What’s So Special About Earth?
Earth is our home. It’s where life as we know it has thrived. But there are countless
other planets in the universe - with up to 100 billion in just the Milky Way Galaxy alone
- so why are we on this one? What makes our planet so seemingly unlike any other?
This is Unveiled and today we’re answering the extraordinary question; What’s so special
about Earth?
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Of all the planets we’re aware of, Earth is unique and distinctive. Many other worlds
- in our own solar system or beyond - are too hot, too cold, too dry, barren, big or
small to support life. Others lack an atmosphere, a magnetosphere or a reliable orbit. Earth,
as it turns out, is just about right in nearly every domain. And these aspects come together
to produce something amazing - life where there was none before. You could even say
that, over the course of history, our planet has “come alive”. Which, by all accounts,
is pretty special!
Today, when we consider the possibility of life elsewhere in the universe, and indeed
try to search for it, we first have to understand the incredibly unlikely set of circumstances
that allowed us to thrive in the first place; here, in our particular place in the solar
system, in our particular galaxy. It’s the result of some amazing fortune and interplay
between a number of things.
Earth is in part special because of its place and order alongside it’s neighbouring planets.
First, our planet exists in balance with all the others; there are no planetary collisions
on the horizon, while the solar system’s larger bodies have actually helped to shield
us from all manner of asteroids and space debris in the past. Second, and more importantly
still, Earth is in the habitable or “goldilocks” zone of our solar system; it’s far away
enough from our sun to sustain liquid water, while not being too far to freeze it. When
scientists look for other planets with life, one of the first checks they do is to determine
whether it, too, is in a comparable position around its star. The condition of the star
plays a major role, though. The hotter the star, for example, the farther out a potentially
hospitable planet needs to be. Earth is in the right place for our specific sun, although
it’s also helped by another vital part of its makeup; its atmosphere!
Earth’s atmosphere helps to regulate its temperature, keeping us safe. It’s rare
because it’s mainly composed of nitrogen and oxygen - the element that gives us life.
But much of the reason why Earth can even maintain its atmosphere at all is because
it’s exactly the right size to do so; it exerts just the right amount of gravitational
pull - another crucial, cosmological lucky break.
The atmospheres of a lot of other planets are often composed of the most abundant elements
available, hydrogen and helium, or a large amount of carbon dioxide; neither of which
are all that helpful in supporting life. A few atmospheric tweaks in a couple of different
directions, then, and Earth could well have wound up with boiling surface temperatures
similar to Venus or choked of its potential as per Mars. In fact, early in Earth’s life,
its atmosphere actually was something like this. It was composed of mainly hydrogen and
helium but, again mostly due to Earth’s size, those elements eventually drifted away.
Then came a unique sequence in our planet’s ancient history where it effectively built
and perfected the favourable conditions we experience today.
As a volcanically active planet, Earth spent millions of years “spitting out” large
amounts of carbon dioxide and ammonia… all while its oceans set to work absorbing most
of the CO2. The leftover ammonia was then broken down by the sun’s ultraviolet rays,
leaving Earth bathed in nitrogen and hydrogen (the latter of which drifted away once more).
Over time, as plant life developed, even more of the CO2 was sifted from the atmosphere,
but now it was getting turned into oxygen via photosynthesis. And then the path was
clear for intelligent life to emerge.
The formation of our atmosphere is impressive enough on its own, but it too wouldn’t have
been possible were it not for other factors - especially the precise nature of our magnetic
field, which acts as a vital shield against the harsh solar winds from the sun. Were it
not for our magnetic field - generated thanks the rate at which convection currents are
pushed through the outer core and mantle - then the sun would’ve stripped us of the life-supporting
air we breathe long, long ago! Taking the two closest planets to us, again; Venus doesn’t
have a magnetic field because there isn’t enough convection happening below the ground,
and Mars’s has as good as disappeared because its core also doesn’t generate the energy.
It’s another critical set-up where Earth has just the right balance.
The presence of liquid water is obviously another hugely significant fact of Earth - with
71% of our planet’s surface covered by water. Though the exact cause for this is up for
debate, it’s thought that water and ice first accumulated here via asteroid and meteor
impacts when Earth was young. Thanks, once again, to this particular world hosting the
right temperatures at the right times, the water was able to remain and, in time, the
oceans developed.
Scientists once assumed that planets in general had to be in the habitable zone to have any
chance of hosting water, but those ideas have now been thrown into major doubt following
the discoveries of potential lakes on the Jovian moon, Europa - as well as elsewhere
in the solar system. But what is known, and what further adds to the list of reasons why
Earth is “special”, is that it has just the right amount of water - not too much to
cover everything there is, but more than enough to avoid it turning into a dry and desperate
desert. Given that, though the debate on the origins of life rumbles on, many believe that
it started in water… there’s really no overexaggerating just how key water is to
our planet’s history.
Still, even with optimum temperatures, a reliable atmosphere and enough water, Earth might well
have ceased operations a long time before now. It’s ability to, in effect, recycle
itself is also very important. As far as we know, there’s no other planet or body in
our solar system that has tectonic plates. Mars and Venus don’t; Mercury and the moon
may have had them at one stage, but no longer; and the gas and ice giants, naturally, don’t
at all have the same composition as the terrestrial inner planets. The closest we get to a set-up
like our own is maybe, possibly on satellites like Jupiter’s moons Ganymede and, again,
Europa - where it’s thought that there are ice plates moving around and against eachother.
Aside from shifting continents, triggering earthquakes and forming volcanoes, plate tectonics
have also been central in shaping exactly what the Earth looks like - including where
the water is - while plate boundaries also act as recycling points of sorts, making sure
that there’s continuous change on the surface. In fact, thanks to tectonic movement, while
Earth is some 4.5 billion years old, the oldest parts of the seafloor are only around 200
million years old - once more helping to maintain rich and habitable conditions.
All of which leads us to Earth’s most special feature of all - life itself. And not only
simple, single-celled microbes but complex and intelligent beings! Life has had to survive
for billions of years, adapting all the while, to eventually develop into us; everything
that’s alive today. Life has seen off various deadly extinctions and survived long stretches
of major upheaval. Yet, it’s continuation is still wholly dependent on a long list of
variables staying exactly as they are… We’ll always need an atmosphere and water; we’ll
always need our planet’s core to generate a magnetic field and the convection currents
in the mantle to fuel change; and we’ll always require our life-enabling position
in this solar system’s habitable zone. Given how many things could’ve turned out differently,
it perhaps seems improbable that we’re even here at all. But that’s what’s so special
about planet Earth.
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