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What's So Special About Earth | Unveiled

VOICE OVER: Noah Baum WRITTEN BY: Dylan Musselman
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? In this video, Unveiled discovers exactly why Earth is like it is... and whether it's really so special at all?
Transcript

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?

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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