SPHERES

 You're about to hear more about spheres than you ever dreamed you would hear.  It won't hurt.  Learning something, for the most part, is harmless.

You are standing on Earth; within it's atmosphere.  Looking upward your eyes will see in order the troposphere (that's all around you and about 6 miles up), the stratosphere (airplanes can fly up there to about 30 miles up), the mesosphere (now we're into weather balloons and special planes from 30 miles to about 60 miles up), the thermosphere (watch out, there are satellites flying around here, it extends to 375 miles up), and the exosphere (here's where you'll see the space station or our distant satellites, it goes all the way to 6,200 miles up).  There is an ionosphere which overlaps several of these spheres and bounces radio waves back to Earth.  If you're wondering about the ozone layer, it's up there within the stratosphere. 

You may have heard of all that but you may not have heard about the spheres looking downward.  

The Earth is, on average, about 8,000 miles wide.  That's the mean diameter, give or take.  That tells us  that it is about 4,000 miles to the center of the Earth.  It's not just all mud.  We have some spheres involved there, too. 

You are standing on the crust.  More of the crust is under water but I assume you aren't standing on the ocean floor.  If you dig down a little ways, you'll be into the Mantle of the Earth.  The first 60 miles downward is know as the Lithosphere.  Dig past that for another 370 miles and you've been digging in the Asthenosphere.  Are your fingernails dirty yet?  Now, the next 1,430 miles down is called the Mesosphere part of the Mantle.  

If you've kept up with the math, you're down 1,800 miles right now.  You have reached the Core of the Earth.  The Core is made up of two parts, the Inner and Outer Core.  Remember, the whole distance to the center is about 4,000 miles.  The Outer core goes on for about 1,400 miles which puts you 3,200 miles below ground as we know it.  That leaves another 800 miles of Inner Core.

There will be a test on this next week.  I just love this stuff.