Earth's Atmosphere Without Magnetic Field & Geology

[willstaruss22]

Lets say Earth lost its magnetic field 4 billion years ago and lacked geological activity like mars. Would the atmosphere of Earth be comparable to Mars atmosphere? How thin could it have been without a magnetic field and constant geological activity? Thank you.

 

[phinds]

I remember reading that without our magnetic field, our atmosphere would have eventually been blown away by the solar wind.

 

[jbrussell93]

I remember reading that without our magnetic field, our atmosphere would have eventually been blown away by the solar wind.

Hmmm, that's interesting. What about Venus? It does not have a magnetic field but has an extremely thick atmosphere despite being closer to the sun. In this case, the ionosphere is so active that it shields the underlying atmosphere from the solar wind similar to a magnetic field.

 

[phinds]

Hmmm, that's interesting. What about Venus? It does not have a magnetic field but has an extremely thick atmosphere despite being closer to the sun. In this case, the ionosphere is so active that it shields the underlying atmosphere from the solar wind similar to a magnetic field.

Hm ... you make a good point. I didn't think of that, but I checked very quickly on the internet and I did find statements that the Earth's atmosphere would be blown away without the magnetosphere, although perhaps not all of it.

 

[Chronos]

Venus evidently does have a magnetic field as reported by ESA: http://sci.esa.int/venus-express/50246-a-magnetic-surprise-for-venus-express/.

 

[willstaruss22]

Lets not forget Venus has geological activity like volcanic eruptions and constant resurfacing with amp up the atmosphere. I'm saying what if there was little to no geological activity at all.

 

[Chronos]

With replenishment, it might still retain a reasonably dense atmosphere. Of course, that would beg for vulcanism - which would rule out little or no geological activity. I have difficulty visualizing a planet with persistent vulcanism lacking a magnetic field. Any such planet would surely have a very hot [i.e., molten] core if it has active vulcanism, and that core would probably include a significant nickel-iron component, IMO.

 

[willstaruss22]

No I am saying if Earth had little geological activity would the atmosphere be thin like Mars. I am wondering because Earth has the gravity but its also closer to the Sun.

 

[julcab12]

Lets say Earth lost its magnetic field 4 billion years ago and lacked geological activity like mars. Would the atmosphere of Earth be comparable to Mars atmosphere? How thin could it have been without a magnetic field and constant geological activity? Thank you.

We have yet to find comparison that renders a near identical condition. Nonetheless, assuming Earth has completely loss it's magnetic field 4 bly ago considering a 'very few' variables i.e Gravity pull determine the gases that can form an atmosphere and the mass determines the density of these gases not to mention the sustenance of gases(if present) depending on the condition of the planet. All i can say is that it could be thicker at least in principle.IMO^^

 

[Damo ET]

Hmmm, that's interesting. What about Venus? It does not have a magnetic field but has an extremely thick atmosphere despite being closer to the sun. In this case, the ionosphere is so active that it shields the underlying atmosphere from the solar wind similar to a magnetic field.

Apparently, one of the things that Venus doesn't have that we do, is plate tectonics. Without plate tectonics there is no carbon cycle to take the carbon from the atmosphere and lock it back into rock, which then eventually gets recycled into the mantle. The Venusian atmosphere is in the order of 95% carbon dioxide (compared to .5% for us) which has a nasty habit of preventing heat from escaping the surface. So all the light energy that gets in stays in, and all the heat vented from below stays in also.
Using the info from here: http://www.astronomycast.com/2007/08/episode-50-venus/ , I think Venus' situation played out something like this, in the early formation of the planet it got clobbered by a big object which massively altered its rotation. The day length increased to over a year, and with such a long sun exposure time, vast quantities of H2O were evaporated from the surface. This caused the first part 'Global warming' due to the large quantities of water vapor acting as a green house gas. As the global temperature rose, more and more of the surface water evaporated to the point where all the liquid water was baked out of the surface. In the atmosphere, uv light breaks down the water vapor to H2 and O. The H2 is light enough to escape the planet altogether and the O probably combined with Carbon (not sure of the process). Without surface water, plate tectonics would literally grind to a halt stopping the carbon cycle and the removal of the carbon from the atmosphere. With that carbon allowed to stay in the atmosphere, the Green house went crazy.

The Earth being the mass that it is, would hold onto more of its atmosphere compared to Mars if our magnetosphere went away. The composition would be very different though.Damo

 

[phinds]

So all the light energy that gets in stays in ...

I think the word you are looking for here is "most". Clearly not "all" because if that were true, we could not see it, as we do, in the visible spectrum.

 

[Damo ET]

I think the word you are looking for here is "most". Clearly not "all" because if that were true, we could not see it, as we do, in the visible spectrum.

Yes, you are correct. But light that gets 'in' isn't reflected. I probably should have written that 35% of the light energy which falls on Venus is trapped at or near the surface because it can't get back into space.


Damo