Have you ever wondered about mountains? Part one: the earth’s layers.

I’m guilty of it too. I walk around the world expecting it to serve me. It’s rare that I think about the people or things who have  gone around creating the world we live in. For this edition of “Have you ever wondered?” I started off wanting to know about mountains. Initially, I was bombarded by educational resources created for middle and high school students. I found almost nothing geared toward the average adult. Even the National Geographic site linked to educational resources for “more information.” I thought, “What gives?”

I am fairly confident that most adults are not experts in plate tectonics or volcanic eruptions–I can’t be the only adult who didn’t pay attention to and/or did not retain the information provided in earth science. When I asked Kyle what he knew about mountains he shouted  “…when the plates move!” Okay, yea, got it, but I want to know more. How quickly can a mountain form? When did the mountains form? Someone told me once that the Appalachian mountains used to be the tallest mountain range in world (55+ million years ago). Whaaaat??? How do they know that? I just. want. to understand.

What exactly makes a mountain……?

It’s clear to me that I’m going to have to start smaller. Unless I want to write 20 pages summarizing the intricacies of plate tectonics and volcanic activity and erosion and mass wasting, I’m going to have to either gloss over the topics, or split them up. I hope you don’t mind, but we’re going to start from the beginning.

The Earth’s Layers

We live on the top of a planet (197 million square miles of space) and beneath our feet is more than 7,900 miles of….”stuff.” Do you know what the “stuff” is? I don’t.

There are 4 layers that have been assigned by scientists: the crust, the mantle, the outer core and the inner core. 


These are the designations that are assigned based on the chemical components that make up the earth (meaning, what its made out of). Scientists also assign designations to layers of the earth based on its mechanical properties (whether it is liquid or solid). Those designations are the lithosphere, asthenosphere, mesospheric mantle, outer core and inner core.

Basically, it’s complicated.

Credit: pubs.usgs.gov

Scientists only know about what makes up the earth because of seismic discoveries. When there is an earthquake, the seismic waves travel through the layers of the earth. Each layer has different characteristics which are represented by changes in waves. Nobody’s traveling around in the earth’s mantel or core, so there’s a lot that we still don’t know. Before scientists started studying seismic waves, our ancestors thought that vicious animals lived below the earths surface and when they got angry, we experienced earth quakes. Aristotle changed the conversation when he predicted that wind storms within the earth were occasionally shaking what we now consider the earth’s crust. Here’s a little bit about what we do know:


The inner core is solid and is made up of iron and nickel which are heavy compounds. The temperature in the inner core is ~9,800°F. Iron and nickel’s melting points are 2,800° F and 2,651° F respectively, but high levels of pressure keep the compounds from liquefying. 

The outer core is also made up of iron and nickel, but it exists in a liquid state because the pressure is significantly lower than the inner core. The temperature ranges between 7,280°F and 10,340°F.

The mantle makes up 84% of the earth. Some parts of the mantle are solid while other are plastic and movable. The movement of tectonic plates is caused by the plasticity of the material found within the mantle. The “material” is made up of silicon, iron, magnesium, aluminum, oxygen and other minerals. Temperatures in the mantle can be as high as 4000°F and as low as 930°F.

The crust is outer most layer of the earth and since it’s the easiest to access, we know the most about it. I was surprised to learn that it only makes up 1% of the entire earth and can be at thin as 3 miles. The crust is made mostly of oxygen, aluminum, silicon, aluminum, calcium, iron, sodium, magnesium and potassium.

There are two types of crust: oceanic and continental. Pretty obviously, the oceanic crust lies beneath the ocean and is much thinner than the continental crust that is not covered by water. The base of the earth’s crust combines with the upper most region of the mantle to form tectonic plates (that’s the lithosphere). These tectonic plates sort of “float” on the regions of the mantle that are plastic. The “plasticity” of the mantle causes the plates to move a few inches per year.

Dun. Dun. Dun! This brings us to the study of tectonic plates! And that will help us to understand the formation and degradation of mountain ranges! Those are the things we love to explore! I get that this is probably boring for most people, but I’m just so excited.

When you stop to think about it, we, as humans, are just miniature being specs on top of this titanic object called earth.

Boom. Perspective.

The human condition has us worried about our outfits and what Suzie said about our new kitchen and who we’ll invite over for Thanksgiving dinner, but for me at least, studying a tiny bit about what happens 2000 miles beneath the earth’s surface makes my current concerns seem pretty insignificant.

I think that’s why we love to immerse ourselves in the wilderness. When you’re out there you can’t possibly be in here. Getting out there is an act of acknowledging that there are other things to consider besides what humans have created and agreed upon.

We hope you enjoyed the first installment of “Have you ever wondered about mountains?”

Until next time friends,

Sincerely yours,

The Mitteneers


  1. Mountains” from National Geographic Science
  2. Plate Tectonics” from National Geographic Science
  3. What is Plate Tectonics” from Live Science
  4. How big is Earth?” from Space.com
  5. Seismology from USCB

Leave a Reply