Do you think Tau Ceti e is inhabited?

[caballerodiez]

Hi!

Guys do you think Tau Ceti e is inhabited?

It was recently confirmed (https://twitter.com/i/web/status/1084742558041993216) and it is considered a potentially habitable exoplanet (http://phl.upr.edu/projects/habitable-exoplanets-catalog)

I just made a video about it, just in case someone is interested: https://www.youtube.com/watch?v=Lhfu3DXoOCA&list=PL3RiFKfZj3pv1ZqpFxuZinoGtUGEOankw

[Gargamel]

Moved to S&S Sub forum. 

[Guest]

Edit: oh wow this was moved to Science & Spaceflight and I didn't even notice it, not the place for my not-very-scientific answer

Spoiler

 

Edited February 9, 2019 by Guest

[Gargamel]

4 minutes ago, Aperture Science said:

not the place for my not-very-scientific answer

Which means, now you have to back up your answer with logic and reason, and sources. 

[James Kerman]

Personally I think we need to thoroughly search our own system, in particular deep sample drilling on Mars, Europa, Ganymede, the ice giants and Enceladus, before looking further afield.  Our tree of life requires liquid water and until there is evidence of it on Tau Ceti e there are far better targets for research in our own backyard.

Life on other worlds will remain a mystery until we have a data set greater than 1.

[Bill Phil]

Probably not. I’m pretty sure we’ve thoroughly investigated with radio and it won’t be too long until we can detect waste heat from planetary civilizations (maybe a few decades). If there is life it probably isn’t technologically advanced. We’ll have to wait until we can do better spectroscopy on the atmosphere - among other things - to determine habitability.

Still. That’s pretty close, and a yellow star to boot. Probably a good target for interstellar missions, whenever those happen.

[kerbiloid]

The universe is almost incompatible with high life forms development, so I doubt there is more than 1-2 developed sapient races in our ~1000 ly local oasis between the galactic arms and "too close to center"/"too far from center".
(And even this assumption is mostly based on various ufo events with no clear explanation).

Also as
underdeveloped hunters-gatherers are not numerous, 
modern civilization probably exists for several thousand years then either disappears, or becomes an
overdeveloped one, which probably may exist "infinitely", but quickly losing the animal form and becoming, say, a hivemind hidden in a protected artficial stranger asteroid

so we can more likely meet the more developed aliens than we are, in process of their overdevelopment; and architectural remains of the overdeveloped ones while they were still in animal shape.

So, I would not be too optimistic about native habitants of other star systems.

 

But if there is at least 1 interstellar race, they should probably have numerous outposts here and there. Also on Tau Ceti.

And maybe they use humans as pets, so, lol, maybe some planets which are not appropriate for a local life evolution, are manually populated by humans. We do this in Spore, why aliens shouldn't.
Maybe some of them are allowed to operate with alien ships and other technics, and even visit us to look why should they be thankful to their owners friends.

Spoiler

(Somebody should design the Great Sphinx's head, and unlikely those were insects, lol)

 

Edited February 9, 2019 by kerbiloid

[DDE]

2 hours ago, kerbiloid said:

The universe is almost incompatible with high life forms development, so I doubt there is more than 1-2 developed sapient races in our ~1000 ly local oasis between the galactic arms and "too close to center"/"too far from center".
(And even this assumption is mostly based on various ufo events with no clear explanation).

If we go with that evidence, there will be exactly nine nascent interstellar civs by 2200.

My settings slider in Stellaris says so.

2 hours ago, kerbiloid said:

Also as
underdeveloped hunters-gatherers are not numerous, 
modern civilization probably exists for several thousand years then either disappears, or becomes an
overdeveloped one, which probably may exist "infinitely", but quickly losing the animal form and becoming, say, a hivemind hidden in a protected artficial stranger asteroid

 so we can more likely meet the more developed aliens than we are, in process of their overdevelopment; and architectural remains of the overdeveloped ones while they were still in animal shape.

 

The apes or angels argument.

[kerbiloid]

1 minute ago, DDE said:

The apes or angels argument.

Spoiler

 

[ProtoJeb21]

I’m going to say no. Tau Ceti e has too many problems and is only a fair candidate for potential habitability at best, for several reasons. 

1.) It may not be rocky. While it has a minimum mass of just under four Earths, if the planets are on the same inclination as the debris disk, then Tau Ceti e is somewhere around 7-8 Earth masses. Most rocky planets are no more than 5-6 Earth masses, and at that mass, Tau Ceti e has a greater chance of being a small ice giant. However, there is hope for it. Tau Ceti is very poor in metals, or any element heavier than hydrogen and helium. This actually facilitates the formation of rocky planets because it takes so long for them to form. By the time they’re big enough to start accumulating large layers of volatiles, the hydrogen in the planet-forming disk is all but blown away by the star. So there is a chance Tau Ceti e is rocky, maybe similar to the 7 Earth mass terrestrial habitable zone planet LHS 1140 b. 

2.) Even if Tau Ceti e is a rocky planet, there is one huge problem that could kill its chances for hosting life: the amount of sunlight it gets from its star. The planet receives an insolation about 80% higher than Earth, which may not seem like much, but is slightly less than that of Venus, which is in no way habitable. Tau Ceti e, therefore, has dangerously high odds of being a hellish Super-Venus with a runaway greenhouse effect and no surface water. But like before, there might be a way for things to work in this planet’s favor. If it’s tidally locked — which isn’t too unlikely at its orbit — then it could survive insolations as high as 2.2 times that of Earth. However, this probably isn’t the case. 

3.) If Tau Ceti e somehow beats all the odds and is not only rocky but hasn’t turned into a Super-Venus, one more challenge remains. I mentioned before that there’s a large debris disk in the system. That is bad news for the potential habitability of any Tau Ceti planet, because that disk contains around ten times more asteroids and comets than are in our Solar System. This means that Tau Ceti e, f, and any possible undiscovered habitable zone planet would be frequently struck by space debris, disrupting the peace and stability needed for complex life to evolve. If life did miraculously get a foothold on Tau Ceti e, there’s a good chance it has since been wiped out. 

 

So despite all the hope that the Tau Ceti solar system is something like in Star Trek, I highly doubt that is the case. Is it still interesting and worth continued observations and studies? Absolutely. Is it one of the best potentially habitable nearby systems? Absolutely not. I put my bets on Luyten b or LHS 1140 b having at least some form of life, since both are well within their systems’ habitable zones, orbit very quiet red dwarfs, and are likely rocky (the latter actually is confirmed to be terrestrial).

[KerikBalm]

Generally speaking to the topic title: no, I have no reason to think that is more likely than not. I think there's a small chance that it is... very small.

Its at least 4.3 x the mass of earth, this means it can hold on to a thick atmosphere. At over 4x the mass of earth, it may hold on to helium too (it could be partway between a terrestrial planet and an ice giant).

Its more likely to be a super-Venus than a super-Earth.

On 2/9/2019 at 1:57 PM, ProtoJeb21 said:

So despite all the hope that the Tau Ceti solar system is something like in Star Trek, I highly doubt that is the case. Is it still interesting and worth continued observations and studies? Absolutely. Is it one of the best potentially habitable nearby systems? Absolutely not. I put my bets on Luyten b or LHS 1140 b having at least some form of life, since both are well within their systems’ habitable zones, orbit very quiet red dwarfs, and are likely rocky (the latter actually is confirmed to be terrestrial).

The problem with Red Dwarves is that the habitable zone is so close to them, that all planets in that zone become tidally locked in short order. Without thick atmosphere, you then have a hot side and a cold side. The problem with a cold side is that if the atmosphere is thin enough, it gets very very cold. The atmosphere can then start to liquefy and freeze on the cold side. Then there is even less convection, and more freezing, and the atmosphere collapses. With a thick enough atmosphere, there is enough convection to prevent freezing on the cold side. Venus, for example, doesn't have a cold side in its extremely long nights (it rotates very slowly). So there's then a narrow range of possible atmospheric thickness that lies between "runaway greenhouse" and "atmospheric collapse".

Luyten b, having 3 earth masses, likely held on to a thick atmosphere, and is a venus analogue. Even a 10% increase in the brightness of our sun will lead to loss of hydrogen, and the evaporation of our oceans. The suns brightness increases over time, and we've got about 1 billion years before its too bright. On the other end, there's this: https://en.wikipedia.org/wiki/Faint_young_Sun_paradox

Maybe something special happened to keep Earth warm enough earlier, giving us time to evolve. If life started a billion years later, it may have been too late for something like us.

And then there's the flar activity of red dwarves coupled with the close proximity of the habitable zone. They thought Proxima might have a habitable planet, then they detected a flare from Proxima that would have devestated any life on the planet. Its flare activity was high enough that it was concluded that any atmosphere was stripped away long ago.

Red Dwarves have planets that orbit close, their atmosphere gets pummeled by the solar wind/flares, and has a high escape rate. Once the atmosphere is too thin, it freezes out on the dark side.

I'm quite pessimistic about any reddwarf having a terrestrial planet with water on its surface.

[p1t1o]

Even the most optimistic astro-biologist has to admit that in any given group of planets, life is rare.

Ergo: can only entertain the notion of life if presented with copious signs of it.

[Green Baron]

I don't think so. If i did, it would be irrelevant.

But we may be able to find more (indirect) once a new telescope generation is in service :-)

[Hypercosmic]

I'd say 'no' and give out the points, but ProtoJeb already did that.

Personally, I think if you want an Earth-like-ish habitable extrasolar planet, I'd say Kepler-62f, Kepler-186f, and Kepler-442b (this one could even be a 'superhabitable planet'). Those have their own potential showstoppers, but at least they're not at risk of having their atmosphere fried or going runaway greenhouse like most other so-called 'potentially habitable worlds'. Wouldn't bet too much on vacuum-dwelling, radiation-resistant lifeforms, or supercritical carbon dioxide biochemistry.

Edited February 11, 2019 by Hypercosmic

[Green Baron]

Good point, the faint young sun "paradox", a comfortable system of feedback and circuits that built up and made the earth maintain a surface temp of +/-15°C (which is well above its equilibrium temp.), on a geological scale. Another interesting question is, if there was a global ice age (the earth near its equilibrium temp), how did the earth get out of it ?

But be it as it may, let's see what our solar system has in store for us, before we can get better data about other worlds because imo much is guesswork and speculation.

Edited February 11, 2019 by Green Baron

[KerikBalm]

Well, one explanation of the faint young sun thing, was tidal and radiogenic heating of the Earth.

Quote

The primary mechanism for Earth warming by radiogenic heat is not the direct heating (which contribute less than 0.1% to the total heat input even of early Earth) but rather the establishment of the high geothermal gradient of the crust, resulting in greater out-gassing rate and therefore the higher concentration of greenhouse gases in early Earth atmosphere. Additionally, a hotter deep crust would limit the water absorption by crustal minerals, resulting in a smaller amount of high-albedo land protruding from the early oceans, causing more solar energy to be absorbed.

...

The Moon was much closer to Earth billions of years ago,^[20] and therefore produced considerably more tidal heating.^[21]

Would Earth have been in a permanent snowball state for billions of years if it weren't for the (seemingly uncommon event, based on our solar system, and Earth's moon being huge relative to the planet) event that created our moon?

Its remarkable that our climate has been as stable as it has been (but snowball episodes are worth noting, as well as some evidence that at some points the atmosphere was only about 1/4 the current pressure). Larger stars move through their lifecycle faster. Smaller stars go through it slower, but too small and its a Red Dwarf.

And then you've got to figure old planets have their cores cool, lose magnetic fields, plate tectonics stop, so you need a young-ish star (star and planet being about the same age), that starts already bright enough for the planet, and stays not too bright for billions of years (or something special happening on the planet to stabilize its temperature even as stellar output changes).

And I don't want to hear any Gaea hypothesis about life stabilizign the atmosphere to maintain that... the fossil record shows otherwise. We've got the carboniferous rain forest collapse (plants colonized land, sucked all the CO2 out of the air, caused global cooling, then died off as a result of the climate change), wildly fluctuating O2 levels (from the GOE, to big swings in O2 after that, including periods of very high O2).

Earth's gone from no O2 to over 30% O2, to about 20, from snowball, to ice-less polar caps (nearly the whole mesozoic), etc, all while life has been around

[Green Baron]

4 minutes ago, KerikBalm said:

Well, one explanation of the faint young sun thing, was tidal and radiogenic heating of the Earth.

CO2 concentration is what is mentioned most frequently in papers on the matter.

4 minutes ago, KerikBalm said:

Would Earth have been in a permanent snowball state for billions of years if it weren't for the (seemingly uncommon event, based on our solar system, and Earth's moon being huge relative to the planet) event that created our moon?

Who knows. Probably not. These events are assumed to be connected to the arrangement of continents, snow cover, circulation patterns, moisture in the atmosphere, concentration of elements in sinks and wells. isolation of highly reflective continental mass, shallow oceans ... or, in one word: complicated :-) But earth probably never was totally covered with snow and ice, because of lack of explanation of how to free itself from that state, even taking into account huge flood basalt or other things that change the albedo. We need insolation, without ... red nose :-)

4 minutes ago, KerikBalm said:

Its remarkable that our climate has been as stable as it has been (but snowball episodes are worth noting, as well as some evidence that at some points the atmosphere was only about 1/4 the current pressure).

When was that ?

4 minutes ago, KerikBalm said:

Larger stars move through their lifecycle faster. Smaller stars go through it slower, but too small and its a Red Dwarf.

But otoh red dwarves are stable over a long time (palereddot.org).

4 minutes ago, KerikBalm said:

And then you've got to figure old planets have their cores cool, lose magnetic fields, plate tectonics stop, so you need a young-ish star (star and planet being about the same age), that starts already bright enough for the planet, and stays not too bright for billions of years (or something special happening on the planet to stabilize its temperature even as stellar output changes).

Good point. Earth will reach the state in ~500million years. It is a gradual process, some plates will get stuck in the transition zone between crust and upper mantle. Stabilizing processes like the carbon cycle will stop and that's it with diversity.

4 minutes ago, KerikBalm said:

And I don't want to hear any Gaea hypothesis about life stabilizign the atmosphere to maintain that... the fossil record shows otherwise. We've got the carboniferous rain forest collapse (plants colonized land, sucked all the CO2 out of the air, caused global cooling, then died off as a result of the climate change), wildly fluctuating O2 levels (from the GOE, to big swings in O2 after that, including periods of very high O2).

Not advocating Gaia because not science, but the biosphere (aka life(tm)) has a decisive effect on stabilization, the fossil record is absolutely clear there. The biosphere (besides other sources like tectonics of course) is responsible for the composition of atmo- and hydrosphere and the upper layer on the geology. It offers sinks and wells for C, N, O and others on short- and medium terms. It binds C in warm times and can release it in cold times through activity, just as an example.

It is comlicated. And thrilling :-)

[KerikBalm]

3 minutes ago, Green Baron said:

CO2 concentration is what is mentioned most frequently in papers on the matter.

Yes, which is affected by outgassing, which is affected by the heat gradient, which is affected by radioactive heating... read the quote: "but rather the establishment of the high geothermal gradient of the crust, resulting in greater out-gassing rate and therefore the higher concentration of greenhouse gases in early Earth atmosphere. Additionally, a hotter deep crust would limit the water absorption by crustal minerals, resulting in a smaller amount of high-albedo land protruding from the early oceans, causing more solar energy to be absorbed."

Quote

When was that ?

Supposedly about 2.7 billion years ago... about, from the wiki article on faint young sun

https://faculty.washington.edu/dcatling/Som2016_Earths_Low_Air_Pressure_w_supplemental.pdf

" Our data indicate a surprisingly low surface atmospheric pressure of Patm= 0.23± 0.23 (2σ) bar, and combined with previous studies suggests ∼0.5 bar as an upper limit to late Archaean Patm. The result implies that the thin atmosphere was rich in auxiliary greenhouse gases and that Patm fluctuated over geologic time to a previously unrecognized extent."

Quote

But otoh red dwarves are stable over a long time (palereddot.org).

Yes, but the planet still has to orbit too close, gets tidally locked, experiences a very strong solar wind/great disruption from flares... I find the arguments that they are very bad candidates for life to be convincing.

Quote

but the biosphere (aka life(tm)) has a decisive effect on stabilization, the fossil record is absolutely clear there. The biosphere (besides other sources like tectonics of course) is responsible for the composition of atmo- and hydrosphere and the upper layer on the geology. It offers sinks and wells for C, N, O and others on short- and medium terms. It binds C in warm times and can release it in cold times through activity, just as an example.

It certainly has an effect, and will affect the stable states/equilibirum... but overall, I'm not convinced it makes the climate any more stable. The great oxygenation event was a huge disruption to the climate. The colonization of land had a huge effect.

The only stabilization you get is if life is doing something that makes the environment worse for life... when it does it too much, life starts to die, and it stops making the environment worse for life (a negative feedback loop). It can also participate in positive feedback loops. Like imagine life that is on a world that is a bit too cold, evolves a dark pigment to help warm it up in the day... spreads, the whole planet's albedo warms... life thrives... fine... but that's a positive feedback loop, and those typically have 2 steady states, and a switch can still happen between them. Now suppose there is a bad event, the life starts to die, the planet's albedo increased due to less life increasing the albedo... the life doesn't stabilize this, as more of it dies off, the planet cools further, and snowballs.

Life affects the climate/environment, for sure, but I'm not at all convinced that it will form a system that actively maintains the climate/environment to be suitable for itself.

Look at the GOE, that destroyed the environment for life at that time. It resulted in a massive dieoff, a permenant change in the environment. Life didn't stabilize the environment, it changed it and then adapted to the new one.

17 minutes ago, Green Baron said:

It is comlicated. And thrilling :-)

Oh, for sure. There is so much we don't know because we have just Earth.

I'm a bit of a Rare-Earther, I would love to see another planet that looks well suited for life, or life on Europa/mars, etc... even martian fossils from 2.5-3.5 billion years ago... but we should also look at these planets objectively, and not try to think of a way thhat they could be what we want them to be, but try to make our best guess as to what they actually are.

Earth's history itself is very unclear. Understanding the real story behind the putative snowball episodes, and the solution to the fain early sun paradox, would help a lot in evaluating the prospects that detected exoplanets are suitable for life as we know it or not

[Green Baron]

Yep, that was a Nature paper in 2016, based on a model calculation. But it isn't necessarily real, and somewhat contradictory to other models like https://www.nature.com/articles/s41561-017-0031-2 or https://www.nature.com/articles/nature08955 that suggest biogenic activity to play the biggest role. Don't get me wrong, i am not against the one or the other ! I readily accept outgasing, a much more "mushy" mantle in the early days, methane and CO2 as part of a bundle of reasons for earth's climatic stability over billions of years. And of course a favourable galactic environment ! We can't exclude categorically any of these and it is not a single one source, e.g. primordial heat probably played a bigger role in the past than radiogenic heating. But the amounts and contributions are all debated and nobody can look inside the earth deep enough.

I as well count myself to the "rare earthers" (for now(*)). At least when it comes to explaining the complex interactions that started in the Archaean and have developed further since then. On a high level, one can see evolution is consisting of self regulating processes, but this system is fragile to interruptions and depends on long term stability.

Edit: rare, not raw unique !

 

Edited February 12, 2019 by Green Baron

[KerikBalm]

Well, U238 has a halflife of about 4.5 billion years, so the early earth ad 2x as much as it. For elements with even shorter halflives, early Earth had a loooooot more. At the moment radiogenic heat only replaces about half the heat lost by earth, so primordial heat is still playing a role*.

About 2.1 billion years ago, the U235 concentration was high enough for natural nuclear reactors. We only have the one example, but 4 billion years ago? who knows, there isn't much rock left from back then, its hard to say what role that played.

Early Earth had a lot more primordial heat, a lot more tidal heating, and a lot more radiogenic heating.

I *assume* that the scientists take that into account when discussing this paradox, and that something funky with the sun, or a much stronger greenhouse effect was needed.

Also I'll note that your second link actually argues against biological factors:

First, they disbute that methanogens, for example, were responsible for greenhouse effects:

Quote

It has been inferred that the greenhouse effect of atmospheric CO₂ and/or CH₄ compensated for the lower solar luminosity and dictated an Archaean climate in which liquid water was stable in the hydrosphere^5,6,7,8. Here we demonstrate, however, that the mineralogy of Archaean sediments, particularly the ubiquitous presence of mixed-valence Fe(II–III) oxides (magnetite) in banded iron formations⁹ is inconsistent with such high concentrations of greenhouse gases and the metabolic constraints of extant methanogens.

Then the argue it was actually the lack or paucity of life:

Quote

Prompted by this, and the absence of geologic evidence for very high greenhouse-gas concentrations^10,11,12,13, we hypothesize that a lower albedo on the Earth, owing to considerably less continental area and to the lack of biologically induced cloud condensation nuclei¹⁴, made an important contribution to moderating surface temperature in the Archaean eon. Our model calculations suggest that the lower albedo of the early Earth provided environmental conditions above the freezing point of water, thus alleviating the need for extreme greenhouse-gas concentrations to satisfy the faint early Sun paradox.

Its very complex. Life increases the complexity, but I'm not convinced that it increased the stability. I wouldn't dare argue that it didn't play a large role on the climate and environment, of course.

Of course, Earth would have been all good and hot right after formation, and after the moon formation event, and probably the LHB. But for how long? could life have started fast enough to solve the paradox? I'm thinking no, but I don't know. I'd guess that something abiotic was going on to keep Earth warm enough for life to even start. Also, if the snowball episodes are confirmed, it shows that life didn't stabilize the climate all that well, and it needed to be geologic events to break out of the snowball condition.

* Interestingly, I recently read that Kelvin's calculations on the age of the Earth weren't so wrong because be didn't know about radioactivity, but rather because he didn't consider convection within the Earth. One of his friends used a convection model, and came to about 2 billion years (or am I remembering wrong, and these were modern calculations, and he just wanted to model again with convection), but he didn't push hard because he was friends with Kelvin.

 

[magnemoe]

On 2/9/2019 at 4:06 AM, James Kerman said:

Personally I think we need to thoroughly search our own system, in particular deep sample drilling on Mars, Europa, Ganymede, the ice giants and Enceladus, before looking further afield.  Our tree of life requires liquid water and until there is evidence of it on Tau Ceti e there are far better targets for research in our own backyard.

Life on other worlds will remain a mystery until we have a data set greater than 1.

Looking for oxygen and other signs of life in the atmosphere is easier than an Europa mission, easier to get funding for too since telescopes are multi use. 
 

[Green Baron]

That is a misunderstanding i assume. The assumed lack of biogenically induced cloud nuclei (presented without explanation) does not exclude life. Essentially, the cited BIFs are assumed to be in vast parts the outcome of biological activity. They argue with some reason that a lower albedo due to less continental crust played a bigger role in keeping the temperature low. But, as we know, at the end of the Archaean 70% of today's continental crust (*) had been formed. The processes were much faster, a softer mantle had higher convection rates, etc. I only wanted to present different views on the matter, i am not siding with the one or the other (but accepting all if reasonable).

And so I concede radiogenic heating may have played a role, how big i do not know, but i can imagine that radiogenic heating is less needed for the modeling than other effects, that is probably the difference in our views.

Edit: according to other sources >80% by 2.5Gy (https://www.sciencedirect.com/science/article/pii/S1674987118300501). So i probably can put the paper to the archives of science anyway, the crustal albedo argument is a weak one :-) It so happens sometimes ....

Edited February 12, 2019 by Green Baron

[James Kerman]

27 minutes ago, magnemoe said:

Looking for oxygen and other signs of life in the atmosphere is easier than an Europa mission, easier to get funding for too since telescopes are multi use. 

I agree but in the case of Europa the atmosphere is primarily oxygen caused by charged particles hitting the ice so if you are looking for cyanobacteria or other organisms deep under the surface you would be dealing with a lot of signal noise.  Even evidence of past life on these bodies would answer many questions and raise many more.

[magnemoe]

6 minutes ago, James Kerman said:

I agree but in the case of Europa the atmosphere is primarily oxygen caused by charged particles hitting the ice so if you are looking for cyanobacteria or other organisms deep under the surface you would be dealing with a lot of signal noise.  Even evidence of past life on these bodies would answer many questions and raise many more.

Not talking about the ice moons but exoplanets. Bacteria under the ice will require an landing and an dive. 
 

19 hours ago, Green Baron said:

Good point, the faint young sun "paradox", a comfortable system of feedback and circuits that built up and made the earth maintain a surface temp of +/-15°C (which is well above its equilibrium temp.), on a geological scale. Another interesting question is, if there was a global ice age (the earth near its equilibrium temp), how did the earth get out of it ?

But be it as it may, let's see what our solar system has in store for us, before we can get better data about other worlds because imo much is guesswork and speculation.

As i understand Earth got out of the snowball because it was little who absorbed carbon then the surface was mostly ice so co2 from volcano build up until temperature increased.  
Good chance life created this by removing lots of the co2 in the first part at least the last time it happened. 

[Green Baron]

44 minutes ago, magnemoe said:

As i understand Earth got out of the snowball because it was little who absorbed carbon then the surface was mostly ice so co2 from volcano build up until temperature increased.  
Good chance life created this by removing lots of the co2 in the first part at least the last time it happened. 

The snowball depiction is only hypothetical and the evidence holey. Climate models have their difficulties with it. One would need really high CO2 levels to get out of it by atmospheric heating alone. Widespread glaciation at certain times is undisputed, a totally overfrozen planet is not.