[Stormkeeper]

Well. If you want a slow planetary catstrophie, it would entail that it starts quietly, so that no one at first notice whats going on.

Say plants are growing slower and slower each year, because of the depletion of natural minerals they require. No one would notice if the rafflesia took a year or a year and three months to bloom. It would only be noticed when crops start to take much longer to produce. As a result, oxygen production is decreased, and slowly the atmosphere of Earth would grow thinner and thinner. Because of the thinning atmosphere, less ozone is being replenished, and eventually, the ozone layer will die out, exposing the earth and humans to deadly UV radiation.

Or maybe the melting of the polar ice caps cause a slow shift in the climate, a la Day After Tomorrow ( i think ), only at a much slower rate. The overall lowering of the Earth's temperature causes the Earth to slowly and irreversibly sink towards an Ice Age. The people have to leave Earth because of the Ice Age which will kill anything on the planet.

Or the outer core of the Earth is starting to freeze at an alarmingly fast rate, causing the Earth's magnetic field to grow all screwy, causing a geomagnetic reversal to take place. At this point, you can come up with reasons for kicking humans off the Earth, because the exact effects of a geomagnetic reversal are unknown.

If you want more, I can always think up more.

[FUBAR-BDHR]

Well if you want something that's hard to explain here's one.  An approaching rogue blackhole.  How fast it's over all depends on where your looking at the destruction from.  So basically Earth and the rest of the universe would see the destruction at different times.  It could take days, decades, thousands of years depending on how you see it and how long you are near the event horizon. 

[Stormkeeper]

... Wouldn't Mars' orbit put in in danger from the same black hole too?

[Excalibur]

Unless you had a really small black hole just the right size to destroy Earth...but then where would it go? Into the sun? and gets vapourised...

[Stormkeeper]

I still think ecological disasters will be your best bet though, Mars.

[General Battuta]

Unless you had a really small black hole just the right size to destroy Earth...but then where would it go? Into the sun? and gets vapourised...

No, it would eat the sun. Black holes don't vaporize.

And, actually, you might be able to justify a hole that small. I'm not sure how fast it'd evaporate.

[Bob-san]

Unless you had a really small black hole just the right size to destroy Earth...but then where would it go? Into the sun? and gets vapourised...

No, it would eat the sun. Black holes don't vaporize.

And, actually, you might be able to justify a hole that small. I'm not sure how fast it'd evaporate.

It wouldn't take very long, I don't think.

http://xaonon.dyndns.org/hawking/

A black hole with a single Earth mass would have a radius of approximately 0.8865 centimeters. The temperature of the black hole would be approximately .02 degrees kelvin, and luminosity would be 0.000000000000000009998181 watts. And lifetime? 5.668638e+50 years... I stand corrected: quite a freaking long time!! For the size, however, we'd be safe. I think. Surface gravity would be 516,931,900,000,000,000 earth gravities. Wow. Just... wow.

Now then: a single solar mass black hole would have a radius of 2955 meters. Surface gravity would be 1,550,796,000,000 earth gravities (.000300000058% that of the prior 1 Earth Mass black hole). Temperature would be 0.000000062 kelvin too--so much, much colder. Finally, lifetime would be 2.099496e+67 years. That's an enormous amount of time--much more than that of the "micro"black hole.

[karajorma]

Thing is you don't need an earth sized hole, you just need one large enough that it can swallow mass at the same speed it loses it as radiation. Now you just say that a LHC type experiment created such a thing and then went wrong. The mass is slowly eating the Earth. Mars would be completely unaffected by such a black hole since its final mass would be about the same as the Earth or less.

A supervolcano is a possible option too but if the technology exists to warm Mars to the point where it can be terraformed then it could no doubt more easily be used on Earth.

[Odd Writings]

Or what about a nearby star going kablooie and giving us about 7 years before the shockwave hits?

...hm. doubt that Mars would survive that either.

There IS one thing you could use instead of disaster, though. what if the Mars rovers etc. found alien tech on Mars? Like hell that the world would not want to be there post haste.

And how would you know it had exploded seven years in advance? It's gonna take light seven years to reach us, and the neutrinos will be right behind that.

:innocent: Oh, idunno...I mean it isn't as if there's maniacal geniuses about that could do such a thing, right? Right?

*crickets chirp, tumbleweed flits past*

...and it would be too much to hope for a random Sathanas fleet do explode a star?

Drat.

Oh well; it was worth a try, right?

[Spicious]

And how would you know it had exploded seven years in advance? It's gonna take light seven years to reach us, and the neutrinos will be right behind that.

Which would pass straight through the Earth barely causing any noticeable effect at all.

[Snail]

Unless you had a really small black hole just the right size to destroy Earth...but then where would it go? Into the sun? and gets vapourised...

That's almost as stupid as my dad's "When you go in the bath you drown the bacteria" comment.

[General Battuta]

And how would you know it had exploded seven years in advance? It's gonna take light seven years to reach us, and the neutrinos will be right behind that.

Which would pass straight through the Earth barely causing any noticeable effect at all.

Actually, there's some debate about that -- I've heard from some sources (college profs) that the neutrino flux is actually dense enough to cause serious radiation damage in this case.

Normally, yes, neutrinos are very weakly interacting, but supernovae make a ton of them. I'm not sure if it's enough to actually do any damage.

Thing is you don't need an earth sized hole, you just need one large enough that it can swallow mass at the same speed it loses it as radiation. Now you just say that a LHC type experiment created such a thing and then went wrong. The mass is slowly eating the Earth. Mars would be completely unaffected by such a black hole since its final mass would be about the same as the Earth or less.

A supervolcano is a possible option too but if the technology exists to warm Mars to the point where it can be terraformed then it could no doubt more easily be used on Earth.

Yep, that's the general kind of hole I was thinking of.

[TrashMan]

Or the outer core of the Earth is starting to freeze at an alarmingly fast rate, causing the Earth's magnetic field to grow all screwy, causing a geomagnetic reversal to take place. At this point, you can come up with reasons for kicking humans off the Earth, because the exact effects of a geomagnetic reversal are unknown.

If you want more, I can always think up more.

Actually, a geomagnetic reversal is long overdue, and it's probably already started. the Earths magnetic field is changing already.

[Snail]

It happens every so often IIRC and people don't notice.

[TrashMan]

actually no.
The last one was ...40.000 years ago IIRC.
And it usually happenes every 20 000 - 30 000.

Recent surveys have shown that the southers hemisphere has begun to show more and more anomalies - in that there places where magentic lines are supposed to be coming out, are now becoming places where they go in. In a similar fashion, the norther hempisphere shows sport where the reverse is happening.

Eventually when the shift does happen, you can expect multiple Auerora Borealis to appear on the sky at random, all over the wrold and for compases to go beserk, at least until the poles re-align themselves. It should be a short process.

[Colonol Dekker]

If the film "the core" taught of anything, it's that pacemakers are the first sign to look for. Also that terranaut pilots are hot.

[karajorma]

If the film "the core" taught of anything, it's that we shouldn't watch films like The Core.

Fixed it for you.

[Bob-san]

If the film "the core" taught me anything, it's that we shouldn't watch films like The Core and that I'm a n00b for watching it.

Fixed it for you.

Fixed it for you.

[Flipside]

Well, birds navigate using magnetism, and they've been around for a good few million years, so whatever impact it has, it can't be as severe as some publications are making out.

Could explain what's going on with the Bees, however, since they have more sensor equipment than the FBI Headquarters.

[Mobius]

All birds nagivate using magnetism? Are you sure of it?

(I know many species of them use magnetism to navigate, but all...?)