Where Did Earth’s Water Come From?

Anyone who’s ever seen a map or a globe easily knows that the surface of our planet is mostly covered by liquid water — about 71%, by most estimates* — and so it’s not surprising that all Earthly life as we know it depends, in some form or another, on water. (Our own bodies are composed of about 55-60% of the stuff.) But how did it get here in the first place? Based on current understanding of how the Solar System formed, primordial Earth couldn’t have developed with its own water supply; this close to the Sun there just wouldn’t have been enough water knocking about. Left to its own devices Earth should be a dry world, yet it’s not (thankfully for us and pretty much everything else living here.) So where did all the wet stuff come from?

As it turns out, Earth’s water probably wasn’t made, it was delivered. Check out the video above from MinuteEarth to learn more.

*71% of Earth’s surface, yes, but actually less total than you might think. Read more.

MinuteEarth (and MinutePhysics) is created by Henry Reich, with Alex Reich, Peter Reich, Emily Elert, and Ever Salazar. Music by Nathaniel Schroeder.

UPDATE March 2, 2014: recent studies support an “alien” origin of Earth’s water from meteorites, but perhaps much earlier in its formation rather than later. Read more from the Harvard Gazette here.

Jason Major

A graphic designer in Rhode Island, Jason writes about space exploration on his blog Lights In The Dark, Discovery News, and, of course, here on Universe Today. Ad astra!

View Comments

  • The video is nice. However, it is ignored or even refused the studies which expands the reservoir of Earth ocean-like water to include some comets. See the Nature paper "Ocean-like water in the Jupiter-family comet 103P/Hartley 2" by Hartogh etl al.

  • Have any studies been done that estimate how many meteorites it would have taken to deposit all of this water? While I realize that we are talking about a very long period of time, it would have taken an incredibly large number of meteorites to accomplish this.

    • The impact rate was substantially higher (and with larger impactors) early in Earth's history, and especially before about 3.9 billion years ago. While it's disputed whether there were particularly "heavy" periods of asteroid and comet bombardment, it is understood that the early Solar System was a tumultuous place.

  • "Solid particles" in the Solar System may have contributed to (water in the) oceans to some degree, also... (A piece of stone may include water...)
    The Earh was hot at the beginning.. But it had an "hot atmosphere" also...

  • How big did the planetesimals get prior to the start of fusion and the solar wind?
    Wouldn't the dust in the inner solar system have blocked most of the light/heat of the forming sun.
    Could the planetesimals have gotten large enough to contain water or form materials that lock in water prior to the solar wind?

    Water is not abundant as mentioned in the video. Its actually a very small fraction of the total mass/volume of the earth
    Only a tiny fraction would need to be locked away in planetesimals prior to nuclear fusion starting.

    • I guess the collapse rate of the dust cloud would determine how likely pre-fusion planetesimal formation would be, I doubt if it's possible to determine the temperature, mass etc. of a cloud based on the resulting star but some clever people might be able to do it from looking at open star clusters. I think the considerable violence of star birth would give planetesimals a hard time, but no reason why some wouldn't survive.

      The same treatment for Europa shows there was plenty in the solar system

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