- 4632 - EARTH WATER WORLD ? Our planet started off bone dry. Then space sent ice balls and 'water balloons' to give us water. Each time you take a sip of water, you’re imbibing liquid that, in all likelihood, is up to 4.5 billion years old. Earth is awash in a life-sustaining substance about as ancient as the planet itself.
------------------------------------------------ 4632 - EARTH WATER WORLD ?
- Astrophysicists don’t completely know
where the stuff came from, but circumstantial evidence suggests that
water-containing meteorites might have pummeled an infant Earth. Those rocky
showers would have helped transform a bone-dry place into a unique wet world.
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- Although our planet is covered by an
estimated 326 quintillion gallons of H2O, it’s drier than you’d imagine
comparing Earth, which could be as little as 0.023 percent water, to crackers,
which are around 2 percent water. That’s still a lot more moisture than we had
at the beginning.
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- When the solar system first came together,
some of the young planets were too hot for water. Earth and Mars should have
formed extremely dry due to their locations in the solar system’s frost line.
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- When the sun was coalescing out of a
collapsing cloud of gas and dust 4.6 billion years ago, its tremendous heat
made a boundary. Outside of it, space was cool enough for ice grains to
solidify. This helps explain why far-out
Jupiter and Saturn have ocean moons.
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- Inside of it, heat vaporized water. Earth
and the other inner planets clumped together from the dry rock and dense metal
that remained. Something must have happened, some millions of years later, to
nourish those planets with water. Astronomers have explored several possible
scenarios.
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- Craters on the surface of our moon indicate
that our side of the frost line was constantly hit with space rocks, including
a particularly violent shower known as the “Late Heavy Bombardment”. Some
experts think those projectiles, specifically meteorites, the bits of asteroids
that fall to Earth, might have been more like cosmic water balloons.
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- This hypothesis is supported by the 2010
discovery of a thin crust of frost on asteroid “24 Themis”. NASA found water-bearing clay minerals in
the near-Earth asteroid “Bennu” during a ground-breaking sample-retrieval
mission.
-
- Still, it’s possible that other processes
were involved in delivering water to Earth, such as gas from the cloudy solar
nebula that dissolved hydrogen into the planet’s magma layer. It’s also
possible that there were multiple sources and steps.
-
- The pieces of the puzzle are not
clear. One major clue that gives us an
idea of where the water may be coming from is the type of hydrogen that flows
through our aquatic systems.
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- The most common form of hydrogen in the
universe has a lone proton orbited by an electron. But there’s a slightly
different version called “deuterium” with a proton and a neutron squished into
the center. Astronomers have measured the proportion of deuterium to regular
hydrogen in Earth’s water and looked for that “D-H ratio” in other objects
around the solar system.
-
- “Carbonaceous chondrites”, a kind of
meteorite, are a pretty good D-H ratio match. If our solar system was once an
ancient construction site, think of the chondrites as the unmelted rubble. They
hail from the asteroid belt’s outer section, closer to Jupiter than Mars, which
means they probably formed on the wet side of the frost line.
-
- A single ton of carbonaceous space rocks,
rich in ice and watery minerals, could have delivered 110 to 220 pounds of
water to Earth. When Jupiter and Saturn’s masses grew big really fast, the gas
giant kicked those rocks toward the sun and the inner planets.
-
- The meteorites “contain a lot of organic
goop” like carbon and other molecules associated with life. They also hold
volatile materials, substances that evaporate easily when heated, like water,
zinc, and hydrogen from the early days of the solar system. While those can be
found on our planet today, a few volatile materials are still missing.
-
- If the carbonaceous chondrites contributed
Earth’s water, they would have also contributed Earth’s noble gasses. But they don’t support those elements, so
something else must have filled the gap. “Comet 67P”, closely studied in the
mid-2010s has the right noble gas content.
-
- This lends to the idea that a bunch of
space bodies hit Earth with noble gasses, H2O. If most of the water gets
contributed by asteroid impacts and most of the noble gasses are contributed by
comets. Newer evidence emphasizes a
different kind of space rock from closer to home.
-
- “Enstatite chondrites” are meteorites with
a similar composition to the original building blocks of Earth. Because they
formed within the inner solar system, on our side of the asteroid belt,
astronomers classify them as “non-carbonaceous.” While they don’t have as much
water as their distant counterparts, they could pack some punch.
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- A suite of more recent studies have
linked nitrogen and other volatile elements on Earth to enstatite
chondrites. Sn analysis of Martian
zinc, indicates that debris from the inner solar system transported the metal
to our neighbor. If zinc existed within those meteorites, they probably carried
other volatile materials, specifically, water. Mars had liquid water at one
point and may have some still lurking under an ice cap.
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- If space rocks brought water to the Red
Planet, could they have done so elsewhere?
What we’re learning here may not only be applicable to our understanding
of what we should expect on Mars, but
about the possibility of water and organic molecules being delivered to planets
around other stars, which would give you an environment that could be conducive
to the formation of life.
-
- Putting these lines of evidence together
gives us a recipe that would have involved lots of damp local rocks and a few
of the more distant ice balls. Hydrogen, nitrogen, and zinc isotopes “all tell
the same story” of a wet Earth.
Previously overlooked non-carbonaceous meteorites probably supplied
about 70 percent of the planet’s water, and just a dash of carbonaceous
meteorites touched up its vast blue surface.
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-
December 2, 2024 EARTH WATER
WORLD ? 4632
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--------------------- --- Tuesday, December 3,
2024
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