- 3995 - EARTH - mysteries remain? - Many riddles still remain when it comes to our planet. Here are some of Earth's biggest unsolved mysteries.
--------------------------- 3995 - EARTH - mysteries remain?
- Why are we all wet? Scientists think Earth was a dry rock after
it coalesced 4.5 billion years ago. So where did this essential chemical, H2O,
come from? Perhaps an interstellar delivery system, in the form of massive impacts
about 4 billion years ago.
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- Pummeled by icy asteroids, the Earth could
have replenished its water reservoirs during the period, called the “Late Heavy
Bombardment”. But the beginnings of Earth's water are shrouded in mystery
because so little rock evidence remains from this time period.
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- What's down there in the core? The xenon gas missing from Earth's
atmosphere might have been found. Scientists say it is stuck in Earth's core,
where the noble gas is bound with other atoms
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- With meteorites as proxy, scientists gauged
the planet's original balance of essential minerals, and noted which were
missing. The iron and nickel absent in Earth's crust must be in the core.
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- Gravity measurements in the 1950s revealed
those estimates were incorrect. The core was too light. Today, researchers
continue to guess at which elements account for the density deficit beneath our
feet. They're also puzzled by the periodic reversals in Earth's magnetic field,
which is generated by the outer core's flowing liquid iron.
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- How did the moon get here? Did a titanic collision between the Earth and
a Mars-size protoplanet form the moon? There's no universal consensus on this
giant impactor theory, because some details don't pan out.
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- For example, the chemical composition of
both rocky bodies matches so closely it suggests the moon was born from Earth,
not a separate impactor. But a fast-spinning young Earth could have flung off
enough molten rock during impact to form a chemically similar moon, other
models suggest.
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- Where did life come from? Was life brewed on Earth or sparked in
interstellar space and delivered here on meteorites? The most basic life
components, such as amino acids and vitamins, have been found on ice grains inside
asteroids and in the most extreme environments on Earth.
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- Figuring out how these parts combined to
form the first life is one of biology's biggest hurdles. And no direct fossil
traces of Earth's first inhabitants, which were probably primitive,
rock-chewing bacteria, have yet been found.
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- Fossils of 3.5-billion-year-old microbial
communities were discovered in Australia. We owe our existence to
cyanobacteria, microscopic creatures that helped to radically transform Earth's
atmosphere. They pumped out oxygen as waste, and filled the skies with oxygen
for the first time about 2.4 billion years ago.
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- But rocks reveal oxygen levels cruised up
and down like a roller coaster for 3 billion years, until they stabilized
around the Cambrian Period about 541 million years ago. So did bacteria spike
the air, or was there another contributing factor? Understanding the shift to
an oxygen-rich Earth is a key factor in decoding the history of life on our
planet.
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- What caused the Cambrian explosion? Arthropods from the Burgess shale, such as
the trilobite Olenoides and a chelicerate called Sidneyia, exploded in
morphological diversity following the so-called Cambrian Explosion.
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- The appearance of complex life in the
Cambrian, after 4 billion years of Earth history, marks a unique turning point.
Suddenly there were animals with brains and blood vessels, eyes and hearts, all
evolving more quickly than during any other planetary era known today.
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- A jump in oxygen levels just before this
Cambrian explosion has been offered as explanation, but other factors could
explain the mysterious rise of the animals, such as the arms race between
predator and prey.
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- Thin plates of hardened crust knocking
about Earth's surface make for beautiful mountain sunsets and violent volcanic
eruptions. Yet geologists still don't know when the plate tectonics engine
revved up.
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- Most of the evidence has been destroyed.
Just a handful of tiny mineral grains called zircons survive from 4.4 billion
years ago, and they tell scientists the first continental-like rocks already
existed. But the evidence for early plate tectonics is controversial. And
geologists still wonder how continental crust forms.
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- At
best, statistical models can tease out a forecast of future earthquake
probability, similar to weather experts who warn of coming rain. But that
hasn't kept people from trying to predict when the next one will hit, with no
success.
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- Even the biggest experiment failed by 12
years, when geologists predicted an earthquake at Parkfield, Calif., by 1994,
and set up instruments to catch the coming temblor. The actual quake hit in
2004.
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- One of the biggest hurdles is that
geologists still don't understand why earthquakes start and stop. But there
have been advances in predicting aftershocks and manmade earthquakes, such as
those linked to wastewater injection wells (as used in fracking).
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May 12, 2023
EARTH - mysteries remain? 3995
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