<p>It's all in how one chooses to define it M.Connor.</p>

<p>Often in physical science courses, we <a href="https://www.eartheclipse.com/geography/4-different-spheres-of-earth.html" rel="noreferrer">define the Earth system</a> as the lithosphere (rocks), atmosphere (air), biosphere (life), and hydrosphere (water) [also sometimes separately defining a 5th aspect, the cryosphere, which is ice]</p>

<p>In the end, we often just think of the Earth as everything confined by its gravity (not including in orbit) as that's everything still controlled by the Earth.</p>

<p>But in a very true sense, you're still leaving the Earth when you take off on a plane.<br>
Just you're still in a state/region of the Earth's system where what goes up must come down.  So you won't be gone long!</p>

CC BY-SA 3.0
2018-04-13T12:29:37.453Z
2018-04-13T12:29:37.453Z
JeopardyTempest
<p>Yes, the atmosphere is part of the Earth and as others here have stated the atmosphere thins (decreases in density) with height.</p>

<p>The aviation and outer space communities use the <a href="https://en.wikipedia.org/wiki/K%C3%A1rm%C3%A1n_line" rel="nofollow noreferrer">Karman Line</a> as the boundary between the Earth's atmosphere and outer space. This line is 100 km above sea level. </p>

CC BY-SA 3.0
2018-04-14T12:12:31.177Z
2018-04-14T12:12:31.177Z
Fred
<p>My question is quite simple, but I can't seem to find any answer to it: how do we define the limit of the object "Earth"? More specifically, can we consider the atmosphere a part of it? Or even the oceans, for that matter? I was going for a no at first glance, but that would mean that you are actually leaving the Earth when you fly on a plane. That feels weird. How do scientists define the limit of the Earth?</p>

CC BY-SA 3.0
2018-04-13T13:02:35.853Z
The density of the atmosphere gradually gets smaller as we move away from earth. To draw a line anywhere will anyways be artificial. In earth sciences earth is divided to spheres (like hydrosphere, atmosphere) and the outermost layer that is named (and thus can be thought as an attribute of earth) is exosphere and its upper limit isn't defined other than: where objects are still bound to earth's gravitation.
Communisty
<terminology><planetology>
Is the atmosphere a part of Earth?
M.Connor
# Is the atmosphere a part of Earth?

(Asked by: username_0 on 2018-04-13)

My question is quite simple, but I can't seem to find any answer to it: how do we define the limit of the object "Earth"? More specifically, can we consider the atmosphere a part of it? Or even the oceans, for that matter? I was going for a no at first glance, but that would mean that you are actually leaving the Earth when you fly on a plane. That feels weird. How do scientists define the limit of the Earth?

**Tags:** terminology, planetology

> **Comments:**
> **username_1**: The density of the atmosphere gradually gets smaller as we move away from earth. To draw a line anywhere will anyways be artificial. In earth sciences earth is divided to spheres (like hydrosphere, atmosphere) and the outermost layer that is named (and thus can be thought as an attribute of earth) is exosphere and its upper limit isn't defined other than: where objects are still bound to earth's gravitation.  

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## 2 answers

### Answer by username_2 on 2018-04-13. Score: 5 | Accepted answer

It's all in how one chooses to define it username_0.

Often in physical science courses, we [define the Earth system](https://www.eartheclipse.com/geography/4-different-spheres-of-earth.html) as the lithosphere (rocks), atmosphere (air), biosphere (life), and hydrosphere (water) [also sometimes separately defining a 5th aspect, the cryosphere, which is ice]

In the end, we often just think of the Earth as everything confined by its gravity (not including in orbit) as that's everything still controlled by the Earth.

But in a very true sense, you're still leaving the Earth when you take off on a plane.  
Just you're still in a state/region of the Earth's system where what goes up must come down. So you won't be gone long!


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### Answer by username_3 on 2018-04-14. Score: 2

Yes, the atmosphere is part of the Earth and as others here have stated the atmosphere thins (decreases in density) with height.

The aviation and outer space communities use the [Karman Line](https://en.wikipedia.org/wiki/K%C3%A1rm%C3%A1n_line) as the boundary between the Earth's atmosphere and outer space. This line is 100 km above sea level.


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