- 4337 - LIFE ON EARTH and MARS? We Owe Our Lives to the Moon. Life appeared on Earth through a series of lucky coincidences, and that luck started with our Moon. None of the other planets of the inner solar system have significant moons.
------------------------- 4337 - LIFE ON EARTH and MARS?
- Space is lonely around Mercury and Venus.
Mars does have two small moons, Phobos and Deimos, but those are simply
captured asteroids, lassoed in the not-too-distant past and doomed to
eventually come close enough to their unloving parent to be torn to shreds by
gravitational forces.
-
- No other planet in the solar system, or any
exoplanet known orbiting other stars, has a moon quite like the Moon. With the
exception of Pluto and its companion Charon, no other planet has a satellite
with the relative mass of our Moon.
-
- The giant worlds like Jupiter and Saturn
have some moons large enough to be planets in their own right, but they are
insignificant next to the massive bulk of their parents. The Moon is roughly 1%
the mass of the Earth, a percentage unheard of in the galaxy.
-
- We found ourselves with our satellite
through the chance encounter of a violent collision. Billions of years ago,
when our solar system was but a churning mass of gas and dust swirling around a young star, the planets began to coalesce.
But before they could become planets, they were mere planetesimals,
agglomerations of rock and ice, dozens of them swarming in the chaos of those
early days.
-
- In the orbit of what would one day become
the Earth, we were not alone. At some point, due to some accident of trajectory
and conceit of momentum, a planetesimal the size of Mars struck us. The details
of the collision and its aftermath are muddied; with no time machine we can
only rely on computer simulations of the impact. But this much is clear: the
cosmic accident vaporized part of the Earth and its impactor, creating a ring
of superheated plasma that looked more like a rage-filled donut than a proto-world.
-
- With time the fury ceased; the plasma
cooled. The ring coalesced back into the shape of a sphere, but now with an
orbiting companion. The traces of the impactor are almost lost to us, the
evidence of its existence only slim. The Earth contains more heavy metals in
its core than it should for a planet its size.
-
- And the Moon itself, when sampled to
measure the composition of its fundamental elements, reveals itself to be made
of the exact same mixture as the Earth. A common origin then, not an object
formed elsewhere and captured by our gravity.
-
- Day to day, the Moon doesn’t largely affect
the Earth. It raises and lowers the tides in its month-long orbit, sharing the
duty with the gravitational pull of the Sun itself. Some creatures, like dung beetles,
use the polarized light of the Moon to guide their way back home after a night
of collecting. But otherwise our satellite does nothing more than give us
something beautiful to look it.
-
- Our planet spins about its axis, but that
spin is tilted with respect to the movement of the Earth in orbit around the
Sun by 23 and a half degrees. This tilt gives us our seasons, with half our
year spent with the northern pole facing the Sun, and the other half trading
places with the southern pole.
-
- Our planet could have had any orientation it
wished. The other planets have lesser and greater tilts, with Uranus tipped
completely over on its side and Venus rotating backwards. And there’s nothing
to keep that tilt fixed over cosmic time. Our planet was born spinning, but the
internal arrangements of its core, mantle, and crust, along with the
ever-present gravitational machinations of Jupiter, can cause the Earth to
wobble, shifting its tilt ever so slightly.
-
- With every shift in the tilt, the seasons
would radically change. Instead of regular, predictable changes year after
year, we would experience ages with endless summers, or ages with violent but
short winters, or anything in between. The rhythm of the seasons provides a
pulse for life, which has the freedom to grow and evolve without trying to
overcome great climactic shifts caused by a changing axis.
-
- The Moon acts as a great gravitational
counterweight, stabilizing the motion of the Earth. By providing a source of
gravity external to our planet, the Earth’s interior is free to shift and
reconfigure.
-
- Earth's magnetic poles completely flip. We sit at just the right distance from our
sun for liquid water to exist on the planet's surface. The gravitational pull
of other large planets helps protect us from apocalyptic collisions with
wandering meteorites. And the planet's magnetic field encircles Earth with a
protective barrier that shields us from charged particles hurtling through
space.
-
- Earth's magnetic field is generated by the
complex flow of molten metallic material in the outer core of the planet. The
flow of this material is affected both by the rotation of Earth and the
presence of a solid iron core, which results in a dipolar magnetic field where
the axis roughly aligns with the rotational axis of the planet.
-
- Hidden in the chemical composition of
ancient rocks are clues that Earth's magnetic field is a dynamic, shifting
phenomena. Cooling magma rich in iron minerals is pulled into alignment with
Earth's magnetic field, similar to how a needle is pulled to point towards
north on a compass. The study of ancient geomagnetic fields recorded in rocks
is the subject of a discipline known as "paleomagnetism."
-
- Paleomagnetic research has provided
scientists with the knowledge that Earth's magnetic field has shifted and even
reversed in polarity many times in the geological past.
-
- Earth's magnetic field varies at very short
timescales and extremely long ones, ranging from milliseconds to millions of
years. The interaction of the magnetic field with charged particles in space
can alter it at short timescales, while perturbations in the magnetic field at
longer timescales are caused by internal processes unfolding in the outer
liquid core of the Earth.
-
- Fluctuations in the magnetic field caused
by the movement of metallic material in the outer core have brought about full
reversals of the magnetic field's polarity in Earth's past.
-
- Paleomagnetic studies which have studied
previous states of the magnetic field have shown there are two possible states
of polarity, the current 'normal' state, where the lines of force of the field
enter towards the center of the Earth in the northern hemisphere and exit
towards the outside of the Earth in the southern hemisphere. The inverse, or
'reverse' polarity is also equally as probable and stable.
-
- Paleomagnetic studies have shown that
polarity reversals of Earth's magnetic field are not periodic and cannot be
predicted. This is largely because of the behavior of the mechanisms that are
responsible for it.
-
- The flow of the metallic fluid which is
mostly molten iron, in the outer core of the Earth is chaotic and turbulent.
Polarity reversals occur during periods of low geomagnetic field intensitey
-
- The transitory period of polarity reversal
appears as a geologically instantaneous, with a duration spanning up to a few
thousand years.
-
- When the magnetic field is prone to
flipping, it is in a state of reduced intensity, resulting in a greater
exposure of Earth's atmosphere to solar wind and cosmic rays in the form of
charged particles. During the “Laschamps excursion”, a recent period of low
magnetic field intensity which occurred only 41,000 years ago, the global
cosmic ray flux reaching the Earth's atmosphere was up to three times higher
than today's value.
-
- There is no significant evidence of a
correlation between mass extinctions of life on Earth and geomagnetic polarity
reversals. However, linking rates of species extinction and with periods of low
magnetic field intensity is hindered by uncertainties in the known timescale of
these magnetic 'flips'.
-
- Magnetic reversals happen frequently on
geological timescales (several hundred times in the past 160 million years),
while recorded mass extinction events occur every hundred million years or so
(much less frequently).
-
- In terms of human civilization, it is not
the shifting of the magnetic poles that is directly concerning, but the
resulting period of reduced geomagnetic field intensity. Society is growing
increasingly reliant on technology, and the effects of a reduced magnetic field
intensity should be seriously considered.
-
- The risks to which our planet and
civilization is exposed could have significant impacts on civil society, how we
do commerce, security, communications, power infrastructure, satellites and the
lives of people in low Earth orbit.
-
- Unfortunately, the sporadic nature of
magnetic variations and reversals means we cannot predict when exactly this
will happen, all we know is that it will happen someday.
-
-
February 2, 2023 LIFE ON EARTH and MARS 4337
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--------------------- --- Friday, February 2,
2024
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