[jisee]

700 million years ago, according to Science, the Earth was covered with a mile of ice, pole-to-pole. (Can you believe it?)

How the heck did that happen?

Well, They say it happened because all the continents had randomly accumulated near the equator. (You know how they wander about, drifting Continentally). Which, They say, resulted in an unprecedented level of ‘weathering’ (the reaction between rock and air, and water) that sucked the carbon-dioxide out of the atmosphere.

That’s the cause: weathering sucked the carbon-dioxide out of the atmosphere.

(I know, my attention span is waning, even as I write this)

So what?

So… without the Greenhouse Gas(s), the temperature dropped. Ice-world. Pole to pole. Imagine it. Equatorial glaciers.


So the Earth was a snowball – pole to pole. For millions of years.


How did Life survive that? (I asked myself.)

The short answer is; it just did, as bacteria. It just toughed it out, living in the ice, eking out existence from the sun, or even, completely in the dark, from rock itself. Life it, seems, will find a way. These life-forms are still doing these unlikely things to this day. So, we know they can.


99% of life died. There were ice-living survivors (which are still findable in the deep ice caves of today).

From this bacteria evolved you.


Oh yes, the question. (Got carried away with the grandeur of the thought)

The question: according to Science, the melt of the global snowball allowed, or seemed to produce, multi-cellular creatures. After the Big Melt, Life exploded into forms that we could see with the naked eye. Without it, we wouldn’t.

To quote one Australian scientist: “If it hadn’t been for this (global) ice-age, it would have been slime-world forever.”

Is this true?

Should this be a factor in the Drake Equation?

[lionsiy]

(You may be wondering what caused the Big Melt - Science says it was vulcanism - a lot of volcanoes, and the gas they emitted. It all seems a bit random, dunnit?)

[RsQhyZyR]

A less frantic approach to the matter of the Proterozoic snowball earth can be found here

http://www.meteo.mcgill.ca/~tremblay...ature.2000.pdf

and here

http://isites.harvard.edu/fs/docs/ic.../TerraNova.PDF

and here

http://www.ndsu.nodak.edu/pubweb/~as...ag_Science.pdf

[SQiTmhuY]

Now Geoff, what I did, was summarise my sources, to save you time, and yet give you the ghist. I put a bit of effort into doing that.

[Corporal White]

Why was it going to remain a slime planet, without the snowball? Is slime really that dominant?

[AndreasLV]

>> Why was it going to remain a slime planet...

I'm guessing that he meant that only single-celled life could exist in Ice World. Like the cyno-bacteria that party-on in the ice to this today. The melt of the Ice World made more energy (and nutrients) available, suddenly.


(Incidental fact: sea ice is the most reflective natural thing, open water is the least reflective thing).

[Frjrbefd]

Now Geoff, what I did, was summarise my sources, to save you time, and yet give you the ghist. I put a bit of effort into doing that.

No, what you did was not give sources, blurted out a few (probably misunderstood) concepts you picked up somewhere, and waved your hands around a lot. Were you referring to the carbonate caps wrt the removal of C)2 from the atmosphere? There's still a lot of discussion about where those oddities fit in. The accelerated weathering, from my reading, came after the melt, not before.

[Iphone]

Geoff retorted:

>>No, what you did was not give sources, blurted out a few (probably misunderstood) concepts.... and waved your hands around a lot"

Cool, wasn't it? (No 'concepts' - just facts as Science Says)

[styhorporry]

>> Why was it going to remain a slime planet...

I'm guessing that he meant that only single-celled life could exist in Ice World. Like the cyno-bacteria that party-on in the ice to this today. The melt of the Ice World made more energy (and nutrients) available, suddenly.


(Incidental fact: sea ice is the most reflective natural thing, open water is the least reflective thing).

Oh, I would have taken it as given that we would have been unlikely to have evolved on an ice planet. I thought the the theory was that without the snowball there wouldn't be multicelluar life?

[tattcasetle]

Geoff retorted:

>>No, what you did was not give sources, blurted out a few (probably misunderstood) concepts.... and waved your hands around a lot"

Cool, wasn't it? (No 'concepts' - just facts as Science Says)

But, you see, it's not all what science says. Some of it is (the vulcanism and outgassing) but the big loss of CO2 from the atmosphere happened some time after the glaciation. Much of the other is what someone, somewhere, thinks science says, when most of the science is still scratching its head and saying FIIK. What caused the interglacial period? Still pondering. Was methane involved? Still pondering. What did phosphorus have do with it? Still pondering. How did the carbonate caps form, because so much CO2 in the air should have made the oceans acidic? Still pondering. And so on.

It's not cut and dried by any means, because people have only been seriously considering the possibility for about 30 years.

[WGRocky]

>> I would have taken it as given that we would have been unlikely to have evolved on an ice planet.

The idea is, that the Earth *became* an ice world, after Life evoled.


>> I thought the the theory was that without the snowball there wouldn't be multicelluar life?

Indeed,

[mylittlejewelaa]

> 700 million years ago, according to Science, the Earth was covered with a mile of ice, pole-to-pole. (Can you believe it?) How the heck did that happen?

As an alternative possibility, I've been studying the Kepler spacecraft light curve data from lots of stars recently, and one thing that's become clear is that there are very big long term variations in the light flux levels from most if not all stars. This is quite independent of the short term variability from star-spots and cyclic variations. I see no reason why the Sun's light flux couldn't have varied by quite a lot over a long period of time as a function of, for instance, fluid dynamic convection patterns in its interior.

> You may be wondering what caused the Big Melt - Science says it was volcanism - a lot of volcanoes, and the gas they emitted.

Yes and no. Volcanism yes, gas no. Instead, it was supposed to be the dust - powdered rock - spewed from volcanoes that settled on the surfaces of the ice turning it black. Black absorbs more heat than white and so melted all the ice underneath it.

> How did Life survive that? (I asked myself.) The short answer is ...

... that there were always parts of the deep ocean that were liquid. For a modern analogy consider the lakes at the bottom of the Antarctic ice cap today. Lakes like Lake Vostok. Also, deep within the earth was liquid water - temperature increases with depth and it doesn't take too much depth to push the temperature up above freezing.

> according to Science, the melt of the global snowball allowed, or seemed to produce, multi-cellular creatures. After the Big Melt, Life exploded into forms that we could see with the naked eye. Without it, we wouldn’t.

Um, which snowball Earth did you have in mind? There were several. You probably mean the most recent one, about 650 million years ago. Earlier snowball Earths did not trigger a plethora of multi-cellular creatures. But if I remember rightly, metazoa existed before the last snowball Earth. The so-called "Cambrian explosion" occurred after an extinction event linked to volcanic eruptions, nothing to do with snowballs. The "Avalon explosion" of Ediacaran fauna was about 570 million years ago, that puts it well after the latest snowball Earth had ended.

To put in a nutshell, I don't see any connection between snowball Earth and multi-cellularity.

> Should this be a factor in the Drake Equation?

The transition from single-celled to multicellular life should be in there. It only happened once on Earth that we know of, and happened a very long time after life first developed on Earth. But we need to be aware of the word "multi-cellular" here, it means that different cells have different functions within a single individual. It has nothing to do with the number of cells in a single individual, or the physical complexity of shape or movement of that individual.

I see a connection between multi-cellularity and food supply. Multi-cellularity can only develop in an environment where are no evolutionary selection processes due to starvation. Multicellular life is great at protection from predators, but early multicellular life had an abysmal surface-area to volume ratio compared to bacteria and so its absorption of nutrients through the cell walls was slowed down enormously. That was the evolutionary barrier that it had to break.

[appabessy]

I'm still not getting why the snowball, where most of life was wiped out, was needed to encourage multicellular life. Why couldn't it evolve without that stage at all?

[jstizzle]

maybe a bottleneck boxy. all the competing slimes, or nearly all, wiped out. left niches for multicellular to evolve into. like mammals and dinos.

i dunno.

:-)

[pouslytut]

To quote one Australian scientist: “If it hadn’t been for this (global) ice-age, it would have been slime-world forever.”

Is this true? Do you have a reference for the quote or name for the scientist? Might be helpful to see more context with it. Thanks.

Actually, don't worry I've found it - comes from here and the scientist is Jim Gehling.

Gehring works on Edicarian biota, and emphasises the importance of new forms in this period for the importance of metazoan life relative to the later diversification in the Cambrian. See eg here.

[Narkeere]

I think the main difference between the OP and the picture presented in Geoff D's links is that most people think that the 'snowball Earth' (if it happened) retained an area of unfrozen/partially frozen water around the equator, even though there was land glaciation at those latitudes ie it was a 'slushball Earth' rather than a full snowball. There are some people who argue for a hard snowball though (and then there are quite a few people who argue it never happened like that at all).

this goes to Geoff's other point - while these subjects are all very definitely ideas that are widely canvassed, I don't think there is anyone who claims them as absolute facts. Even the strongest supporters of the snowball Earth theory (like Hoffman) cheerfully admit that there are still main unknowns and problems.

See, the following quote from this review article on the period:

This list of papers in support of or opposition to the snowball Earth hypothesis is too long to review in full in
this chapter.