The third of Kryptid's links gives distances, but oddly enough, not length of day or month. I've heard the day would have been around 10 hours (and will be again if the sun can be prevented from swallowing us before then). The calculations can be done with conservation of angular momentum laws.
At 4 billion years ago say 200 million years into it's life, the moon also had an atmosphere, coming from it's rocks and craters and internal sourced gases. What were those gases and what colours would they have been? And they would have been blowing in the solar wind, right? Under a dimmer colder sun?
Solar wind might have blown that atmosphere away almost as fast as it was emitted from the rocks. Unclear if any appreciable pressure ever built up, but your subsequent link says yes, perhaps around 1% Earth's current pressure.
The Earth at this time along the equator, would not have had any land not swept over by the tide during the week?
Oceans took a long time to form after the Theia event. Don't think tides ever swept clean over the continents.
I've heard of weather forecasts for back then: Hurricanes with mercury pressure down to about 15 cm, strong enough to polish the landscape down to smooth rock.
How many hours would a lunar orbit have taken back then?
Right after the moon formed, less than a day. Several hundred million years later, maybe 4 days.
The point of centre of the two objects rotating would have been inside the Earth's diameter?
It still is, about 75% of the way to the surface. Yes, it would have been deeper in back then.
Centrifugal forces would not have balanced out like with the Sun's gravity and the Earth's orbit? Or is there a solar tide?
Don't know what you mean by centrifugal forces balancing out. I think the moon's acceleration on Earth might have been as strong that that of the sun at some point. It isn't close anymore. The Earth always accelerates towards the sun even when the moon is full, pulling hardest in the opposite direction. Yes, there have always been solar tides. You're very aware of them if you live at sea level.
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The Earth's sky without Ozone would not have been blue?
The ozone is not a major factor in the colour of the sky.
https://www.metoffice.gov.uk/weather/learn-about/weather/optical-effects/why-is-the-sky-blue
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https://www.lpi.usra.edu/exploration/training/illustrations/earthMoon/
This site say that the molten Moon was 16 times larger soon after Thea. This means 16 times the diameter - it would have been 250 times the area of sky.
However, the Earth' diameter is 3.7 times larger than the Moon, so the Earth would have taken up nearly 1000 times more of the Moon's sky than the Moon currently takes of the Earth's sky.
It is thought that the Moon became tidally locked early in its life.
Since the Earth was also molten, it is thought that the Earth's huge radiation output onto the Moon caused the difference between the near and far sides of the Moon - the near side has lots of large lava flows, which are absent on the far side of the Moon.