Greenhouse effect: why is carbon dioxide trapped in the atmosphere?

Question

I know that the greenhouse effect is caused mainly because carbon dioxide gets trapped in the atmosphere, and the sun's heat cannot escape the earth. But why does the carbon dioxide get trapped in the atmosphere? Is it the earth's gravity holding it down?

Answer 1

Comparatively, the earth's atmosphere is thinner than the skin of an apple.
The atmosphere is held by gravity. This is why small planets and moons don't have atmospheres.
The earth's magnetic field also plays a role in protecting the atmosphere from being blown away by the energy forced out of the sun. The atmosphere of Mars was probably much thicker than it is now, but it has been pushed away by solar wind.
Without that small amount of carbon dioxide in our atmosphere, the average temperature would be about -15°C instead of 15°C.

Answer 2

yes - that's exaclty it. The atmosphere is held in place by Earth's gravity. What is happening with "the greenhouse effect" is that carbon from fossil fuels (prevously buried underground for hundreds of millions of years) is being released into the atmosphere and changing its composition.

Answer 3

It isn't trapped there. There is a complete carbon cycle, where most of the CO2 is consumed by green algae in the worlds Oceans and eventually becomes limstone and goes back into the mantel at the edges of continents and is spewed back out in volcanic eruptions. In fact one large volcanic eruption produces more CO2 than humans have produced by burning fossil fuels and wood since the begining of time.

Answer 4

You got it. That is why very light gases can escape into space . . .