back to article Boffins blame meteorites for creating Earth's oldest rocks

The oldest rock formations on Earth were born when meteorites pummelled into the ground over four billion years ago, according to a Nature Geoscience paper published on Monday. A team of geologists have analysed samples of felsic rocks known for containing high concentrations of silica near the Acasta River near Great Bear …

  1. Anonymous Coward
    Anonymous Coward

    The headline picture for an article on rock around the world seems appropriately like water everywhere.

    1. DJV Silver badge

      Time for another bath then!

    2. Anonymous Coward
      Anonymous Coward

      Water, water, water everywhere!

      Thats hardly surprising as 70% of the Earth's surface is covered in water.

  2. SkippyBing Silver badge

    Confused

    Like the great Sheldon Lee Cooper I'm not a geologist, so could someone explain if the rock formations were formed by the 'melting of pre-existing iron-rich basaltic rock', how they can be the earliest?

    1. deadlockvictim Silver badge

      Re: Confused

      The rocks in the article are not the earliest rocks, they are the oldest known rocks which have survived. Any rock before that was presumed mined by aliens (presumably drinking Ol' Janx Spirit), subsumed into the earth's innards or hasn't been found yet.

    2. Anonymous Coward
      Anonymous Coward

      Re: Confused

      "how they can be the earliest?"

      I think what was meant was that they are (amongst) the earliest rocks for which we have evidence i.e. they still exist - any older rocks have been entirely reprocessed by erosion or complete remelting deep inside the Earth and no longer exist in any identifiable form.

      The Acasta Gneisses are not quite reckoned to be the oldest rocks - at ~4.4 Gy old zircons from the Jack Hills in Australia are older, but they are believed to be the oldest exposed rocks.

      What bothers me about the hypotheses is that metamorphic rocks are formed under both temperature and pressure, with pressure seeming to play a greater part - Wikipedia says that the temperatures just need to be greater than 150-200C (the original rock doesn't need to be remelted to be transformed to metamorphic rock) but the pressures need to be greater than 100 megapascals (1,000 bar). Now whilst a meteorite impact will create great pressure, it will be in the form of a brief shock wave, which will have more of a brisant shattering effect than a compressing effect, and indeed, it is these shattering effects, such as 'shatter cones' and 'shocked quartz' that are regarded as proof of an impact.

      Another problem is that whilst an impact event could certainly produce temperatures high enough to remelt surface rocks it would also mix them all up in that melting but all the pics of Acasta Gneiss that I've seen show some banding, which suggests that they weren't mixed up - the stratification appears to have been preserved.

      1. bombastic bob Silver badge
        Devil

        Re: Confused

        wasn't the entire earth formed by a bunch of dirt, dust, and rocks colliding and collecting together to form a gravity well, and eventually the planet? So what's the point, here?

        So yeah EVERYTHING was once 'a meteor'

        I'm also not really happy with uranium vs lead isotopic dating. It more or less assumes that the lead content came entirely from the uranium. Unless we have a baseline of the content ratio from the exploding star that probably created it, you can only guess.

  3. mickaroo
    Coat

    Pedant Alert

    Please...

    A team (of geologists) has analyzed samples...

    Wears my coat...?

    1. Julian Bradfield

      Re: Pedant Alert

      In British English (and many other sensible languages, including even classical Latin), a collective noun can take either singular or plural concord, according as you're thinking of it as a single entity or the sum of its members.

    2. Alister Silver badge

      Re: Pedant Alert

      Wears my coat...?

      What does?

      1. The Oncoming Scorn Silver badge
        Joke

        Re: Pedant Alert

        Two nuns in the bath, one says to the other "Wheres the soap?"

        "Yes it does rather!"

    3. John Brown (no body) Silver badge

      Re: Pedant Alert

      "A team (of geologists) has analyzed samples..."

      Of course. As any fule knows, it's not a team, it's a gaggle of geologist.

    4. deadlockvictim Silver badge

      Re: Pedant Alert

      There is also a clue with the indefinite article.

      'A team' must be grammatically singular, regardless of whether it is composed of many individuals.

      1. Alister Silver badge

        Re: Pedant Alert

        'A team' must be grammatically singular, regardless of whether it is composed of many individuals.

        Whilst that may be true by American convention, it is definitely not the case for British English.

        As this is still a British website (just about) then British rules win...

        1. bombastic bob Silver badge
          Devil

          Re: Pedant Alert

          I didn't know British singular/plural grammar rules were any different...

          (as long as the 'singular they' isn't used, I'm ok with it)

        2. deadlockvictim Silver badge

          Re: Pedant Alert

          You and Ms. Quach are wrong.

          A team has... is correct.

          A team have... is incorrect.

          This is primary school [2] English.

          A team [1] has analysed samples of felsic rocks known for containing high concentrations of silica near the Acasta River near Great Bear Lake, the largest lake in Canada.

          [1] A team of geologists.

          [2] I'm not sure what it's called in the States: K12? grade school?

          1. Alister Silver badge

            Re: Pedant Alert

            Interesting. What's your reaction to these examples?

            Arsenal have won the FA Cup more times than any other team.

            The Chicago Bears has never played in the FA Cup.

  4. Anonymous Coward
    Anonymous Coward

    Sounds like the blurb for new book

    Attacked by marauding barbarians

    "known as the Idiwhaa gneisses, meaning ancient in the Dogrib language spoken by the Tlicho people"

    a young girl and her pet chewna are the only survivors. Together they must......

  5. The Nazz Silver badge

    OK, come on folks ...

    who's nicked Lake Superior?

    There's a clue in it's name.

    1. Michael Wojcik Silver badge

      Re: OK, come on folks ...

      Less than half of Lake Superior is Canadian territory, so it's the largest lake partly in Canada.

      That said, Superior has more than twice the surface area of Great Bear, and I don't know precisely how much is Canadian (didn't find it in a quick search and I'm too lazy to do more). So there may yet be more Superior in Canada than there is Great Bear.

  6. Roj Blake Silver badge

    Partridge

    Am I alone in reading the byline in the voice of Alan Partridge during his Toblerone addiction?

  7. 89724102172714182892114I7551670349743096734346773478647892349863592355648544996312855148587659264921

    Uranus is too crusty for pummelling

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