Everyday Science
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Everyday Science

Our Planet Is Like A Big Peach

And we are living on its peel

Photo by Sara Cervera on Unsplash

The shape of Earth

OK, hold on because I’m telling you two big secrets:

  1. Earth is not flat. It’s like a ball slightly squashed from the top. Technically its shape can be approximated as an oblate spheroid, but we can consider it a sphere.
  2. It is not hollow either. Jules Verne’s Journey to the Center of the Earth is a work of invention, there is no prehistoric world waiting for us deep inside Earth.
Earth from the Space | Photo by The New York Public Library on Unsplash

And if you are wondering how I can be so sure of these two facts, is because of two things: satellites and seismometers. The former can (among the other things they do) provide spectacular high resolution photos of our planet from the space; while the latter register seismic waves travelling across Earth, providing insights on its composition.

Mapping Earth using Earthquakes | Picture by SEWilco, Public domain, via Wikimedia Commons

Size matters

Now we all agree about the shape of Earth, let’s take a look at its size. Earth has a diameter measured at the equator of 12 756.2 kilometers, and of
12 713.6 kilometers if measured between poles, so its flattening is quite small, only 42.6 kilometers, making our planet almost indistinguishable from a sphere for most practical purposes.

I think we all agree that, compared to human scale, Earth is a quite big ball, even if it is not particularly remarkable in astronomical terms, except for the small detail it is the only known planet hosting life. In fact, it is eleven time smaller than Jupiter, the biggest guy in the planet crew.

Take a look inside

If you cut our planet in two, you would (other than completely destroy the life on it) find it looks quite like a giant peach.

Earth structure | Kelvinsong, CC BY-SA 3.0 via Wikimedia Commons

At the center, there is a big core, that is actually divided in two parts, like a peach stone: the inner core, solid, corresponding to the seed, and the outer core, corresponding to the endocarp. Inner and outer core together form a sphere which radius is 3 486 kilometers, around half of the whole Earth one. All the remaining part but a crust between 5 and 70 kilometers thin, is occupied by the mantle.

The crust thickness (we should write thinness) represent less then 1/100 of the Earth radius, even less than the peel-to-fruit ratio in a peach, but it is the only known place that hosts life. Almost all the living beings are confined between 10 984 meters below sea level (the Challenger Deep in Marianas Trench) and stratosphere lower limit, at 12 000 meters of altitude. Everything is happen here, in a 23 kilometers thick layer, less than 0.004 times the Earth Radius.

Where nobody has gone before

Photo by Norbert Kowalczyk on Unsplash

The highest continuously inhabited place is the International Space Station, orbiting at 400 kilometers, while the deepest point underground is the Kola Superdeep Borehole, a 30 centimeter-wide hole drilled down to 12 262 meters drilled in the Russian crust, 1/500 of the Earth radius. Not a spectacular result for a species claiming to rule the planet.

We, as humans, believe we have great powers, so great to destroy our planet, but the reality is we are nothing more than dust on the planet peel, not even able to reach what is below. The only thing we can do is make our home so inhospitable we will not able to live on it anymore.

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Diego Tonini

Diego Tonini

Writer and science communication enthusiast, I think science can be fun and everyone can understand it!