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View Full Version : A question about Snowball Earth: was there enough water?

Quartz
02-22-2012, 04:18 AM
As I understand it, the Cambrian explosion is supposed to have been preceded by a snowball Earth. This is allegedly demonstrated by there being glaciers at the equator There's just one thing that puzzles me: was there enough water at the time? There isn't now.

Anaglyph
02-22-2012, 04:41 AM
As in milder glaciation events, the larger mass of water present as inland ice would have been compensated by a lowering of the sea level

Quartz
02-22-2012, 04:59 AM
As in milder glaciation events, the larger mass of water present as inland ice would have been compensated by a lowering of the sea level

Which exposes more land. Which needs more water to become ice to cover it. Was there enough water?

engineer_comp_geek
02-22-2012, 05:17 AM
Think of it this way. The earth's surface is something like 71 percent water. If you took 50 feet of water off of the surface of the oceans, you wouldn't expose that much land. Cover the entire land surface in 50 feet of ice, and that only takes 29 of that 71 percent. Cover it in another 50 feet of ice (for a total of 100 feet) and you're up to 58 of that 71 percent. You can use the remaining 13 of that 71 percent to cover newly exposed land (which would be far more than what you need).

So you could easily snowball the earth even without a huge drop in ocean levels.

Blake
02-22-2012, 05:53 AM
A snowball Earth with glaciers at the equator doesn't mean the whole planet was covered in ice, any more than the fact that their are glaciers in Sweden today means that all of Sweden is covered in ice.

All that a glacier requires to form is sufficient snow and sufficiently low temperatures that it doesn't melt. You don't need to cover the entire continent with ice to produce glaciers, just some of the larger valleys. Even today, much of Antarctica isn't covered in ice, and it sits at the pole.

j_sum1
02-22-2012, 07:00 AM
Even today, much of Antarctica isn't covered in ice, and it sits at the pole.Sorry, I am going to dispute that. The Dry Valleys are a small proportion of the Antarctic landmass. At the pole the ice is more than 3km thick and IIRC about 80% of Antarctica has been pushed below sea level by the weight of the ice. The thought is that the land would spring back of the ice was ever to melt.

Crotalus
02-22-2012, 07:01 AM
Even today, much of Antarctica isn't covered in ice, and it sits at the pole.Really? I thought Antarctica was over 90% ice-covered. Cool facts about Antarctica. (http://faculty.umf.maine.edu/gretchen.legler/public.www/antarcticawebsite/coolf.htm)

Ninja'd by j_sum1.

Snarky_Kong
02-22-2012, 07:55 AM
The surface area of Earth is ~196 million square miles. The total volume of water on Earth is ~330 million cubic miles. Water gains about 9% of volume when it freezes. Taking that excess volume and distributing it over the surface of the planet would result in a layer of ice about 800 ft thick.

md2000
02-22-2012, 09:02 AM
IIRC, in the last ice age weren't sea levels down about 300 feet? (Land bridge almost Alaska to Asia?) glaciers a mile thick in some northern latitudes?

If instead the snow fell steadily further south as the snow line moved towards the equator, eventually all the land surfaces would be covered. Is it NOT a snowball earth if some places only have 10 feet of snow? Like the real world today or 20,000 years ago or the antarctic, some spots would be bare rock, some would have variable snow cover of feet, some would have feet or miles of ice cover. Depends on weather patterns more than the earth's water cover.

Tom Tildrum
02-22-2012, 09:56 AM
As we all remember from childhood, a snowball and an iceball are very different things.

Alka Seltzer
02-22-2012, 10:47 AM
Assuming the theory is correct, the land would have been largely covered in snow, but not necessarily to any great depth. Not all of the land would have been under glaciers, there isn't enough water. This would have had the effect of increasing the Earth's albedo, so that more of the sun's energy was reflected into space. Only a thin covering of ice was necessary to achieve this. The Earth might have looked like a snowball with grit in it, please don't take the term too literally.

Note that at the time of snowball earth, all life was contained in the oceans.

Lemur866
02-22-2012, 11:06 AM
As has been said, at this point there was no multicellular life on land, and only the beginnings of multicelluar life in the ocean. So it doesn't matter how extensively the land was covered by glaciers. What matters is the extent of the sea ice. Covering large areas of the ocean with ice means drastically lowered photosynthesis. If you have permanent icecap over the oceans at the equator, then there will be almost no life left on precambrian Earth. The land is a sideshow.

I guess I don't understand the question of whether there was enough water to allow glaciers at the equator. There's a lot of water on Earth, it's called the ocean.

ZenBeam
02-22-2012, 11:52 AM
Not all of the land would have been under glaciers, there isn't enough water.I don't understand your reasoning for this statement. What are you basing that on?

Švejk
02-22-2012, 02:36 PM
Not all of the land would have been under glaciers, there isn't enough water.

The surface area of Earth is ~196 million square miles. The total volume of water on Earth is ~330 million cubic miles. Water gains about 9% of volume when it freezes. Taking that excess volume and distributing it over the surface of the planet would result in a layer of ice about 800 ft thick.

Alka Seltzer
02-22-2012, 02:37 PM
I don't understand your reasoning for this statement. What are you basing that on?

As you remove more water from the sea, it's level falls and more land is exposed. There isn't enough water to bury the existing landmasses in ice without exposing a lot of new land. Glaciation occurs when snowfall exceeds melting and sublimation over a long period of time. As more of the Earth freezes, including the oceans, precipitation would decrease. The air over Antarctica is the dryest on Earth. I don't see how that could lead to complete glaciation over land.

Alka Seltzer
02-22-2012, 02:39 PM

Snarky_Kong's statement about expanding ice isn't relevant, as the snowball earth theory does not state that all of the water turned to ice. Only the top few meters did, as the Earth's heat prevented most of it from freezing.

Earl Snake-Hips Tucker
02-22-2012, 02:46 PM
. . . [At] this point there was no multicellular life on land, and only the beginnings of multicelluar life in the ocean. . ..
Well, maybe, and maybe not (http://www.sciencedaily.com/releases/2010/06/100630171711.htm?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+sciencedaily+%28ScienceDaily%3A+Latest+Science+News%29). There might have been multicellular life a billion years preceding Snowball Earth, although it was probably a dead end, and our multicellular ancestors are probably more in the timeline of Snowball Earth.

Švejk
02-22-2012, 02:50 PM
What Snarky said *is* relevant (but not even necessary to disprove your point about there not being enough water), but what you are saying is not. The 197 million sq miles includes the sea bed. Obviously, if you distribute 330 million cu miles over 197 million sq miles, that gives you more than 1 mile of ice on every single square mile, seabed and land area alike (I wonder how Snarky gets to 800 ft when there's 5000+ ft in a mile), - and that's not even taking into account that the 330 million cu miles would expand by 9% as the water becomes ice. That a lower sea level would free up land is not remotely a problem for having a world covered in glaciers.

Alka Seltzer
02-22-2012, 02:56 PM
Did you read my point about glaciation and precipitation? The average depth of the ocean is nearly 4km. How exactly does that mass of water get distributed so that all the land is covered in a significant depth of ice?

Švejk
02-22-2012, 03:09 PM
Look, I'm just saying that when someone has pointed out that there's enough water on the planet to cover the entire surface including the seabed with a thick layer, a statement that "Not all of the land would have been under glaciers, there isn't enough water" just does not cut it.

Alka Seltzer
02-22-2012, 04:01 PM
Snarky_Kong's misconception, and yours, is that the snowball earth theory means that all the water on Earth froze. It does not state this, only the top few meters of the sea are thought to have frozen. Even if the sun was switched off, the Earth's internal heat would prevent the seas from totally freezing for hundred of millions of years. The overall sea level can only rise by 4.5 meters if only 50 meters of it freeze. That's the volume you have to play building blocks with, not the total volume of the oceans. There is not enough water because most of it is still in liquid form.

It's a dynamic system. To expand on my points about glaciation and precipitation, glaciation occurs when snowfall exceeds ablation (melting and sublimation). In a completely ice-locked world, precipitation would be very low. The sun's energy cannot sublimate as much ice as it can evaporate warm water. It's ability to clear snow from terrain features that rise above the level of the glaciers would be undiminished. The low lying land might be completely glaciated, but it's not possible to transport enough ice to bury all the mountains. As I said above, the Earth might look a bit like a dirty snowball, with mountain ridges peeking clear of the ice.

ZenBeam
02-22-2012, 07:43 PM
As you remove more water from the sea, it's level falls and more land is exposed. There isn't enough water to bury the existing landmasses in ice without exposing a lot of new land. Glaciation occurs when snowfall exceeds melting and sublimation over a long period of time. As more of the Earth freezes, including the oceans, precipitation would decrease. The air over Antarctica is the dryest on Earth. I don't see how that could lead to complete glaciation over land.Try putting some numbers to your argument. From this document (PDF) (http://humandimensionsofinsectconservation.files.wordpress.com/2009/06/lemelin-dragonfy-tourism-encyclopdia.pdf&sa=U&ei=B5VFT7jgENCosAK63LzDDw&ved=0CBMQFjAA&usg=AFQjCNFl9X7-SjCBSMZz_XxUEXXPonO4Iw), Deep sea, the portion of the ocean deeper than 200 meters, covers 85 percent of seawater. That, in turn, is 71% of the surface of the Earth. So dropping Sea level by 200 meters only increases the percentage of land from 29% to 40%. The water you've removed gives you somewhere between 61 million and 72 million cubic kilometers of water, or 66 to 78 million cubic kilometers of ice. That's enough to bury the increased amount of land by between 320 and 380 meters of ice, or 1000 to 1200 feet.

There's plenty of water available.

Polycarp
02-22-2012, 10:55 PM
The Snowball Earth theory also is based on the fact that glacial striations from the right time frame (~700 MYA) were observed on rocks presumed to be at low altitude and at low latitudes. I.e., there were glaciers in subtropical areas. But that is based on accurate readings of plate tectonics and of orogenic elevations -- not the easiest thing to confirm that far back.

In any case, we're quite well aware that large portions of Siberia and Beringia were unglaciated even at the height of the Pleistocene Ice Ages, Cold enough that you got LOx on your bagels, yeah, but not iced over.

Also remember that at that time (the Varangian glaciation is the traditional term, though I see Wikipedia is reporting a renaming binge), 95% of the world's land mass was united in a Pangaea-like supercontinent called Rodinia that stretched from pole to pole. We have no idea what conditions were like in the water hemisphere.

Alka Seltzer
02-23-2012, 02:19 AM
There's plenty of water available.

Alka Seltzer
02-23-2012, 02:58 AM
So dropping Sea level by 200 meters only increases the percentage of land from 29% to 40%. The water you've removed gives you somewhere between 61 million and 72 million cubic kilometers of water, or 66 to 78 million cubic kilometers of ice. That's enough to bury the increased amount of land by between 320 and 380 meters of ice, or 1000 to 1200 feet.

There's plenty of water available.

There are terrain features much higher than 380 metres. Glaciation does not occur on steep slopes, the weight of snow builds up and eventually much of it is removed in an avalanche. Here (http://en.wikipedia.org/wiki/File:Beardmore_Glacier_-_Antarctica.JPG) is a picture of a glacier in Antarctica. Notice how it covers the valley between the mountains. If you want to cover a mountain in ice, you have to do it from the bottom up. In that picture, notice that there is a lot of bare rock in view. That's because precipitation is very low in Antarctica, which gives the sun more time to sublimate exposed snow. That's what I'd expect to see on a snowball Earth.

You are correct that exposure of land isn't the primary reason it's not possible to cover all the land in ice, but in the post you quoted I also talk about glaciation and precipitation. It's a dynamic weather system, and lego-brick arguments aren't very useful. As more water freezes the water cycle is reduced.

Quartz
02-23-2012, 05:14 AM
Try putting some numbers to your argument. From this document (PDF) (http://humandimensionsofinsectconservation.files.wordpress.com/2009/06/lemelin-dragonfy-tourism-encyclopdia.pdf&sa=U&ei=B5VFT7jgENCosAK63LzDDw&ved=0CBMQFjAA&usg=AFQjCNFl9X7-SjCBSMZz_XxUEXXPonO4Iw), Deep sea, the portion of the ocean deeper than 200 meters, covers 85 percent of seawater. That, in turn, is 71% of the surface of the Earth. So dropping Sea level by 200 meters only increases the percentage of land from 29% to 40%. The water you've removed gives you somewhere between 61 million and 72 million cubic kilometers of water, or 66 to 78 million cubic kilometers of ice. That's enough to bury the increased amount of land by between 320 and 380 meters of ice, or 1000 to 1200 feet.

There's plenty of water available.

I think that answers my question. Thank you.

Alka Seltzer
02-23-2012, 05:58 AM
I think that answers my question. Thank you.

No, it doesn't. Have you even read my responses?

Snarky_Kong
02-23-2012, 07:20 AM
Snarky_Kong's misconception, and yours, is that the snowball earth theory means that all the water on Earth froze.

There is no misconception. I just answered a different question. The answer to "is there enough water on Earth to cover the planet in ice" is yes. That is what I answered. The answer to "if the Earth cooled, would ice cover the planet?" is a different question that I did not address.

md2000
02-23-2012, 07:40 AM
Snowball Earth would presumably be like Snowball Antarctica - some areas glaciated, some areas snowbound, some areas ice on liquid water, and some areas of somewhat exposed rock. (Like the tops of mountains - scatterings of snow and exposed rock.) Eventually, the seas freeze over everywhere and the process pretty much "freezes in place". After a long time, theory says, volcanic activity creates greenhouse gas levels that tip the heat balance back to temperate, since there is no life actively turning that CO2 to O2.

Is there enough water to do this? Heck yeah... read the numbers posted.

I suspect instead of the typical recent ice ages, where the climate settled at heavy snowfall and mile-thick glaciers down to Wyoming and the Alps, as snowball earth cooled the snow line would keep moving south, creating more distributed, less thick snow buildup - but still deep enough to turn to ice in any flat locale.

As mentioned earlier, since the plates move around and geology has done a lot of work since then, it's hard to be precise. However, one other piece of evidence is glacier-relocated boulders at very tropical latitudes. Also, any active volcanoes probably at least temporarily create clear spots. Since the only humidity would come from sublimation or volcanic activity evaporation, the precipitation levels probably dropped drastically once the oceans completely froze (if they did) so the snow/ice distribution at that point, less glacial movement, is what the planet ended up like.

Alka Seltzer
02-23-2012, 08:44 AM
There is no misconception. I just answered a different question. The answer to "is there enough water on Earth to cover the planet in ice" is yes. That is what I answered. The answer to "if the Earth cooled, would ice cover the planet?" is a different question that I did not address.

Fair enough. Unfortunately, some of the posters in this thread, including the OP, don't understand that. You answered a different question to the one originally asked, which is specifically about the snowball earth theory. Yes, technically there is enough water, but there is no natural mechanism for distributing it in such a way to cover all the landmasses. In much the same way, it would be possible to cover the landmasses in paint if you applied a thin enough coating.

Snarky_Kong
02-23-2012, 09:21 AM
Fair enough. Unfortunately, some of the posters in this thread, including the OP, don't understand that. You answered a different question to the one originally asked, which is specifically about the snowball earth theory. Yes, technically there is enough water, but there is no natural mechanism for distributing it in such a way to cover all the landmasses. In much the same way, it would be possible to cover the landmasses in paint if you applied a thin enough coating.

I can't find any good elevation data to give an answer of how much land the ice would cover if it just swelled from the ocean, so I gave the lazy answer. If the Earth was cooled enough you wouldn't have 800' of ice over the whole planet, it'd be more like 1,000' of ice (about MSL) over 90% of the planet, or something like that.

Lemur866
02-23-2012, 11:19 AM
But it's not neccesary to cover all land masses in a uniform sheet of ice to get a "snowball earth". As has been said, at this point there were no land plants, and no animals at all. To choke off most life on Earth, you don't need to glaciate the land, you just need sea ice at the equator.

Of course in our modern world most of the water in the atmosphere comes from evaporation from the oceans. Freeze over the oceans and no more evaporation, only sublimation. Although there's no saying that you couldn't get summer ice melts--it's not that glaciers and permanent sea ice never melt, it's that they never melt completely.

But even so, your point stands--if almost all of the oceans are covered with ice almost all the time, you're going to have very dry air, which means very little snowfall on the continents, which means you could have places which are below freezing all year round, yet are ice free because the ice sublimates faster than it is deposited.

And of course, there's no saying that the planet was below freezing all year. Plenty of glaciated areas are well above freezing for long periods in the summer, it's just that whatever ice melts during the summer is replaced by an equal or greater amount of snow in the winter, if it doesn't then that area isn't glaciated.

So the "snowball earth" scenario doesn't require that every square kilometer of land was covered by ice. Just that there were continental glaciers in the tropics, which would have meant tropical sea ice. If vast areas of land were cold dry deserts that's not incompatible with the snowball earth theory.