Thread: what if the Earth's atmosphere were thinner?

Hi all . As said in my intro, I'm here to ask a few questions (not for homework) that I was unable to find answers for in the Great Googleverse, neither did I wish to ask them in Yahoo Questions. Even though science (especially astronomy and cosmology) interests me, I've never had the chance to properly study it myself, save the programs on Discovery Science lol, so for all accounts and purposes I'm a layperson. These questions may sound ridiculously silly and newbie-ish but I hope someone has the patience and good nature to take the time to answer them.
(I love my disclaimer! I cannot bear to let it go!! )

My question this time is a hypothetical secanrio concerning the Earth's atmosphere:

1. Imagine the atmosphere thinned milennia ago. What could have caused this to happen, and how? (I'm guessing something to do with the magnetosphere and gravity?)
2. If it were any thinner (how much thinner I do not know), could it sustain life? What sort of life?
3. What would happen to the Earth under a thinner atmosphere?

Again, thanks for your patience and help.

Question 1 - any answer would be a wild guess.
Question 2 - it is quantitative. Slightly thinner - wouldn't make much difference. As thin as on Mars - completely different story.
Question 3 - I presume you are asking about the planet itself, not the life on it. It wouldn't make much difference.

Hi Mathman, thanks for the response.
Anyone else? Help a newb (and a lay newb at that) out?

I guess what throws us is you're calling it Earth. Planets loose their atmosphere but several means. Thermal escape, which is difficult except for hydrogen and helium for earth-mass planets. A period of major solar eruptions could do it because they assist molecules to escape velocity. A major impact can toss much of the atmosphere. Lastly gasses get sequestered into the lithosphere or hydrosphere--H2 combining with O2 to make water, Co2 becoming the carbonates beneath of feet etc.

I assume you're still working on your ideas for a fiction novel?

Originally Posted by Lynx_Fox

I guess what throws us is you're calling it Earth. Planets loose their atmosphere but several means. Thermal escape, which is difficult except for hydrogen and helium for earth-mass planets. A period of major solar eruptions could do it because they assist molecules to escape velocity. A major impact can toss much of the atmosphere. Lastly gasses get sequestered into the lithosphere or hydrosphere--H2 combining with O2 to make water, Co2 becoming the carbonates beneath of feet etc.

I assume you're still working on your ideas for a fiction novel?

Thanks for the reply, even though much of it escapes me lol.
And yes I am.

One of the problems for a book is most of the things that would rip off a good fraction of the atmosphere would devastate the surface life.
For example:

A huge asteroid impact-- probably kills everything on the surface.

Less physically destructive might be say severe solar storms during a time when our magnetosphere is very weak, such as during one of the periodic polarity shifts. But that too would probably fry much of the surface life.

The sequestration would be extremely slow, working on geological times scales--perhaps the inhabitants can speed this up (by accident?)

Thanks again Lynx Fox (and furthermore thank you for your patience), it is much appreciated.
It is indeed problematic. I'd prefer to call in poetic license only as an absolute last resort, but I don't want this Earth turning into Mars. Perhaps a thinner atmosphere isn't the answer? Gah!
Anyway, might you be able to expound on your solar storms and carbon sequestration ideas?

Not sure why you are trying to remove atmosphere. Heck is could naturally be that way just by forming with fewer volitiles. But I'll continue.

Our magnetosphere prevents deep penetration from current solar storms only stripping a bit of the upper free hydrogen. But if it was weaker, or if our star went through a period of particularly strong solar storms producing solar winds thousands of times more energetic, like we think happened early in our solar system's history, the planet could lose a good part of the atmosphere. Not sure how it would be to be outside for your survival, but imagine auroras so bright you can see them during the day and can read by them by night at the equator.

Thanks again Lynx_Fox! Well, without wanting to give away too much of the plot, I'm dealing with a very different Earth; one that still sustains human and animal life (although exactly what animal life I haven't yet found out) but is distinct enough for have evolved differently.