It makes you wonder what created all that CO2 millions of years ago.
From Louisiana State University
LSU researchers find new information about ‘Snowball Earth’ period
It is rather difficult to imagine, but approximately 635 million years ago, ice may have covered a vast portion of our planet in an event called “Snowball Earth.” According to the Snowball Earth hypothesis, the massive ice age that occurred before animal life appeared, when Earth’s landmasses were most likely clustered near the equator, precipitated relatively rapid changes in atmospheric conditions and a subsequent greenhouse heat wave. This particular period of extensive glaciation and subsequent climate changes might have supplied the cataclysmic event that gave rise to modern levels of atmospheric oxygen, paving the way for the rise of animals and the diversification of life during the later Cambrian explosion.
But if ice covered the earth all the way to the tropics during what is known as the Marinoan glaciation, how did the planet spring back from the brink of an ice apocalypse? Huiming Bao, Charles L. Jones Professor in Geology & Geophysics at LSU, might have some of the answers.
Bao and LSU graduate students Bryan Killingsworth and Justin Hayles, together with Chuanming Zhou, a colleague at Chinese Academy of Sciences, had an article published on Feb. 5 in the Proceedings of the National Academy of Sciences, or PNAS, that provides new clues on the duration of what was a significant change in atmospheric conditions following the Marinoan glaciation.
“The story is to put a time limit on how fast our Earth system can recover from a total frozen state,” Bao said. “It is about a unique and rapidly changing post-glacial world, but is also about the incredible resilience of life and life’s remarkable ability to restore a new balance between atmosphere, hydrosphere and biosphere after a global glaciation.”
Bao’s group went about investigating the post-glaciation period of Snowball Earth by looking at unique occurrences of “crystal fans” of a common mineral known as barite (BaSO4), deposited in rocks following the Marinoan glaciation. Out of the three stable isotopes of oxygen, O-16, O-17 and O-18, Bao’s group pays close attention to the relatively scarce isotope O-17. According to Killingsworth, there aren’t many phenomena on earth that can change the normally expected ratio of the scare isotope O-17 to more abundant isotope O-18. However, in sulfate minerals such as barite in rock samples from around 635 million years ago, Bao’s group finds large deviations in the normal ratio of O-17 to O-18 with respect to O-16 isotopes.
“If something unusual happens with the composition of the atmosphere, the oxygen isotope ratios can change,” Killingsworth said. “We see a large deviation in this ratio in minerals deposited around 635 million years ago. This occurred during an extremely odd time in atmospheric history.”
According to Bao’s group, the odd oxygen isotope ratios they find in barite samples from 635 million years ago could have occurred if, following the extensive Snowball Earth glaciation, Earth’s atmosphere had very high levels of carbon dioxide, or CO2. An ultra-high carbon dioxide atmosphere, Killingsworth explains, where CO2 levels match levels of atmospheric oxygen, would grab more O-17 from oxygen. This would cause a depletion of the O-17 isotope in air and subsequently in barite minerals, which incorporate oxygen as they grow. Bao’s group has found worldwide deposits of this O-17 depleted sulfate mineral in rocks dating from the global glaciation event 635 million years ago, indicating an episode of an ultra-high carbon dioxide atmosphere following the Marinoan glaciation.
“Something significant happened in the atmosphere,” Killingsworth said. “This kind of an atmospheric shift in carbon dioxide is not observed during any other period of Earth’s history. And now we have sedimentary rock evidence for how long this ultra-high carbon dioxide period lasted.”
By using available radiometric dates from areas near layers of barite deposits, Bao’s group has been able to come up with an estimate for the duration of what is now called the Marinoan Oxygen-17 Depletion, or MOSD, event. Bao’s group estimates the MOSD duration at 0 – 1 million years.
“This is, so far, really the best estimate we could get from geological records, in line with previous models of how long an ultra-high carbon dioxide event could last before the carbon dioxide in the air would get drawn back into the oceans and sediments,” Killingsworth said.
Normally, carbon dioxide levels in the atmosphere are in balance with levels of carbon dioxide in the ocean. However, if water and air were cut off by a thick layer of ice during Snowball Earth, atmospheric carbon dioxide levels could have increased drastically. In a phenomenon similar to the climate change Earth is witnessing in modern times, high levels of atmospheric carbon dioxide would have created a greenhouse gas warming effect, trapping heat inside the planet’s atmosphere and melting the Marinoan ice. Essentially, the Marinoan glaciation created the potential for extreme changes in atmospheric chemistry that in turn lead to the end of Snowball Earth and the beginning of a new explosion of animal life on Earth.
While previous work by Bao’s group had advanced the interpretation of the strange occurrence of O-17 depleted barite just after the Marinoan glaciation, there was still much uncertainty on the duration of ultra-high CO2 levels after meltdown of Snowball Earth. Bao’s discovery of a field site with many barite layers gave the opportunity to track how oxygen isotope ratios changed through a thickness of sedimentary rock. As the pages in a novel can be thought of as representing time, so layers of sedimentary rock represent geological history. However, these rock “pages” represented an unknown duration of time for the MOSD event. By using characteristic features of the Marinoan rock sequence occurring regionally in South China, Bao’s group linked the barite layer site to other sites in the region that did have precise dates from volcanic ash beds. Bao’s group has succeeded in estimating the duration of the MOSD event, and thus the time it took for Earth to restore “normal” CO2 levels in the atmosphere.
“To some extent, our findings demonstrate that whatever happens to Earth, she will recover, and recover at a rapid pace,” Bao said. “Mother Earth lived and life carried on even in the most devastating situation. The only difference is the life composition afterwards. In other words, whatever humans do to the Earth, life will go on. The only uncertainty is whether humans will still remain part of the life composition.”
Bao says that he had been interested in this most intriguing episode of Earth’s history since Paul Hoffman, Dan Schrag and colleagues revived the Snowball Earth hypothesis in 1998.
“I was a casual ‘non-believer’ of this hypothesis because of the mere improbability of such an Earth state,” Bao said. “There was nothing rational or logic in that belief for me, of course. I remember I even told my job interviewers back in 2000 that one of my future research plans was to prove that the Snowball Earth hypothesis was wrong.”
However, during a winter break in 2006, Bao obtained some unusual data from barite, a sulfate mineral dating from the Snowball Earth period that he received from a colleague in China.
“I started to develop my own method to explore this utterly strange world,” Bao said. “Now, it seems that our LSU group is the one offering the strongest supporting evidence for a ‘Snowball Earth’ back 635 million years ago. I certainly did not see this coming. The finding we published in 2008 demonstrates, again, that new scientific breakthroughs are often brought in by outsiders.”
Bao credits his research ideas, analytical work and pleasure of working on this project to his two graduate students, Killingsworth and Hayles, as well as his long-time Chinese collaborators. Bao brought Killingsworth and Hayles to an interior mountainous region in South China in December 2011, where the group succeeded in finding multiple barite layers in a section of rocks dating to 635 million years ago. This discovery formed a large part of their analysis and subsequent publication in PNAS.
“Nothing can beat the intellectual excitement and satisfaction you get from research in the field and in the laboratory,” Bao said.
Bao’s research is funded by the National Science Foundation and by the Chinese Academy of Sciences.
To read the original article, visit http://www.pnas.org/content/early/2013/02/05/1213154110.1.abstract.
To read more about Huiming Bao’s research, visit http://www.geol.lsu.edu/hbao/.
“””””…..cba says:
March 1, 2013 at 1:35 pm
A snowball Earth could have in excess of 50% albedo with reasonably fresh snow. …..”””””
See the wiki photo of earth covered in ice. You want ice, or you want snow ? I’m not sure you can have both.
You need evaporation to get snow.
In the Arctic and Antarctic, snow comes from moisture evaporated from oceanic waters. Cover those oceans with ice as in wiki photo, and no moisture for snow.
And with no moisture, no clouds, not much to cause water enhancement of CO2 absorption.
Albedo isn’t going to be 50%. Sun illuminates 50+% of earth all the time, and it rotates so most of snowball earth is going to get some daylight sun, which is going to melt the snow surface. (fresh snow, has an excellent anechoic light trapping geometry). As a result, snow reflectance doesn’t stay high for more than a few hours. Melted snow is transparent, and once solar energy enters, it gets trapped by TIR, so reflectance drops way down, close to the 2-3% reflectance of water.
With anything like the earth’s current orbit, and the sun’s current output (say last billion years), an earth without LIQUID oceans, is somewhat untenable. If you don’t have liquid oceans, you don’t get fresh snow; if you don’t have fresh snow, you get melt ice. If you have optical water surface (liquid or solid), you get very low reflectance of solar spectrum energy. You don’t get 50% or higher reflectance.
@Doubting Rich.
“””””…..By the way – what is that about this being revived in 1998? I finished my Earth Sciences degree in 1995 and it was certainly mentioned as a possibility. It was thought unlikely because of the lack of known mechanism to break out of the high-albedo state, but it was accepted that there was strong empirical evidence. My lecturers had respect for empirical evidence, even that contrary to their scientific model……”””””
So picture a snow covered earth (all of it oceans as well) all 90+% scattering “reflectance” your “high albedo state”; how to break out of that (with a degree in Earth Sciences)??
Picture the low relative humidity over snow covered terrains, and the consequent lack of clouds which would contribute to the high albedo state.
Picture an incident TSI of around 1362 W/m^2 and very little atmospheric water vapor to absorb much of that, so a surface irradiance of >1,000 W/m^2 seems more than plausible. With 90% reflectance, only 100 W/m^2 is going to be absorbed by the snow.
Picture the known poor thermal conductivity of snow; its a great insulator; so that 100 W/m^2 absorption is going to be in the surface layers of the snow, and some of it is going to melt and create liquid water, and when the solar blowtorch passes on by, that liquid water will refreeze, and form ice, which is virtually transparent to solar spectrum radiation. That will increase the surface absorption by TIR trapping; and that effect will as they say “snowball”.
Exit stage left high albedo state; enter stage right, low albedo state.
Turn in Earth Sciences Degree shingle
I wonder if Professor Bao (or anyone at LSU) has ever actually seen snow; freshly fallen dry powder snow, or same stuff after the winter sun has shone on it for an hour.
So why the hell would you dig up some rocks to look for Barium Sulphate, just to figure out how snow melts ??
Amazing isn’t it … all that ice at a time Earth’s atmosphere contained enormous amounts of CO2!
And now Earth only has a minuscule amount of CO2 in the atmosphere… and yet it has an ideal warm climate!
Doesn’t that say something about the insanity of the IPCC mantra?
George,
for the 3-4% deep ocean albedo, you’ve got to have that deep ocean visible, either thru clear ice or instead of ice. Fresh powder gets you >50% albedo but as it compacts down into ice, you’ve got something else. You need clear ice to drop dramatically. Maybe you get some nice clear ice/water in melt pools but with nonclear ice below, it will still be higher than deep ocean. Land tends to run between 12-18% albedo – much like Mars or the Moon. Consequently, you’ve got to lose a lot for the snow or packed snow turning to ice to be really bad. Ultimately, it is going to lose out to the sunshine, especially as it gets more compacted and dirtier. Those melt ponds may well not remain melted over night as the lower RH is going to give some evaporative cooling even with T above freezing and it likely will take a while for that. The average power is still going to be around 341w/m^2 and there is an awful lot of ice in 1 square meter when there is 1 or 2 km of thickness.
“””””…..cba says:
March 4, 2013 at 5:47 pm
George,
for the 3-4% deep ocean albedo, you’ve got to have that deep ocean visible, either thru clear ice or instead of ice…..”””””
Well I’ve looked into the deep ocean through nothing at all (stuck my head down in it) and I can assure you that it isn’t visible at all. If you have a lot of phytoplankton, then you get some back reflectance, but without it you see blackness.
Now The infra-red Handbook gives bulk reflectance data for various phytoplankton conditions, and in no case does it give a reflectance exceeding 8% and that enhanced reflectance over the normal Fresnel reflectance exists only for the spectral range from 0.5 to 0.6 microns wavelength. For the shorter wavelength range 0.4 to 0.5 microns, the bulk reflectance is higher at lower plankton densities, but never exceeds 5%. And of course there is a lot less solar energy below the spectral peak, so even 5% reflectance reflects not much energy. Refrozen melted ice only needs facets of a few microns size to refract solar rays into it, instead of scattering them, and once inside the water and particularly with scattering centers in the water, the radiation becomes diffuse, and
much of it is trapped by TIR (Total Internal Reflection).
The human eye is a very poor judge of reflectance of solar energy. The very best off the shelf antireflectance filter you can buy (for camera lens protection) has less than 0.3% reflectance over the visible range. The reflected solar disk seen off that filter is still far to bright to be viewed by the naked eye; you would swear the image is half as bright as the direct sun view, yet it is only 0.3%. And you can check that low reflectance yourself, by reflecting the solar disk onto a shadowed surface, and comparing it to an ordinary piece of window glass or even some high priced brand AR filters, that claim to be low reflectance (they aren’t)..
The point is that the high Lambertian scattering of fresh dry snow, gives a high reflectance in the sun, for only a few minutes that it takes to melt the surface crystals, that refreeze into glassy facets. The eye thinks it looks brighter, but it is getting fooled by the specular reflection of the solar disk that comes off randomly oriented facets, into ther eye.
And once there is absorption in the icy snow, then simple heating creates a continuous melting process, that just accelerates. Yes it will refreeze when the sun goes by but it will never again be high albedo.
And where do you get this 341 w/m^2 number from. The TSI is 1362 W/m^2; that is an AREAL POWER DENSITY figure, the RATE at which solar energy is delivered to the surface (don’t forget the typical attenuation to around 1,000 W/m^2).
342 W/m^2 probably can’t melt the snow, but 1,000 W/m^2 can. Power and power density, is an instantaneous quantity; you do NOT average power numbers. One 20 kton bomb on San Francisco every 25 or 50 years, really is not very much average power. Try convincing the citizens that it won’t do very much damage (on average). The spots on earth that are in daylight receive about 1,000 W/m^2 (normal to the sun vector); whenever they are in daylight . The spots that are not in daylight receive basically zero, all the time they are not in daylight. They particularly do not receive 341 W/m^2 when they are not in daylight.
George,
The 341 is an average. Remember that not just night and day but 1362 (or more like 1000 w/m^2) is occurring only when the Sun is very high overhead. Other than local noon directly at where the Sun is directly overhead, you start to suffer from the trig angles and thicker atmosphere. Remember too that scattering intensifies at the 180 deg. reverse direction. And again, my point was that while clear ice approaches that of deep water in albedo, even old snow has significant albedo compared to most of Earth’s surface. The fact that Earth has about 0.3 albedo is due to clouds and atmospheric scattering when there is no massive glaciation. Otherwise it would be somewhat less than Moon or Mars due to the vast oceans. While fresh snow doesn’t last long, not so fresh snow is still going to be higher albedo than land surface averages. Also, the simple concept is that today’s Earth reflects about 30% of incoming (albedo) and the atmosphere traps about 30-40% of the outgoing surface radiation. Averages turn out that Earth is warmed by around 239 w/m^2 of incoming which is balanced by about 239 W/m^2 radiated mostly from the surface which makes it through the atmosphere and clouds. Of the difference in what is radiated from the surface and what makes it out the atmosphere, about 1/3 is due to clouds and 2/3 to ghgs, primarily h2o vapor. If much of the h2o vapor goes away along with the clouds, it will require less surface T to balance the incoming. Note that the h2o is like co2 in that a doubling or halving has a relatively little effect so a serious decrease in absolute humidity is going to have a fairly small change – somewhere around 2-3 times that of a co2 change. Co2 halving is close to around 10% of the total co2 contribution. If we assume a simple albedo of around 30% for this glaciated world without clouds and with fairly low h2o vapor, our average temperature needed for balance would still be very close to 0 deg C. Any albedo above 0.3 would essentially drop the average to below 0 as would any serious drop in absolute humidity. Even current conditions have our average only about 15 deg C.
[Paragraphs are your friends. 8<) Mod]
“””””…..cba says:
March 5, 2013 at 1:19 pm
George,
The 341 is an average……”””””
Power is a rate of doing work, or a rate of using energy, or a rate of transport of energy; it is a differential quantity with an instantaneous value. I think I just said you cannot average power or power density. Average power is a meaningless concept; on average NOTHING is happening.
And I beg to differ on when and where the sun delivers 1362 W/m^2 to the earth (of which about 1,000 makes it to the surface) assuming about air mass 1.5 which is the usual assumption from which available solar energy calculations are commonly done. You also missed that bit about the area normal to the sun vector. You still get 1362 W/m^2 normal to the sun vector, no matter where the sun is (presumably above the horizon).
Yes the air mass absorption and scattering reduces what you get at low sun angles, but the TSI is still 1362 W/m^2 even at the north pole during daylight hours; but air mass numbers are higher so the 1,000 W/m^2 at the surface comes in a bit lower. The whole point of steerable solar collector arrays, is to point the array normal at the sun, wherever it is.
And the problem is that most of earth’s albedo is a consequence of clouds; NOT snow and ice.
Albedo is NOT a reflection coefficient, it is the fraction of solar spectrum EM radiation arriving at the earth, which is redirected away from the earth as solar spectrum EM energy, unmodified. Processes which change the wavelength of solar spectrum energy are not contributors to albedo.
If it doesn’t escape from earth capture, as solar spectrum radiation without inelastic processing; it isn’t a part of albedo.
The “reflectance” of fresh snow can be very high; but if that snow is on top of Antarctic land or Arctic ice, well there isn’t much solar spectrum energy there to reflect, so the contribution to albedo is miniscule.
And we do know that there isn’t much solar spectrum energy in the Arctic or the Antarctic; it is conjectured that may be the reason it is so cold there, so that you get all that ice and snow sitting around.
The ice and snow, do not make it cold in the polar regions; it is the cold in the polar regions that makes the icea and snow.
Cooling of the earth takes place during the post noon hours in the hot tropcal deserts, where the cooling rate is more than ten times what it is in the polar night times.
They tell us that the earth BB equilibrum Temperature is about 255K. At that Temperature 341W/m^2 isn’t going to melt anything; but 1362 W/m^2 surely will.
I somehow don’t think you could sell me a hi fi stereo sound system. A typical symphony orchestra covers about a 96dB dynamic range during a concert (the ones I might attend anyway), and if you average out the power output of the orchestra and feed that to the audience; they waill all fall asleep.
“Average power” and “RMS power” are nonsense gimmic terms invented by shyster audio sales people. Power is power; instantaneous power, is what knocks your socks off at a French organ recital.
George,
Pretty much everything has an average. Temperature itself is an average. TSI at the N pole may be 1362w/m^2 for a lambertian disk but that lower angle of incidence means the actual number of m^2 getting that 1362 W is going to be more, making the average less. Also, at low angles of incidence such as one experiences at higher latitudes, even water loses that low reflectivity and starts providing some serious reflections (glare). Ice is going to radiate with its characteristic BB curve too. Its LWIR peak is not limited by SWIR or visible reflectivity which would lower the emissivity.
I’ve never stated the current ‘cryosphere’ played much of a role in today’s albedo. It is only where there is minimal solar incoming and even water would provide a relatively high reflectivity at the lower angles of incidence. I am a firm believer in the IRIS effect. I don’t know if LIndzen is right about cloud reflectivity variation (due to different nucleation particles) or if it is more the simple crude concept of more cloud cover vs less cloud cover but we have a setpoint control system for temperature. When glaciation occurs, we have a short circuiting of this mechanism as the high surface albedo replaces the cloud albedo so things get stuck on cold until such times as things warm up enough again.
That 255k is based upon the simple average of 239 W/m^2 is coming in so there must be that average going out for there not to be a loss or accumulation of heat energy and hence a necessary change in temperature. The reason why our average surface T is around 288K is that in order for earth to radiate that much (239W/m^2) the surface must radiate another 150 W/m^2 due to the trapping or blocking of the atmosphere of close to 40% of what is radiated. Change the albedo value from 0.3 and you’ve got a seriously different amount of absorbed incoming power than 239 W/m^2 so there’s big difference in what the surface T needs to be. Also, if the snowball scenario takes place, you’ve got major differences in what will be trapped – especially if there’s no clouds and very little h2o vapor.
BTW, that 90dB of orchestral variation when combined in a typical auditorium with 30db average noise is going to put you at 120db which is the threshold of pain. It’s also an acoustic power density of 1W/m^2. Considering that sharp noises are more damaging to hearing than continuous noises and that long term damage can begin well below 120dB, it would be problematic for that wide of a dynamic range unless you have important sounds going on that are less than the room noise. A question I sometimes give students is if one is producing 100 W of acoustical power, under perfect conditions and assuming the inverse square law is in effect, how far away could someone theoretically hear it?
A paper I read from Octave Levenspiel, T J Fitzgerald, and Donald Pettit was interesting; it proposed a much elevated air pressure ~4-5 bar of carbon d. I doubt it is religiously driven and suspect it is scientifically based. I particularly like the idea of our sister planet’s atmosphere being a model for our own.
Indeed, did not the strange differences in planets first strike the scientific researchers when our tech allowed us to speculated as to why the differences?