- 4081 - EARTH MYSTERIES - why are we all wet? When the first Earth Day was held in 1970, geologists were still putting the finishing touches on plate tectonics, the model that explains how the Earth's surface takes shape. More than 40 years later, many riddles still remain when it comes to our planet.
------------------- 4081 - EARTH MYSTERIES - why are we all wet?
- Why are we all
wet? Scientists think Earth was a dry
rock after it coalesced 4.5 billion years ago. So where did this chemical, H2O,
come from? Perhaps an interstellar delivery system, in the form of massive
impacts about 4 billion years ago. Pummeled by icy asteroids, the Earth could
have replenished its water reservoirs during the period, called the “Late Heavy
Bombardment”.
-
- What's down there
in the core of the Earth? 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. The stuff of legend and lore, Earth's core
has long fascinated writers as well as scientists.
-
- For a while, the
composition of Earth's unreachable core was a solved mystery … at least in the
1940s. 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, they surmised.
-
- But 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.
-
- 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. 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.
- 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. 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.
-
- Where did all the
oxygen come from? 3.5-billion-year-old
fossil microbes. 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.
-
- 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.
-
- What caused the
Cambrian explosion? 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.
-
- 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.
-
- When did plate
tectonics start? 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. 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.
-
- Will we ever
predict earthquakes? 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.
-
- 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. 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.
-
- It seems that the
blueprint for complex brain development remains the same, despite 500 million
years of divergent evolution.
Scientists who watched nerve cells connect inside the eyes of growing
squid have uncovered a remarkable secret, the cephalopods’ brains independently
evolved to develop in the same way ours do.
-
- The discovery,
made using high-resolution cameras focused on the retinas of longfin squid
(Doryteuthis pealeii) embryos, reveals that, in spite of 500 million years of
divergent evolution, the basic blueprint for how complex brains and nervous
systems evolve may be the same across a wide range of species.
-
- The intelligence
of cephalopods, a class of marine animals that includes octopuses, squid and
cuttlefish, has long been a subject of fascination among biologists. Unlike
most invertebrates, these animals possess remarkable memories; use tools to
solve problems; excel at camouflage; react with curiosity, boredom or even
playful malevolence to their surroundings; and can dream, if the ripples of
colors that flash across their skin as they sleep are any indication.
-
- Octopuses may be
so terrifyingly smart because they share humans' genes for intelligence. To
study the squid embryos’ developing brains, the scientists used fluorescent
dyes to mark a special type of stem cell called neural progenitor cells, before
studying how they developed with regular, 10-minute snaps from microscope
cameras. The cameras looked at the retinas, where roughly two-thirds of a
squid's neural tissue is found.
-
- Just as in vertebrates,
the researchers saw the squids’ progenitor cells arrange themselves into a
structure called a pseudostratified epithelium, a long, densely packed
structure that forms as a crucial step in the growth of large, complex tissue.
The researchers noted that the size, organization and movement of the
structure's nucleus was remarkably similar to the same neural epitheliums in
vertebrates; something that was once considered a unique feature that enabled
back-boned animals to grow sophisticated brains and eyes.
-
- Much like humans,
octopuses and squid also have a large variety of microRNAs (small molecules
that control how genes are expressed) found inside their neural tissue. Just
how valuable it is to study the diversity of life. By studying this diversity, you can actually
really come back to fundamental ideas about even our own development and our
own biomedically relevant questions.
-
-
July 8, 2023 EARTH MYSTERIES
- why are we all wet? 4081
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