According to the GRC NASA website, Earth's atmosphere is a thin sheet of air extending from the surface of the Earth to the edge of space. Some videos on youtube also point out that if the Earth is the size of an apple, its atmosphere is just as thick as the apple's skin. But when we look at some diagrams, Earth's atmosphere is thick. For instance, when someone says that the atmosphere is a thin sheet of air, does he/she take in to account the thick layer thermosphere or exosphere? Or is it just that the diagrams we commonly see have inaccurate visual representation?
The answer to your question depends on where one defines the edge of the atmosphere.
The Earth's atmosphere is layered. The thickness, density of composition of each layer varies. The five layers are:
- Exosphere: 700 to 10,000 km (440 to 6,200 miles)
- Thermosphere: 80 to 700 km (50 to 440 miles)
- Mesosphere: 50 to 80 km (31 to 50 miles)
- Stratosphere: 12 to 50 km (7 to 31 miles)
- Troposphere: 0 to 12 km (0 to 7 miles)
Being the outermost layer, the exosphere is the layer with the most nebulous upper boundary. It is also the layer with the lowest density and it is primarily composed of very low density hydrogen and helium, particularly in the outer/upper reaches.
Because of the low density of the exosphere and also because the Karman Line, which is 100 km above the Earth, which the line designated where Earth ends and outer space begins, the exosphere is sometimes ignored.
So if one accepts the top of the Thermosphere as being the effective upper boundary of the atmosphere the effective thickness of the atmosphere is only 700 km compared the radius of the Earth, which is 6370 km.
But when we look at some diagrams, Earth's atmosphere is thick. For instance, when someone says that the atmosphere is a thin sheet of air, does he/she take in to account the thick layer thermosphere or exosphere? Or is it just that the diagrams we commonly see have inaccurate visual representation?
You are probably referring to diagrams such as this one, dramatically not to scale, yet from a reputable source (the European Space Agency):
The only reason these diagrams are not to scale is the sake of readability. They could never fit those fancy planes, balloons and satellites if the diagram was at scale. I've tried: I traced this diagram with Inkscape, using Fred's answer numbers and a 1:100,000,000 scale (on my diagram the Earth has a 6.37 cm radius). I purposely forgot the troposphere line so we could see better. So, from the centre outwards, you have:
- Earth's surface.
- A thick line which represents the top of both the stratosphere and the mesosphere (at 1 pt thickness they are too close to be able to distinguish them).
- The top of the thermosphere. If you consider this to be the limit then yes, the Earth is like a thick-skinned fruit (grapefruit maybe?).
- The top of the exosphere.
It would be pretty hard to squeeze a fancy plane in there, or even a caption to label the layers!
The referenced website claims that "The Earth's atmosphere is an extremely thin sheet of air extending from the surface of the Earth to the edge of space. If the Earth were the size of a basketball, a tightly held pillowcase would represent the thickness of the atmosphere."
The website apparently is using the altitude at which the US awards someone Astronaut Wings as "the edge of space" -- 50 miles, or about 80 kilometers. Shrinking the Earth to the size of a basketball would shrink 80 kilometers to 1.5 millimeters, which is about the thickness of a pillowcase. Things can orbit the Earth and have orbited the Earth at 85 kilometers altitude (for a few orbits). Since about 99.998% of the mass of the atmosphere is at an altitude of 85 kilometers or less, that usage is not unreasonable.
The remaining 0.002% of the atmosphere's mass gets thinner and thinner with increasing altitude, but the atmosphere arguably continues to at least half of the way to the Moon. In that sense, claiming that the Earth has a thin atmosphere is incorrect. But that is a thin claim (pun intended).
Depends what you're interested in, but if you take the atmosphere as being the breathable atmosphere its only about 6km thick.
This is important because when people think about air pollution if you have a visual in your mind that the pollutants we put into the air all being concentrated into that thin layer then you start to think differently. So if the earth was a basketball, the breathable atmosphere on which we depend is about a tenth of a millimetre thick.