Earth
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Earth

Here we are with our eyes and our minds and our curiosity, six [now seven] billion passengers aboard a tiny blue boat, bobbing and wheeling our way around one vast Catherine wheel among many.

At the first glance of an alien observer, the Earth may appear to be a small, ordinary rock orbiting an average and unremarkable star.

It has a thin layer of gasses enveloping the planet (our ‘atmosphere’) which is good to have, but isn’t particularly remarkable.

The exact chemical makeup of the planet is certainly unique, but in the same way that any random assortment of letters is unique.

//They might notice atmospheric oxygen, a sign of life…

//What makes the planet interesting is how they’re put together.

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But the Earth enjoys a number of unlikely characteristics that sets it apart from other planets.

One of the most fundamental reasons is something that’s quite simple: It’s easy for materials to get mixed together.

Like most planets the Earth is unevenly heated by the Sun, being hotter at its equator and cooler at its poles. But it also spins (creating day and night), and wobbles (creating seasons).

It’s lucky for us that our planet is about half-full of water, which at it turns out is not too much and not too little.

Because of its distance to the Sun and composition of its atmosphere, it has a range of temperatures where water is constantly cycling between states (I.e. between being a gas, liquid, and a solid).

This brings our planet alive.

Water is an excellent solvent, so in its liquid state it carries many interesting dissolved and mixed up materials around and then releases them in other places, acting as a kind of giant ladle that mixes up the soup of Earthly materials.

Carbon, nitrogen, hydrogen, and oxygen, the four central elements to biochemistry, constantly cycle across the Earth in different forms, and often in chemical configurations that make it possibly for life to utilise them.

A relatively short period of time after its formation, the chemical soup of the Earth created by chance a unique type of molecule. It could create rudimentary copies of itself, by attracting component parts and catalysing their reaction to form a similar molecule.

This molecule was the first piece of RNA and the first known instance of life, which went on to built elaborate structures around itself. First it built a cell with structures like walls and organs like the mitochondria, and learned to use sunlight and the energy and materials of other cells.

Second, the interaction of these cells with each other and their environment created the first ecosystems.

Third, some cells began to cooperate to create extremely elaborate multi cellular organisms, building eyes, brains, muscles, and other organs made of cells. This created the first invertebrates, fish, amphibians, reptiles, birds, and eventually mammals including humans.

Very recently, the human multicellular animal created a whole new type of organisation - a civilisation, based on collective knowledge and cooperation.

But we still carry a highly developed version of RNA in every cell of our bodies, a humble reminder of what we fundamentally are.

The attributes of the Earth led to the development of life. As life diversified and grew, it worked its way into every habitable nook and cranny of the Earth, until the biosphere itself became inseparable from the cycles of carbon, nitrogen, hydrogen, and oxygen that made it.

David Attenborough, The Living Planet

Our planet, the Earth, is, as far as we know, unique in the universe. It contains life. Even in its most barren stretches, there are animals. Around the equator, where those two essentials for life, sunshine and moisture, are most abundant, great forests grow. And here plants and animals proliferate in such numbers that we still have not even named all the different species. Here, animals and plants, insects and birds, mammals and man live together in intimate and complex communities, each dependent on one another. Two thirds of the surface of this unique planet are covered by water, and it was here indeed that life began. From the oceans, it has spread even to the summits of the highest mountains as animals and plants have responded to the changing face of the Earth.

Earth has an number of other attributes that may have contributed to its unique situation.

It is protected from asteroids by Jupiter, which unintentionally acts as a giant, space based shield.

It has a balance of dynamism that comes from its size. It is large enough to create gravitational pressure to break down the rocks of the crust and cycle them in convection currents. But it isn’t so strong that it prevents a crust from forming altogether. This cycles the materials of the planet and imbues them with geothermal energy.

Great oceans modulate temperature, by acting as a heat sink that moderates extreme spikes of temperature.

The Earth has an oversized moon (being the largest moon relative to the size of its planet in the solar system). It creates strong cyclical tides, further contributing to the mixing up of materials on Earth. This may be incredibly important, as cycles of hydration and dehydration can create elaborate chemical molecules.

The moon is also incredibly poetic, as by sheer cosmic coincidence the moon appears to the same size as the Sun in our sky. This may be unique among all the planets of our galaxy.

…An interesting question that I do not know the answer to is; Is there is a cycle for every naturally occurring material on Earth - and I suppose nowadays for man-made ones too? They may differ in time scales by tens of millions of years, but surely all materials from the crust of the Earth upwards into the atmosphere have some kind of cycle?

We do not have enough information to know whether or not these things are necessary in the formation of life, as our sample size for planets with life remains at one. These aspects make it all the more difficult to build theories around what is important when it comes to the formation of life.

Beauty

No place will ever look as beautiful to a species as its home world. Our eyes are evolved to the textures, colours, and light conditions of our home. No other planet will be able to appear to be as rich and textured to us as this one.

Our eyes evolved to see the green of the plants that blanket the Earth in contrast to the blues of the sky, and flavours of red that stand out vibrantly against the green backdrop of a forest.

A life form that evolved on Mars might see a starker difference between its red sand and its yellow skies - perhaps as highly contrasting colours that we're familiar with, or perhaps as completely different colours than what we use.

We could scarcely hope to find and explore a world as vibrant and as full of life as the Earth. If you are searching the void of space and thousands of scorched worlds for exotic life forms, advanced alien cultures and technologies, you would do well to discover the mirror.

Scuba diving is a great place to start.

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Brian Swimme and Thomas Berry, The Universe Story

After long centuries of inquiry, we find that the universe developed over fifteen billion years, and that the eye that searches the Milky Way galaxy is itself an eye shaped by the Milky Way. The mind that searches for contact with the Milky Way is the very mind of the Milky Way galaxy in search of its inner depths.

Phenemonea

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Solar eclipses

Sunsets

Sunrise and sunset is a band that moves across the earth. It doesn't disappear when it dips below the horizon, it just moves west.

Someone's midday is someone else's sunset. The same orb is in the sky.

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Rivers

Henry David Thoreau, journal entry for Spring, 1838

For the first time it occurred to me this afternoon what a piece of wonder a river is...a huge volume of matter ceaselessly rolling through the fields & meadows of this substantial earth.

Oceans

I find the beauty of a shoreline lies with the ocean. It's vastness. It's infinite surface shape. It's infinitely changing liquid form.

It is complimented by the rough, solid, unchanging cliff face along the shoreline, as gold lace runs along an emperor's purple robes.

Canyons

Canyons with rivers down the bottom tell you just how long that river has been eroding the area.

These rivers carve a valley one grain of sand at a time.

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Weather

From <https://www.reddit.com/r/explainlikeimfive/comments/b1c6z6/eli5_if_clouds_are_just_water_vapour_why_can_we/>

Clouds aren't water vapor (gas), they're made of liquid water droplets and frozen crystals, just like fog.

Rain from another perspective. Watch the gif here.

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Clouds

Clouds with flat bottoms are rising water balloons.

There are invisible bubbles of water vapour rising through the air.

They become visible when the water has dropped enough for them to cool into droplets.

This happens at a very specific point, and is why many clouds have a 'flat' bottom.

The water vapour bubble should continue to rise, and the cloud should keep growing.

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Tornadoes

They are just the result of air coming in to a spot from all lateral directions, that has nowhere else to go but upwards.

Click here to watch this gif of a model simulation of a tornado.

Composition

Each planet and moon has different levels of chemicals and elements in their makeup. In addition to their history and location, these compositions make them unique.

This is the unique makeup of the Earth:

Water

Earth actually doesn't have a relatively large amount of water

From <https://aeon.co/essays/in-a-galaxy-awash-in-water-do-any-other-worlds-have-just-enough>

From our parochial perspective, Earth seems to be the quintessential ocean planet – the Pale Blue Dot – dominated by its seas. But all those oceans amount to the thinnest of films on the planet’s surface. By mass, Earth is only .025 per cent water. With current technology, astronomers would be unable to tell if an exoplanet such as Earth had any water at all. Astronomers use two basic techniques to determine the compositions of exoplanets. First, they estimate a planet’s size by observing how much light it blocks as it passes in front of its star. Then they measure the ever-so-slight wobble imparted to the star by the orbiting planet, which yields the planet’s mass. Dividing the planet’s mass by its volume gets the density, which in turn gives astronomers a rough idea of the percentages of gas, rocky matter and water in the planet.

‘Think about how thin our ocean is,’ says Desch. ‘It doesn’t change Earth’s radius in any way.’ For now, he says, astronomers can tell if an exoplanet has oceans only if water accounts for about 10 per cent of its mass. And that, as mentioned above, would equal 400 Earth oceans, a life-crushing amount of water. So the only water worlds we can detect with existing technology would be unlikely to host any life. ‘That’s state of the art right now,’ says Desch. ‘We have the ability to look for water and we can see it when there is 10 per cent water, but that is *way* too much water.’

Geology

Elevation and continental shift

There is much more to the topography of the Earth than what you see on a typical map.

We just see the tips of the huge structures of the Earth that are above the water, but most of them are under the ocean.

This image lets you see that there is a lot going on below the ocean. You can see that land masses are just the tops of these massive shapes in the Earth's crust.

Because the crust is shifting, they move like waves along the surface.

See if you can get a video of the elevation of all the continents, changing over time.

Over time these:

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This is a video of how these continental land masses have changed throughout the history of the Earth. Note that a lot of tedious work has gone into working this out, mostly by comparing thousands upon thousands of rocks.

If you were to take a cross section of the Earth's crust, it would look something like this.

Cross-section

Changing shorelines

In the larger scheme of things, shorelines change all the time (i.e. every few thousand years).

Look at Europe as an example.

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How are new rock layers formed?

How are new rock layers formed in the earth? Are they *all* from volcanic activity?

This is a question that I want to find an answer for.

Beneath the crust

"Everything we know about the mantle, which begins about 15 miles below the surface, and about Earth’s core, 1,800 miles beneath us, has been gleaned remotely."

Others have mentioned the Kola dig, which is also discussed in the article.

Tim Folger, Journeys to the Center of the Earth

"Temperatures at the bottom of the Kola hole exceeded 300 degrees Fahrenheit; the rocks were so plastic that the hole started to close whenever the drill was withdrawn . . . And the depth of the Kola hole after 24 years of drilling? About 7.6 miles — deeper than an inverted Mount Everest and roughly halfway to the mantle, but still a minuscule distance, considering Earth’s 7,918-mile diameter. If Earth were the size of an apple, the Kola hole wouldn’t even break through the skin.

Space is closer than you think

The atmosphere is actually incredibly thin.

Sir Fred Hoyle

Space isn’t remote at all. It's only an hour's drive away if your car could go straight upwards.

Carl Sagan, quoted in An Inconvenient Truth

If you had a globe covered with a coat of varnish, the thickness of that varnish would be about the same as the thickness of the Earth's atmosphere compared to the Earth itself.

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A new perspective

  • In the old mythologies of many cultures, gods dwelt on the tops of mountains where they had a commanding perspective of the world below. Climbing a mountain was often a sacred experience, and an important part of that experience was the literal new perspective that it would give.
  • Although had already discovered millennia or centuries ago that the world is round, that the Earth is an interconnected system, and that it inhabits a great void dwarfed by other planetary bodies, human beings never got to experience this in a truly visceral way. Climbing a mountain would let us see the wrinkles and ridges in the Earth, like it were a great pea, and the variety of life and human industry that sometimes stretched across it.
  • But at no point could we rise above the gravity well that Earth creates to get a sense of the whole picture. We were stuck, like a creature at the bottom of a well trying to understand the glimmer of a world far above us.
  • That was until about 70 years ago, when we repurposed a rocket originally designed to destroy cities, and sent it to space with a camera.
  • This was the first image of the Earth from space that we ever took, by a repurposed Nazi-built V2 rocket on Oct. 24, 1946.
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  • The first image of Earth from space
  • The grainy, black-and-white photos were taken from an altitude of 65 miles by a 35-millimeter motion picture camera riding on a V-2 missile launched from the White Sands Missile Range. Snapping a new frame every second and a half, the rocket-borne camera climbed straight up, then fell back to Earth minutes later, slamming into the ground at 500 feet per second. The camera itself was smashed, but the film, protected in a steel cassette, was unharmed.
  • Fred Rulli was a 19-year-old enlisted man assigned to the recovery team that drove into the desert to retrieve film from those early V-2 shots. When the scientists found the cassette in good shape, he recalls, "They were ecstatic, they were jumping up and down like kids." Later, back at the launch site, "when they first projected [the photos] onto the screen, the scientists just went nuts."
  • Tony Reichhardt, First Photo From Space
  • This opened the door for truly, viscerally seeing the Earth that we live on for what it truly is. One photo followed another, increasing in available colour and resolution.
  • This photo was from Lunar Orbiter I, one of the first spacecraft (this one was unmanned) to orbit the moon, in 1966.
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  • Earth from Lunar Orbiter I
  • This was followed by a photo taken by Apollo 8 in 1968, called 'Earthrise', later reproduced in video by Apollo 10.
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  • Earthrise, from Apollo 8
  • Afterwards came a photo taken by Apollo 17, called the 'Blue Marble', one of the reproduced images in human history.
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  • The blue marble, from Apollo 17.
  • Until we had the chef d'oeuvre, the 'Pale Blue Dot', taken by Voyager I in 1990.
  • Seen from about 6 billion kilometers, Earth appears as a tiny dot (the blueish-white speck approximately halfway down the brown band to the right) within the darkness of deep space.
  • Wikipedia, Pale Blue Dot
  • Accompanying this image is a quote by astronomer Carl Sagan:
  • We succeeded in taking that picture, and, if you look at it, you see a dot. That's here. That's home. That's us. On it, everyone you ever heard of, every human being who ever lived, lived out their lives. The aggregate of all our joys and sufferings, thousands of confident religions, ideologies and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilizations, every king and peasant, every young couple in love, every hopeful child, every mother and father, every inventor and explorer, every teacher of morals, every corrupt politician, every superstar, every supreme leader, every saint and sinner in the history of our species, lived there – on a mote of dust, suspended in a sunbeam.
  • The Earth is a very small stage in a vast cosmic arena. Think of the rivers of blood spilled by all those generals and emperors so that in glory and in triumph they could become the momentary masters of a fraction of a dot. Think of the endless cruelties visited by the inhabitants of one corner of the dot on scarcely distinguishable inhabitants of some other corner of the dot. How frequent their misunderstandings, how eager they are to kill one another, how fervent their hatreds. Our posturings, our imagined self-importance, the delusion that we have some privileged position in the universe, are challenged by this point of pale light.
  • [...] To my mind, there is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world. To me, it underscores our responsibility to deal more kindly and compassionately with one another and to preserve and cherish that pale blue dot, the only home we've ever known.
  • Carl Sagan, Lecture at Cornell University 1994
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  • The pale blue dot
  • Here are an assortment of images from astronauts in orbit.
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That's the south island of New Zealand and the north island in the top corner, I think.

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Finally, the Earth as seen from other planetary bodies in an infographic.

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Satellites

The fact that we've managed to put satellites in space is something that would be inconceivable to every human being in our collective history beyond the current era.

The International Space Station

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How much gravity is there?

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Space debris

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The Moon

The Earth and moon exist as a single system. The relationship between the two is unique, at least for as far into the universe as we can see.

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  • The moon has to be one of the most poetic beings in the universe. It appears as the perfect opposite to the sun - almost the exact same size in the sky, and tidally locked to appear for us every night. It lends itself so well to poetry, art, and mythology, with the pair forming a perfect god/goddess duality of night and day.
  • When the sun is shining on the surface at a very shallow angle, the craters cast long shadows and the Moon's surface seems very inhospitable, forbidding almost. I did not sense any great invitation on the part of the Moon for us to come into its domain. I sensed more almost a hostile place, a scary place.
  • Michael Collins, Command Module Pilot for Apollo 11, quoted in In the Shadow of the Moon (2007)
  • The Moon was the most spectacularly beautiful desert you can ever imagine. Unspoiled, untouched. It had a vibrancy about it. And the contrast between the Moon and the black sky was so vivid and... it just made this impression, you know, of excitement and wonder.
  • Charlie Duke, Lunar Module Pilot for Apollo 16, quoted in In the Shadow of the Moon (2007)
  • kyle90 248 points 1 year ago
  • What honestly interests me is how close they are. On an astronomical scale, the Moon is practically touching us. Also it's huge compared to the moons of other planets (when considered as a percentage of the parent body's mass).
  • We're lucky to have such an awesome object so nearby. I'd quite like to visit it someday.
  • content404 99 points 1 year ago*
  • I don't remember where I got this information/conclusions but the Earth and the Moon would more accurately be called the Earth-Moon System. The Moon is astoundingly close to Earth, from a cosmological perspective, and their relative sizes are also very close. Consider Mars and its moons, Phobos and Deimos[1] are basically asteroids[2] and most other moons in the solar system are completely dwarfed by their planets.
  • We owe a great deal to our moon. Life on this planet would be very different, if it managed to survive at all, without The Moon. Ocean tides 'stir' the waters of the planet, creating a semi-aqueous zone around every ocean which would be the perfect place for sea life to try to come up on land. The Moon also brightens the night sky, have you ever been out at night, in the wilderness, on a new moon? Most importantly for us though, it serves as an asteroid catcher, instead of a single gravity well around our planet there are two of comparable size[3] .
  • Earth is a Goldilocks planet for many reasons but an important one is often left uncited, our moon. When I see The Moon at night, I can't help but think about how critical it has been in our development. If Earth is our mother, then The Moon is undoubtedly our father.
  • He protected Earth while she was pregnant with early life. There are dangerous objects flying around our solar system and He took a beating so that She wouldn't have to. He has countless visible scars but still keeps constant vigil over his children. He helped raise us, holding our hands as we learned to walk and lighting up the nights so that we could see. And just like mother Earth, he has been a wonderful teacher. He taught us how to keep time which let us track the seasons. He helped us figure out how our solar system worked. He helped us learn about gravity. He showed us that relativity was correct, for the most part, and let us feel good about ourselves when we finally managed to say hi in person.
  • Finally, He'll give us a push as we leave home to join the real world, but only when we grow the fuck up and stop killing our brothers and sisters.
  • tl;dr I love The Moon, and you should too
  • Reddit community, The actual distance between earth & moon!
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Jupiter's protection

Jupiter may have played a large role in the formation and stability of the Earth than what it may initially seem.

It may have played a role in stabilising the Earth' orbit around the sun, reducing eccentricity and thus bringing some stability to Earth's climate.

It may have pulled the asteroids of the inner solar system towards itself and locked them into a stable orbit, thereby protecting the inner planets from greater bombardment.

It may actively protect the inner planets from asteroids from beyond Jupiter, by pulling them into itself.

The presence of a nearby gas giant therefore may be an important requirement for alien life to form on a planet. We call such a planet a 'good Jupiter'.

The future of the Earth

Life exists in a temporary window of opportunity on Earth, which will not last forever.

1 billion years from now

In about one billion years, the solar luminosity will be 10% higher than at present. This will cause the atmosphere to become a "moist greenhouse", resulting in a runaway evaporation of the oceans. As a likely consequence, plate tectonics will come to an end, and with them the entire carbon cycle.

4 billion years from now

During the next four billion years, the luminosity of the Sun will steadily increase, resulting in a rise in the solar radiation reaching the Earth. This will result in a higher rate of weathering of silicate minerals, which will cause a decrease in the level of carbon dioxide in the atmosphere. In about 600 million years from now, the level of CO2 will fall below the level needed to sustain C3 carbon fixation photosynthesis used by trees. Some plants use the C4 carbon fixation method, allowing them to persist at CO2 concentrations as low as 10 parts per million. However, the long-term trend is for plant life to die off altogether. The extinction of plants will be the demise of almost all animal life, since plants are the base of the food chain on Earth.

5 - 7.5 billion years from now

The Sun will swell into a red giant, engulfing Mercury and Venus and scorching the Earth, before engulfing the Earth too, in about 7.5 billion years from now.

That is where our atoms will all end up.

For context, the Earth is currently 4 billion years old.

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We sit on a solid surface below an ocean of gas
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Say hey to Owlbert Einstein

Curator of the Big Ideas Network

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