Two billion years ago, snowball Earth was defrosted in huge asteroid crash – and it's been downhill ever since Scientists studying minerals in the Yarrabubba crater in Western Australia have confirmed the giant pit was formed when an asteroid struck Earth 2.229 billion years ago, making it the oldest impact site yet found on our planet. “Yarrabubba, which sits between Sandstone and Meekatharra in central WA, had been recognised as an …
Piecing together the evidence is important as it helps scientists understand how impact events like the one in Yarrabubba might have affected the atmosphere, oceans, and life on Earth, and what effect future strikes may have.
It's about time that humanity ought to have some kind of plan for when an astroid like this is heading towards earth; if we wait long enough it will certainly happen...
Maybe the only thing we have -->
We don't even have a plan for how to stop mankinds slow destruction of the planet, something that we do have influence over. In fact, we can't even all agree that we are destroying the planet.
I don't think there is much chance of us all agreeing how to protect us from a galactic impact. No doubt someone will come up with some bonkers theory that we were all created out of thin air in 7 days, 5000 years ago, and that this crater has to be fake news as nothing can be that old.
Like happened as a result of those pesky blue-green bacteria who at the time were busy using this new fangled photosynthesis thing with the side effect of burping out toxic oxygen. Pretty well every other sort of life (bacteria and archaea) were anaerobes.
It is thought that the mitochondria in our cells and in every other non Prokaryote (bacteria and archaea) to make the first Eukaryotic cell happened when a large, nucleated bacterium (probably an archaea) tried to engulf and eat some small bacteria who could do oxygen chemistry and failed to digest them.
Even now pretty much ALL of the oxygen chemistry in our cells is done safely inside the double membrane of the mitochondria and the rest of the cell is still anaerobic.
Those blue-green bacteria? still around of course but an early Eukaryotic cell (think amoeba) did the 'engulf bacteria and fail to digest them' thing with those and became plants. After all lying around in the sunlight letting the lodgers make your food sure beats trying to eat things for a living. Not that there aren't freeloading parasitic plants going one better of course.
There's a layer of, essentially rust in the really old rocks. Oxygen levels couldn't rise appreciably in the atmosphere or oceans because all the reduced metals, especially iron had to be saturated with oxygen (rusted) and stop being oxygen sponges. The early Earth had a reducing atmosphere. It was very different from now.
It's thought the oxygen contributed to the global cooling and snowball earth.
Life: futzing with planetary chemistry for billions of years. It seems hominids have been causing global warming and extinctions for a couple of million years. H. erectus made fires for a start and our distant ancestors might have kicked predators like sabre toothed cats off their kills causing their extinction. Even today lions have to put up with landrovers filled with hominids gawping at them while they eat.
I don't think there is much chance of us all agreeing how to protect us from a galactic impact. No doubt someone will come up with some bonkers theory that we were all created out of thin air in 7 days, 5000 years ago, and that this crater has to be fake news as nothing can be that old.
More like 10 million years old. It was fabricated by some colleague of Slartibartfast.
Currently the plan with highest probability of success, is to put your head between your knees and kiss your arse goodbye!
Fortunately, over the last couple of billion years a lot of the rubble whizzing around the solar system has either been swept up by the planets or captured into stable orbits that hopefully won't intercept ours.
Piecing together the evidence is important as it helps scientists understand how impact events like the one in Yarrabubba might have affected the atmosphere, oceans, and life on Earth, and what effect future strikes may have.
I don't thing the future long term effects on the atmosphere, ocean and life on Earth will be of much importance to scientists, or anyone else, if the planet gets hit by an asteroid carrying enough energy to punch a 70-kilometre diameter hole in it.
After civilisation and agriculture have immediately collapsed, almost all of humanity will be dead within a year. The few scattered long term survivors eking out a stone age subsistence existence will have neither access to the research nor the resources to make use of it. Better to prevent the strike in the first place.
"Better to prevent the strike in the first place."
I think the current destructive capabilities od the entire planet need to increase by a few orders of magnitude to deal with an incoming object big enough and energetic enough to punch a 70 Km hole.
Or if deflection is the plan, we'll need a bigger rocket.
"I think the current destructive capabilities od the entire planet need to increase by a few orders of magnitude to deal with an incoming object big enough and energetic enough to punch a 70 Km hole"
If the destructive capabilities of the planet increase that much, we're unlikely to survive long enough to need them to deal with an asteroid strike.
"The few scattered long term survivors eking out a stone age subsistence existence will have neither access to the research nor the resources to make use of it."
Stone age? Hardly. Steam age.
*IF* Chez Jake should survive (I'm not holding my breath) we can probably survive long-term, assuming the climate cooperates. Not looking forward to it, though. But I'm not losing sleep over the concept, either. The math(s) says I'm more likely to win the lottery than I am to die in an asteroid strike. And I don't even play the lottery ... it's that math(s) thing again.
Earthquakes, now ... Not if. When. We're ready. I hope :-)
It's about time that humanity ought to have some kind of plan for when an astroid like this is heading towards earth; if we wait long enough it will certainly happen...
Plan. 1; spot anything in an orbit that is likely to impact earth. NASA already do this (https://en.wikipedia.org/wiki/Sentry_%28monitoring_system%29).
Plan 2, when we discover that something is going to hit the earth then we have about a hundred years to figure out a solution then start doing something about it.
The most obvious solution to be frank is to either shine a laser at it which could slowly push it off course, or toss a very large contact fused nuke at an intersecting orbit if people are inpatient and want to see a big bang.
Even if said nuke failed to reduce the asteroid to it's constituent atoms it would act as an Orion drive and push the asteroid off course somewhat. In astronomical terms space is very big, and the earth is very small so a tiny course change far enough out would generate a miss, and give humanity another few centuries or millennia to deal with the problem.
Plan 2, when we discover that something is going to hit the earth then we have about a hundred years to figure out a solution then start doing something about it.
I am afraid your time frame errs a bit on the positive side. Depending on a couple of factors, it will more likely be something between 100 days and 100 weeks.
Thrusters (Ion drive type stuff, not rockets) or ablative methods like lasers/solar reflectors/surface reactors are the only methods we have that will stand a chance of working on a large object.
The rocket fuel to payload equation is a really harsh mistress, and lifting enough fuel to push something that is large and fast moving with rockets is just not feasible unfortunately. Lasers could deliver energy to the target without using fuel to get there, though it would take a bunch of very powerful lasers to do the job. Concentrating solar light would take a huge set of reflectors to capture and focus the energy, but the sun runs 24/7. The one nuclear option would involve sending what is in essence a reactor not a bomb, and would have to heat the target and essentially use it's mass as fuel to be efficient enough to be worth sending.
Bombs are too hard to place in a way that most of their energy isn't wasted, and ensure the object does not break up in a way that makes things worse. Of course, some would say if we are all gonna die we might as well put on a big fireworks show.
Right now the plan is essentially "deal with it" which when presented with that level of threat amounts to "When in danger or in doubt, run in circles, scream and shout"
Actually stopping such an event, while difficult and expensive, does seem worth the effort.
" it might have helped create conditions to support life" - err ... the oldest evidence of life is from 3.5 billion years ago. Life had been going strong for at least 1.3 billion years when that pebble hit. Another one isn't going to sterilize the planet either (bacteria are *tough*).
Right there, of course.
2.229 billion years of erosion will tend to mask the most stubborn of asteroid induced blemishes. You'll have to go on-site and dig. Or bounce miscellaneous bits of electromagnetism off it from enough height, ranging from millimeters to thousands of kilometers, with the proper detectors to read the reflected signal.
Yeah, the picture in the post points to something that is very misleading geologically speaking. Also keep in mind that 2.2 billion years is a preposterously long span of time. All of the Earths landmasses have slid all over the place in the mean time, ripping apart, crashing back into each other, and ripping apart again. Those processes happen on scales of millions of years, and that time period was in the period of breakup between two supercontinents.
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Mars' biggest problem is that it isn't large enough to sustain a proper atmosphere. I can't remember the exact equations (it has been a number of years since I did any proper astrophysics), but you can calculate the rate of atmosphere loss by working out the escape velocity, working out the boltzmann distribution for the speed of molecules in the atmosphere, and seeing what percentage of those is above the escape velocity. Because Mars is smaller than Earth, the escape velocity is higher. It's only because it is also colder, that it has any atmosphere at all, and the fact that it's mostly CO2, the moelcules of which are heavier (and thus slower moving) than the N2 and O2 that makes up most of our atmosphere. Incidentally, this is why helium is a rare and valuable resource on Earth, despite being the second most abundant element in the universe, and why we shouldn't be wasting it on party balloons - with an atomic mass of 4, the average speed of a helium atom in the atmosphere is above the Earth's escape velocity, so it "boils" off the top of the atmosphere into space. (The same applies to hydrogen, but H2 is pretty reactive stuff, so it doesn't tend to stay in the atmosphere for long enough for any appreciable amount ot be lost to space.
To add - the equations concerned, IIRC, involve taking into account the thickness of the atmosphere, mean-free-path for gas molecules, and surface area of the top of the atmosphere, which kind-of ignores the fact that the atmosphere of a planet doesn't really have a "top", and probably isn't spherical, due to rotation, but then you're getting into the territory of the old physicist jokes about spherical cows in a vacuum...
Mars' biggest problem is that it isn't large enough to sustain a proper atmosphere
It's worse than that - the core of Mars is either cold or not big enough to produce a decent magnetic field to protect against the solar wind blowing away the atmosphere. So, even if you somehow increased Mars' mass, you'd still lose the atmosphere..
Terraforming is *HARD*.
Actually, there is some daylight here, as part of the complex of atmospheric loss is that the upper atmosphere is being stripped off by solar wind due the aforementioned lack of an earth like magnetic field. If it had a stronger field the losses become manageable to some extent. Creating a field is actually MORE feasible than the effort to establish a proper atmosphere.
It's also a terrible plan, as there is no justifiable reason to create an atmosphere on mars. We can inhabit it the way it is, living on the inside, and on the surface in sealed structures. Plenty of building materials available there.
The surface should be for photovoltaics and greenhouses. We should save whats left of Mars's water and atmosphere for use inside, not waste it outside. Because the next closest source of atmosphere is Venus...
and she's a caustic bitch.
Top it off with what? and from where?
Yes, the losses are a long term problem, just like terraforming would be a long term project. A multi-generational undertaking is not something we should do while based on short term thinking. That's how we got in our present mess in the first place. The solutions we choose should be sustainable going forward and not create a huge problem for someone else to deal with.
If we go to mars we need to adapt to it, not it to us.
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Something else that contributes to the loss of atmosphere on Mars is Phobos as it is scraping the upper reaches of atmosphere. To really terraform Mars, the mass should be increased by a lot and Phobos should be removed, two problems with a common (partial) solution: crash Phobos into Mars (preferably in small pieces), together with a lot of comets and small asteroids.
After that, strengthening the Martian magnetic field is another problem, but solar wind isn't as much of a problem on Mars as it is on Earth. With roughly double the distance from the sun, it is roughly a quarter as strong.
Incidentally, this is why helium is a rare and valuable resource on Earth, despite being the second most abundant element in the universe, and why we shouldn't be wasting it on party balloons
Helium is obtained from natural gas extraction; sticking it in party balloons might be "wasteful" in a strict sense, but pretty much the only other option is to just vent it, which is wasteful by anyone's definition. And even when we do run out of dead dinos, helium's a natural product of radioactive decay; pass alpha particles through a long enough pipeline to eliminate beta and gamma radiation and you've got a perfectly serviceable production line.
Also He-He gas is a byproduct of fusion if we get that going at scale. Still, it's dumb to waste what we have easy access to now, instead of storing it.
BTW our current helium crunch was engineered. They changed the protocols to stop replenishing the US helium storage (Pumping it under an old geologic formation in Texas through old gas wells I believe) because it was getting too cheap on the open market. That was years ago. The prices came up, but the replenishment didn't. So the prices are still going up.
Due to the finite supply, no readily storable helium should be vented unless the practical storage is also full. At least pump it back where it came from so someone else can extract it later. If the prices are a problem let the government restrict how fast they let out the supply, free market be dammed.
Burning the forest down to make the tree in your front yard valuable is always a terrible plan.
@the other Alister:
Only if your nuke is big enough to dig through the surface, techtonic plates and a fair bit of the core. If we're gonna restart Mars' core, its gonna take a heck of a bore hole and all the nuclear waste we here on earth have generated already, and likely about another 500 years worth of FBR waste from the re-escalated arms race. And that depends on Mars actually having a nickle/iron core like Earth's. A long time ago in a small town far away I and about 4 other engineering hopefuls got very drunk and discussed this. It was rather weird.
Only if your nuke is big enough to dig through the surface, techtonic plates and a fair bit of the core.
No problem. I suggest the Geostationary Orbital Nuclear Excavator. Plus there's some prior art, like the Sedan crater.
A long time ago in a small town far away I and about 4 other engineering hopefuls got very drunk and discussed this. It was rather weird.
IMHO, normal for engineers.. Although this may skirt dangerously close to civil engineering. But those sorts shouldn't be allowed to play with nukes. Remember, mechanical engineers build weapon systems, civil engineers build targets.
Also curious about the nickel/iron core. Like we've got one, why wouldn't Mars? And if Mars has one as well, what made it stop?
>Remember, mechanical engineers build weapon systems, civil engineers build targets
Of course, before the mechanical engineer can build his* weapon system, he* needs a civil engineer to build the factory it's made in.
I may be a little bit biased.
Yes, it's the Hi-vis jacket.. yes, and the hard hat.
Or her/she, of course.
Of course, before the mechanical engineer can build his* weapon system, he* needs a civil engineer to build the factory it's made in.
Nah, cave, duct tape, hammer, we're good..
Yes, it's the Hi-vis jacket.. yes, and the hard hat.
Ok. Ok.. so there would be some.. soil engineering value I guess*. Like not having the hole collapse before we've run out of nukes. Or reached the core. I'm thinking going back to basics on that, where yield's based on log(n) where n=yield in gigatonnes. Some kind of logarithmic progession might be safer than exponential I guess. Plus I reckon if we could convince the world to donate their warheads to this project, with some creative accounting and a well provisioned bunker, the project could be self financing.
*So.. architects? Get a select few to be responsible for 'marking out the target' on the surface. Left a bit.. left a bit.. hold it there!
Architects? Wash your mouth out with soap, young man!
I was thinking more along the lines that we'd need a target marker. But having performed similar* experiments as a child, problem with digging a hole this way is dealing with the ejecta. So by the time it'd get deep, it'd also be getting rather wide. Yey! We've found the core! But.. resculpted Mars into an interesting concave shape. And similar problems with the idea of driling. Like dealing with all the spoil created. Which movies like Core kinda ignored, amongst it's many other sins.
All fun to think about, like using more sensible charges to do seismic surveys. Or find caves to dwell in to avoid radiation, but then would Mars have decent caves given a lot get formed from hydrological activity? I still think it makes a lot more sense to stage from the Moon, because if we can learn to survive and thrive there, Mars should become a bit simpler.
*Luckily this was in an era when an interest in chemisty didn't involve visits from anti-terrorist types. And I still have all my fingers!
used AI to show that the mass extinction at the end of the Devonian was no such thing - it took 50 Million years! I wonder if closer examination of the data for 2.229 billion years ago may need to be looked at in similar detail. While I would not be surprised with short term (~decade) temperature rises due to the asteroid strike I'm not convinced it was sufficient to melt through the miles of ice to reduce the planets albedo enough to end the snowball earth on its own.
Otherwise brilliant work - its shit like this with big bangs and catastrophes that gets kids interested in hard science!
Soil, the photo is badly labelled. The only surface evidence is a small eroded hill that is the remnant of the central peak. The rest of the crater structure is eroded away. The remote infrared sensing seems to allow some estimate of size. I note Wolfe Creek crater is now only half its original estimated age, being only 120,000 years old. Some good recent small craters just off the road to Ayers Rock at Henbury well worth a visit. Apollo moonshot astronauts went there for the intersecting crater geology example. Oh yes, watch out for snakes. The local browns are fairly lethal {G} Remember, in Oz, everything is trying to kill you
> the impact may have increased global temperatures to melt the glaciers
BS, this is impossible. Nothing natural caused that. Your data is wrong or has been meddled with by a denier.
> After the impact, glacial deposits are absent in the rock record for 400 million years. This twist of fate suggests that the large meteorite impact may have influenced global climate.
Impossible. Your data is wrong or you, or someone who works for you are climate deniers.
> Numerical simulations of the impact suggest that the blast could have vaporized the water locked in the ice covering Earth to release up to 87 trillion kilograms of water vapor into the atmosphere. As a greenhouse gas, the water vapour would have absorbed and emitted thermal energy to raise temperatures globally.
More total BS. Water as a greenhouse gas might be true, when its a gas, but c'mon be serious here. Are you REALLY going to try and
convince the world that our man made climate change may be the only thing that will save us from returning to a harsh frozen tundra?
We all agree that climate averages out to be static (with some slight variation due to chaos theory, butterflies etc). ALL change in climate is caused by man and can only be controlled by man. To save us from the firestorms that will ravage the planet in 10 years we need to turn off all power generation and manufacturing NOW. Ok use the nuclear plants and turbines while they still work but don't dare build new ones. We need to return to small communities living in mud/reed huts. Ok, maybe wooden houses using wattle and daub (that stuff is amazing, it even meets current british standards for fire resistance as long as its maintained).
Sorry but we have to rough it, no burning of anything to make fires for any reason. Perhaps we can find a way to use the sun to boil water for cooking. The gravy train has come to the end of the track. After a while there will be a correction on the number of humans that can live, then maybe they can light a fire.
I may be AC but I'm not trolling. I'm AC because most people pretend to follow the leader without actually accepting that they should to do so. Its like allowing people to have normal knives in the home while watching all the kids cut each other up. The solution is to ban them and replace them with safety knives. The old knives will go blunt and become useless eventually. But because they want to slice this or chop that they cover their ears and go "lalalala" when the news comes on showing another stabbing as they know they must make the difficult decision of banning knives but wont do it because "its difficult", "its inconvenient".
Its the same mentality that infests most of the non-denier population. The real deniers are public and happy to be so, nice for them. Most non-deniers come across as being in denial about the reality of the situation and its solution.
This is what needs to be done, we all know it. Greta herself has said that net zero wont cut it, she says it must be total zero.
You cant use science to cheat a way out of this. We know the causes and we have the off switch. Any tech we try to implement to cheat this will release more CO2, and burning emits CO2, any manufacturing process that makes a wind turbine or solar panel emits CO2 (plus what the hell do you do with the old broken ones?) so no "miracle tech" can be done till levels are much much lower, say 100ppm, then there is wiggle room to make stuff assuming we remember how to do it as it will take hundreds of years to fix this mess.
I... Sorry. I just built a new Sarcasm-O-Meter and the lecture it's giving me is... ZERO?
I guess I must have screwed something while putiing all those whatchamacallits together... Or forgot to connect a battery to it... Yeah. It must be that!
.
.
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[tinkering sounds - video of a clock handles spinning fast]
.
.
.
FSCK!. Still ZERO.
I think I'll go for a beer.
We all agree that climate averages out to be static (with some slight variation due to chaos theory, butterflies etc). ALL change in climate is caused by man and can only be controlled by man
I am sure this is some kind of elaborate joke, but just in case: no-one who knows anything about climate thinks that. There were, for instance, ice-ages in quite recent history about which we have really good data, and things like the snowball Earth much longer ago, about which we have much less good data. Climate is not and has never been static. It's just that sometimes it changes fast enough to kill a lot of the life on the planet, and sometimes that rapid change is caused by the life on the planet. As an example of that the rate of change of temperature in the last deglaciation (not caused by humans) was about a degree in 850 years: the current rate of change (largely caused by humans) is about 10 times that.
Snowball earth was more likely a consequence of albedo rather than lack of H2O/GHG in the atmosphere. The initial vapourised water would quickly precipitate out as snow if that was the only consequence of the impact. More likely is the dust cloud from such an impact would be the primary driver for change. After a short period of cooling due to dust clouds in the atmosphere, the reduced albedo when the dust finally settled onto the rest of the snowball earth could have driven enough melting to sustain the water cycle as we know it. So whilst the Yarrabubba impact could be linked to the ending of the ice age I don't agree with the how.
Yes. Dust. Any system that has a knock on effect could have results (such as acidification of seas changing algae then changing carbon dioxide or methane sinks/releases). And dust is one that does not get the attention it needs. It can drive the difference in small amounts to massive amounts of sunlight absorption or reflection, and to add the humidity in the air!
I wonder *how* quickly it would precipitate as snow - water vapour can carry a significant amount of heat with it, and would have to cool sufficiently. It probably depends on whether the effect is large enough and long enough lasting for enough heat to be captured by the atmosphere for it to be self-sustaining. In a big-old-impact, there would undoubtedly be several effects in play at the same time, but I wouldn't be so quick to rule out water vapour staying in the atmosphere for a significant enough time, especially if it's in the upper atmosphere.
I do agree though, that melting kilometres-thick ice is going to take more than a couple of years, unless you're putting a lot of energy into the system...
If you put all of the energy that arrives on Earth from the Sun into it you can melt the current Antarctic ice-sheet in about a year and a half. That's obviously absurdly implausible. In real life it takes thousands of years: probably tens of thousands to millions to come out of something like snowball Earth.
Volcanoes are a tricky one because depdning on the type of eruption, they can either relase a lot of gases that are direct or indirect greenhouse gases, or they can inject a lot of dust into the upper atmosphere, which can have a cooling effect e.g. the postulated cause of the little ice age, or they can eject a large amount of tephra, which would reduce the albedo of ice from nearly 1 to nearly zero (depending on the type of magma involved, for example the volcanoes in Iceland eject oceanic basalt, which is nearly black, whilst volcanoes on continental crust eject comparatively lighter material). All in all, I'd be inclined to say the incerased volcanism would have seen a short-lived cooling effect, balanced out by the short-lived warming effect of the vapourised ice, and an additional warming effect due to both the ejecta directly onto the ice*, and the dust and ash that would spread further and settle onto the ice decreasing the albedo.
*Surprisingly, volcanoes are surpisingly bad at completely melting ice. The volcanoes in Iceland that are covered by glaciers year-round tend to melt only the ice directly above the erupting vent, and often not all the way to the surface. The effects this actually produces are flash flooding when the water breaks through the ice (often tens of meters high) and the collapse of the roof of the void created when this happens. The bulk of the glaciers still persist, however. When we're talking about kilometres of thickness of ice, as in "snowball Earth", many volcanoes may never have managed to erupt all the way through the ice sheet at all.
When we're talking about kilometres of thickness of ice, as in "snowball Earth", many volcanoes may never have managed to erupt all the way through the ice sheet at all.
This has always been one of the problems with Ice Ages. So it's easy to thow out terms like albedo changes, or Milankovitch cycles.. But to get into one, you'd need a prolonged drop in global temperatures, so a long (in a geological sense) reduction in energy. Which mostly comes from insolation, ie the Sun's energy output. An orbital excursion might do that, but the orbit would need to change by quite a lot to reduce insolation and drop temps.
Volcanic activity has been suggested, but similar problems. So recent large eruptions like resulted in observed effects like 'the year without summer', but volanic ejecta doesn't tend to linger long in the atmosphere before it settles. Other GHGs like SO2 might have had cooling & albedo effects, either as a negative GHG, or acidification killing of a LOT of vegetation.. But which volcano?
Then there's the reverse problem with exiting the Ice Age. So 1g of ice takes 334J to melt, so a collosal amount of energy required, especially as albedo should mean more energy reflected/re-radiated. We know dust has an effect, ie black soot & dust creating melt pools on ice sheets. But how to produce enough dust? And as you say, a volcano melting or erupting through a large ice sheet would need a lot of force/energy. And we kind of have examples in places like Antarctica, where volcanic activity under the ice melts bottom-up and lubricates sheet/glacier movement.
But this is all stuff that needs to be reconciled before CO2 dogma can explain past climate changes, or how it's the 'control knob' for all climate change. Where does the CO2 come from to exit an Ice Age given a lot of know volcanoes don't outgass much of it?
For conventional (ie recent) ice ages this is all pretty well understood. In particular a conventional ice age does not involve ice covering all, or even I think most of, the planet and does not involve the oceans freezing, not even on their surfaces over much / most of their extent. So there's plenty of life and plenty of ocean to do things to CO2. It takes a while, of course – the rate of change of temperature during the exit from recent glaciations would have been so low as to be imperceptible by humans without access to fancy technology and ice cores (about a degree of increase every 8-900 years: the rate of temperature fall when going into a glaciation is even lower).
Snowball Earth is more interesting. To get out of a snowball Earth you need really seriously high levels of CO2 – of the order of 10% of the atmosphere (so hundreds of times the current level). So the question is how that arises and the answer is 'very slowly'. Because the Earth is completely covered with ice, there is no rock weathering process to remove CO2 from the atmosphere. There's also essentially no CO2 extraction by life (there is some presumably, but very very little, since everything, including quite possibly the oceans, is frozen solid). But geological processes still dump CO2 (and methane &c) into the atmosphere. So gradually CO2 levels climb in the atmosphere, until they get high enough that ice starts melting. Exposed land surface and water as a result then has much lower albedo than ice and things then move relatively rapidly (emphasis, probably, on 'relatively': it's possible to come up with scenarios where things move fast on human timescales, but there are plenty where they don't).
But it's gradual: very gradual. The estimate is millions to tens of millions of years for CO2 to build up far enough.
Note that inverse processes over similarly long timescales are one of the reasons why Earth is (almost certainly) not going to end up as Venus (or at least not until the Sun is a lot older than it is now). You can, maybe, get into a situation called a 'moist greenhouse' which is where a lot of the atmosphere becomes water vapour (essentially, you've boiled off large chunks of the oceans). But it seems likely that weathering then gradually pulls CO2 out of the atmosphere (plant life isn't doing it because it's almost all dead) and things gradually come back to some kind of more sane state (whether life survives is a different question: my guess is 'yes, but obviously we're talking single-celled things, not people'). To get to Venus you need to lose the water vapour to space, and it seems unlikely that would happen on Earth. Whether you can (whether humans could, really) plausibly kick things hard enough to get into one of these moist greenhouse states in the first place is another question: some people think you can but I think those views are generally thought to be extreme.
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