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Can you find the Earth in this picture? (1990)
Mostly Harmless
It's not rocket science, it's...
The Final Frontier
The abyss stares back

Earth (Latin: Terra) is one of eight[note 1] planets (specifically, a rocky one due to its solid surface, as with the rest of the first four planets, though the majority of the rock on our own planet is underwater) in the solar system orbiting a star, sometimes called Sol in random science fiction stories. While some believe there is intelligent life on Earth, others are too smart to really believe this.

Earth is also one of the four fundamental elements the Greeks philosophized about, the others being water, air and fire. Some people consider their philosophical ruminations to be somewhat naive. If you consider that they were doing said philosophizing a good few thousand years ago, and the four elements line up pretty well with solid, liquid, gas and plasma, perhaps they were not too far off the mark after all.

Fun facts about the Earth[edit]

  • Most of its inhabitants believe that the Earth is an oblate spheroid, a sphere just slightly appearing to have been "pushed in" a bit on the poles so the equator "bulges out" a bit more than on a perfectly spherical object. A highly vocal, loony, and nasally minority seem to think that it is flat, presumably squarish. This RationalWiki editor believes that it is a icosahedron.
  • Despite the fact that "Earth" means dirt, most of Earth's surface is covered by water. Curiously, while water is absolutely vital to continued life as humans know it, most of the Earth's water, if consumed in sufficient quantities, would kill humans.
  • The Earth's environment is seemingly quite fragile. However, since it is our God-given right to trash it[note 2], dammit we're gonna do it.
  • Everyone that has ever lived and everyone you have ever known has been from Earth. Deep, ain't it? Alien abductionists may disagree with this.
  • Earth's star, Sol (though possession probably should belong to Sol and not Earth), is considered to be average as stars go. How's that for weird?
  • Earth lost out to Mars when all of the planetary bodies of the Solar System voted for Most Likely to Support Life. But, who's laughing now?
  • It is the only planet in the solar system not named after a Roman god / goddess in the English language.[note 3] However, the dwarf planets Haumea and Makemake are named after Hawaiian and Easter Island deities respectively, whilst Eris is named after the Greek goddess of discord.
  • It is the only known planet with RationalWiki, Minecraft, and feminism
  • It is also the only known planet with MRAs, the Religious Right and Scientology.
  • Its inhabitants are "Mostly Harmless"(caps intentional)
  • It has yet to create a sustainable civilization.[1][note 4]
  • Intelligent life is rather rare on earth.[2][3][4][5][6][7]

Quantitative facts about the Earth[edit]

  • Radius (volumetric mean) = 6371.0 km
    • Equatorial = 6378.1 km
    • Polar = 6356.8 km
    • Crust depth = 25 km (variable)
    • Mantle thickness = 2860 km
    • Core = 3480 km
  • Mass = 5.97×1024 kg
    • Atmosphere = 5.1×1018 kg
    • Hydrosphere = 1.4×1021 kg
    • Crust = 3.4×1022 kg
    • Mantle = 4.0×1024 kg
    • Core = 1.9×1024 kg
  • Distance from the Sun = 1.50×1011 m
  • Distance from the Moon = 3.84×108 m
  • Escape velocity = 11.186 km/s
  • Bond albedo = 0.306
  • Surface temperature = 288 K
  • Gravitational binding energy = 2.5×1032 J
  • Moment of inertia = 8.02×1037 kg m2
  • Density = 5514.8 kg/m3
    • Atmosphere (surface) = 1.217 kg/m3
    • Crust = 2700 kg/m3
    • Mantle = 4500 kg/m3
    • Core = 1.1E4 kg/m3


Unless someone gets it right much earlier, it's expected that the increase of the Sun's luminosity as it ages will cause an increased weathering of minerals, lowering atmospheric CO2 concentrations so much that in around 600 million years plants will begin to disappear as they will be unable to use photosynthesis.[8] No plants means no animals, and in roughly 1 billion years from now just bacteria will remain. Meanwhile, that very same increasing luminosity will also mess with the Earth's climate causing a moist greenhouse and the evaporation of the oceans, leaving Earth as a pink and brown bone-dry wasteland with dunefields on its equator, salt-rich flats with scattered ponds marking the former place of the oceans, an oxygen-rich, Venus-like crushing, atmosphere, and most of the little water just at the poles, this assuming there's not a runaway greenhouse effect that will render Earth a Venus-like planet or much worse if the oceans do not evaporate fast enough.

Given that no oceans means no plate tectonics heat may accumulate on Earth's interior until, as is thought to have happened in Venus, the planet's surface is covered in lava by extensive volcanism killing whatever managed to survive by then. Alternatively, if plate tectonics stopped before the loss of oceans erosion could transform Earth into a water-covered planet at least for a while.

Temperatures will eventually be so hot that the remaining life is expected to become extinct 2.8 billion years from now[8]. It's also expected that Earth' magnetic field will go away within a similar timeframe and that, if you had not enough, Moon's recession may cause the Earth's obliquity to go nuts within a similar amount of time, leaving a dead planet in all senses behind except for some large volcanoes over mantle hotspots[8].

Nothing more of interest except temperatures keeping its rise as the Sun evolves[note 5] is thought that will happen for some more billions of years until the Sun exhausts its hydrogen five billion years from now and goes full red giant 2.6 billion years later, moment in which it will absorb Earth but not before causing it to become a hell of a planet[8].

See also[edit]


  1. See the IAU's definition of what a planet is.
  2. Just ask former U.S. Secretary of the Interior James Watt
  3. For the sake of gratuitous pedantry, the names are in the Latin language, and borrowed into English. And technically, Uranus was a figure from Greek mythology, not Roman; his equivalent in Roman mythology was Caelus.
  4. For the record, a civilization becomes sustainable when it reaches Type I on the Kardashev scale, which, if they don't wipe ourselves out, should happen by 2200 CE. Pre-industrial Type 0 civilizations have a good chance of being wiped out by outside forces, while industrial/post-industrial Type 0 civilizations such as theirs have a good chance of wiping themselves out, especially when they inevitably discover that E=mc2.
  5. Some calculations give a very small probability of Mercury's orbit going haywire sometime in the next billion years and crashing into another Solar System planet. While at first it was thought it could crash into Earth, [later studies] show that will not happen