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Many of the celestial bodies in our solar system have well-established color schemes, at least in the minds of the public. Mars is pale-red and black, Venus (beneath the clouds) is generally shown in rich yellows and oranges, the Moon ranges from dark to light gray, etc.

And, of course, Earth is famously blue and green. However, this is entirely because of the presence of large oceans and life. We're not seeing Earth's geology represented in these colors, as we are with the other planets, we're seeing overlaid colors from other processes that don't apply to Mars, Venus, or the Moon.

So I'm wondering, if you stripped away life and the oceans, what color(s) would Earth be? Based on types of rock, etc. Would the seabed be a different color from the continents? Would it be more uniform, or would it vary in color quite a bit from region to region? Would it be a similar gray to the Moon, or would other chemical processes (like the rusting of Mars) give it a more unique palette?

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  • $\begingroup$ The earth is "blue" because of the atmosphere and Rayleigh Scattering... not the ocean. Water is not blue... it is clear. $\endgroup$
    – f.thorpe ♦
    Aug 20, 2015 at 14:39
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    $\begingroup$ No, @farrenthorpe, water is blue. You can read all about it. You're thinking of why the SKY is blue, which is Rayleigh Scattering. The reason the Earth is described as blue is because of the large oceans on its surface, which are blue. $\endgroup$
    – Nerrolken
    Aug 20, 2015 at 15:03
  • $\begingroup$ The link says " Lakes and oceans appear blue for several reasons. One is that the surface of the water reflects the color of the sky. While this reflection contributes to the observed color, it is not the sole reason." I oversimplified the processes... thank you for linking to them. My point is that "Earth is famously blue and green. However, this is entirely because of the presence of large oceans and life." is not true. Light scattering and absorption is key to this question in both air and water. physics.stackexchange.com/questions/35882/… $\endgroup$
    – f.thorpe ♦
    Aug 20, 2015 at 19:04
  • $\begingroup$ @farrenthorpe It also says "the blue hue of water is an intrinsic property" right at the top, but either way, it's a distinction without a difference. "Earth is blue because it has water" and "Earth is blue because the water covering much of Earth's surface scatters certain wavelengths of light" are functionally the same thing. My question remains: without water and life, what color would our planet be? What are the main colors of the surface rock on planet Earth? $\endgroup$
    – Nerrolken
    Aug 20, 2015 at 20:12
  • $\begingroup$ The oceans used to be redish/brown due to dissolved Iron, prior to photosynthesis creating free oxygen which took the Iron out of the oceans. The land, without life, probably would look similar to the moon, and we might think of the moon as bright cause it looks bright in the sky, but it's actually darkish. Without life, the Earth wouldn't be very pretty. But also, without carbon (CO2) capture, the atmosphere would likely be thicker, hotter and hazy, might look similarish to Venus from above. One big cloud. $\endgroup$
    – userLTK
    Aug 20, 2015 at 22:54

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That's actually an interesting question. Let's try to answer it, but first let's make a few assumption.

  • Oxygen on Earth is biogenic, so without life there would be no oxygen. However, let's assume that some magical process keeps the oxygen in the atmosphere.
  • Oceans play an important role in plate tectonics, and without it it might change. Let's assume that plate tectonics keep on running regardless of the state of the oceans.

The majority of the Earth's surface is covered by oceanic crust. This crust is composed of basalt, an iron rich rock. This iron would rapidly oxidise and rust, giving a red tint (possibly Mars-like) to most of the Earth's surface. The mid ocean ridges will most likely be black, but it will get redder the farther you get away from there.

The continental crust would like slightly different. Mountain ranges would appear grey, perhaps slightly pinkish - not too different from the highest peaks you see today. Most of the continental crust is composed of granite (sensu lato), a grey-pinkish rocks. Because there's no life and no vegetation, that barren landscape you see high above the mountains would go all the way down to the base of them mountains. At the mountain's base, you would get deserts of quartz sand, slightly yellow. Think the sand dunes of the Sahara desert. This sand comes from the breakdown of the granites. Quartz, the most resistant mineral in the granite forms sand, I guess from the action of wind. The other minerals (mostly feldspar) break down to form all kinds of clays, aka dust.

So to sum it up:

Most of the surface will be covered by dark red low lands, with high lands of sandy desert and Himalaya type mountain belts sticking out of them.

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    $\begingroup$ For anyone interested, I found a picture that roughly fits this description of the reddish rock of Earth. $\endgroup$
    – Nerrolken
    Sep 3, 2015 at 17:09
  • $\begingroup$ Interesting pic, but what is that white stuff around the South Pole? No water = no Antarctic ice (whatever "Antarctic" means if there are no humans around to coin that term). $\endgroup$
    – Oscar Lanzi
    May 2, 2021 at 0:54

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