## Monday, February 6, 2012

### Slice of the Earth

Working up at 9,200 feet (2,800 meters) on Mauna Kea the other day I gained a new perspective on just what a thin shell humanity inhabits on this great giant globe of ours. At that elevation anything more strenuous that a walk becomes noticeably more exerting, due to the fact that you're working in about 70% of normal atmospheric pressure. This led me to ponder just how thin a volume people really live in, compared to the size of the Earth. As an astronomer I'm always interested in a new perspective, and being the visual sort of chap I am I decided to make something visual to explain.

I ended up creating the picture below, which attempts to show a slice though the Earth down to the core and compare it to a few other things, namely the heights of Mt. Everest and Mauna Kea and the depth of the Marianas trench. I decided to create it with a scale of one kilometer per pixel. Since the mean radius of the Earth is 6,371 kilometers, this is a BIG picture. It's so big I decided to just write my commentary in, rather than write a bunch more and have you scroll through a large boring picture. The reason I chose that scale is so that details at the surface could actually be made out, since the Earth turns out to be smoother than a pool ball if you compare them.

I also learned, upon trying to upload my finished masterpiece, that Blogger apparently has a maximum filesize limit (whether data-size or pixel-size I don't know, but frustrating either way). It cheerfully uploaded my picture without telling me anything was wrong, only for it to show up at about a quarter size, completely unreadable. I therefore remedied the problem by chopping my work into quarters (which hurt, artistically) which you see below. It's not quite as pretty as it is in its entirety (saving at lower quality to decrease the file size didn't help either), but I think it manages to get the idea across. Enjoy!

Edit (2/8/12): Today I went back, changed some of the text around, and split the picture into six pieces, each of which I saved as a PNG file, so the overall quality is much better. Check out the new and improved version below.

Final thoughts: this picture was a beast to put together. It took me the first five of Beethoven's symphonies plus I-don't-even-remember-how-many Vivaldi concerti. There are 4,122,000 pixels in the (original) picture, spread over 48 different layers (mostly because almost every bit of text automatically makes its own layer). It was tough, but I think the results are worth it.

Edit: Sometime after making this picture I learned that I'd drawn the Marianas Trench completely wrong. In actuality, it would look more like an inverted version of Mauna Kea—rather than a steep-sided canyon, it's more of a very gently-sloping depression in the ocean floor. The depth is still correct, but just imagine it being a very gentle depression sloping out at a very low angle.

1. WOW! Awesome Daniel. I am definitely going to circulate this! I cannot imagine how much work that must have taken.

2. Neat, although saving text in JPEG form makes it kinda lossy artifact-y and harder to read. What do you think of the theory that there's a big ball of Uranium in the middle?

3. Sharing with siblings; muchas gracias!

4. Nice! Now to find a host that will allow you to post the full, HD graphic!

5. Nice graphic! Yes, it is kind of crazy when you consider that only ~0.05% of the volume of the Earth is actually habitable by people.

6. Thank you everyone for your kind comments! I always enjoy it when something I make manages to strike a chord with people.

@Dan: Problem fixed now by splitting the image into more pieces and saving as PNG's. It was late when I finished the picture the first time, I was tired, and I wasn't sure if Blogger was having a problem with the data-size or the physical size of the pictures, so I played it safe and minimized both. I think you'll find it a bit easier on the eyes now.

As to the big ball of uranium, I haven't heard that theory, but here's what I know: there has to be something down there increasing the density above that of pure iron or nickel (you can only increase the density of a solid metal by pressure so much), and it's thought that there's a pretty good amount of both uranium and thorium in the core, but the measured density of the core is a whole lot lower than that of pure uranium, by about a third.

7. There are a lot of radioactive elements in the core (hence the radioactive decay responsible for geothermal), as well as elements such as nickel (which is thought to be abundant) that are heavier than iron. Kind of a head trip when you remember it all originally came from a supernova.

Think I said something interesting or insightful? Let me know what you thought! Or even just drop in and say "hi" once in a while - I always enjoy reading comments.