A fifth of Earth’s geologic history might have vanished because of glaciers

https://www.nationalgeographic.com/science/2018/12/part-earths-crust-went-missing-glaciers-may-be-why-geology/

by gricardo99 • 8 years ago

183 62 8 years ago

nationalgeographic.com

captainperl• 8 years ago

One of the most interesting geology articles I've ever read.

stareatgoats4• 8 years ago

Kudos to real scientists who bit by bit uncovers what happened in earths past, in ever-increasing resolution.

Whether "snowball earth" is accurate or not, what appears in outline is an earth that would have been uninhabitable for humans under most of, and even in relative recent, geological history.

It begs the question of how we might deal with the situation where the globe once again becomes uninhabitable (if we survive that long): terraforming or cocooning. The latter seems the best bet.

craigsmansion• 8 years ago

Or maybe even more tantalising, how did the previous sentient species deal with it. Or to reverse that question, is there something a hypothetical species, akin to our own, could have constructed that could have withstood Snowball Earth ? :)

It sounds easy enough, objects in space, large structures, unnatural concentrations of radioactive materials, sure, but over millions of years with kilometers of the top crust simply shaved off and recycled through the core of the planet?

It's amusing our notion of "glacial" loses meaning over such time-spans. How can it do anything, since glaciers just lie there. But over millions of years, it's a high-speed efficient grinding machine the size of a planet.

Conversely, as to how we might deal with the situation, ludicrous though it might seem with our advances and technology, maybe we simply can't. Even a passive beacon on the moon which wouldn't have suffered from Snowball Moon; it seems plausible enough, but it has to withstand at least 250 million years of the moon's night/day cycles. Is there something we could build right now that could withstand that?

Maybe? Probably? But for now I'm content the Snowball Earth hypothesis spices up a lot of Lovecraft stories. "And with strange aeons even death may die” indeed.

avereveard• 8 years ago

Even things on dead planet like the moon can't survive indefinitely because meteors either striking it or dusting it, even if we etched the moon with nuclear blasts contour would get fuzzy and disappear over million years.

One option would be to put in one Lagrange point some high quantity of radioactive material. You'd need to pick quantity and material well tho, because material with short hair life would cool off to get and become just a rock and materials with too long half life would be very hard to detect due their low emissions.

Give it a shape nature would have had time to replicate like an empty cylinder and it would likely be the best way to leave artifact for million years into the future. Won't be able to store any meaningful information beyond "someone was here" and future people coming to bertrand teapot style of argumentation against God would have a hell of a shock upon rediscovery

stareatgoats4• 8 years ago

how did the previous sentient species deal with it

I like your thinking :-) It's the kind of fantasizing that I'm convinced is at the core of human progress, based on hardly more than a number of currently unknowable "what if"s.

It is, as you point out difficult to know if such a species could have existed. But if they did and if they tried to survive, we might be fairly certain that they failed barring something even more fantastical, currently only to be found in the darkest corners of youtube.

The real utility of this line of thought is IMO how we might try to survive the same conditions, since there is no real assurance that it could never happen again. We don't have the answer yet, agree.

maxerickson• 8 years ago

A big lump of Uranium-236 would probably survive that long.

jerf• 8 years ago

At the time scale of billions of years, the question of whether there was sentient life on Earth is roughly equivalent to asking if there is sentient life on other planets, since Earth is very nearly (but not quite) another planet at that time scale. If sentient life arose that quickly that means it is even easier than we thought it was to arise, by quite a bit. The fact we don't see any in the sky would strongly suggest (but not prove) to me that there was not a previous civilization. (The most parsimonious explanation as to why there aren't a lot of civilizations in the sky is that for yet fuzzily-understood reasons, they can't arise much more quickly. [1])

Plus, while the narrative that "evolution increases the complexity over time" isn't as strong as some may suppose, it does provide a ceiling to complexity over time, and I'd say most of the evidence that we have would strongly suggest that there isn't any feasible way that the biology of a billion years ago could have supported intelligent life, because that ceiling is just too low. Today, there seems to be several possible feasible lines for intelligent life (birds, sea mammals, octopus) in the "short-term" multi-million-year future, with homonids getting there first, but a billion years ago I don't think that was the case. I suspect your average ant nowadays is more intelligent that much of what was around back then.

Oh, and, yes, we could build something that would survive on the moon. In particular, we're not obligated to put only one thing on the moon; that's an artifact in thinking with the exact precise technology of today, where's it's really expensive. In another 50-100 years it's quite plausible that putting up such a momument would be considered on the scale of an ambitious art project, and it's not hard to imagine dozens and hundreds of such monuments being put on the moon over time. Local materials can be used for bulk, and the only upper limit on the size of such a momument would be the energy available for whatever it is you wanted to do with it. Moving around local materials and building the equivalent of a pyramid would be almost feasible today ("almost" here being "less than a factor of magnitude of development away"), for instance, and melting & refreezing mass quantities of lunar surface for some visually-obvious effect is eminently practical if you have fusion. (And if you have fusion that can use the He3 on the moon, downright cheap.) It's not hard to conceive of monuments miles in size, or if you assume self-repairing or -replicating machinery, you can make something visible from Earth feasibly. Even with only solar power, that just slows the project down. Had that been done billions of years ago, some of them (or some of it) may have been destroyed by meteors but the vast majority would still be there. In another 100-200 years of reasonably-projected technological advance we'd be able to consider completely resculpting the effective appearance of the surface of the moon, for any number of reasons and in any number of ways. The moon shows no evidence of this, which would be enough to say that if there is a sentient civilization in Earth's past, it would put the Great Filter back in front of us again. (Albeit much more weakly, since only one civilization may have died before resculpting the moon.)

It's still faintly possible that we'll explore the moon in more depth that we have today and find "something" interesting. The fact that it's soooo untouched at a bulk scale suggests to me it's not likely, but it's possible some civilization got to where we are today, +/-50 years, and then died back, leaving just a trace on the moon, just as we have so far.

(IMHO, the most recent paper on the Fermi paradox from a couple of months ago puts the Great Filter behind us fairly firmly, by showing there's no compelling reason to assume the sky should be full of civilizations.)

[1]: It is well-understood that you need at least some time for complex elements to develop, and in enough quantity to form useful planets and such, so you do need at least some time for some stellar generations, but there is no currently-known reason that I'm aware of that the sky should not be inhabited by a multi-billion-year old civilization. On a cosmic scale, Earth isn't that late to the party in some sense, but looking at its history it still seems like you could shave some billions of years off of its history and still get an "Earth-like planet" somewhere else.

meroes• 8 years ago

The society would have to have never discovered radioactivity to go undetected this long. In comparison it will take millions of years to wipe out human traces ever since the first atomic testing was done.

thaumaturgy• 8 years ago

You would probably find this article interesting: https://www.theatlantic.com/science/archive/2018/04/are-we-e...

It starts out as a hypothetical between a couple of researchers that resulted in a paper on the longest-lasting effects of human civilizations.

It's a good read, but the summary is that human civilization has resulted in atmospheric changes which will be detectable 100 million years from now, and we've got that much atmospheric evidence buried in geology without similar evidence for a past civilization.

hirundo• 8 years ago

Could an advanced species / civilization have risen and fallen during this period, leaving no trace?

stestagg3• 8 years ago

What if, by unbalancing the worlds ecology, said civilisation triggered that ice-age?

stareatgoats4• 8 years ago

What evidence do you have that there is some such thing as a "balanced world ecology" at all? It seems to me that all the evidence, in addition to logic, is in the opposite direction.

garmaine2• 8 years ago

Then the survivors would have lived relatively comfortably in smaller populations in habitats on the equatorial sea ice.

But it is hard to imagine a culture having sufficient technological capability to cause climate change without also achieving space flight.

Moot point though because the pre-Cambrian fossil record lacks anything that could have evolved into intelligent life so quickly.

nurettin2• 8 years ago

Sure, but why would they also not leave any trace on the moon?

ajmurmann2• 8 years ago

All we have left is a flag and some comparatively tiny equipment. If they had left the same would we have found it yet?

hoorayimhelping2• 8 years ago

Snowball Earth theory says entire earth was covered in an ice sheet dozens of miles high. There might have been a ring around the equator of unfrozen water or slush.

It seems very hard for life to survive under those conditions, let alone complex life, let alone advanced life / civilizations.

daveFNbuck• 8 years ago

The article also mentions that the ice scraped away 1.9 to 3.1 miles of crust, so this period includes a lot of time before snowball Earth.

Paradigma11• 8 years ago

I have read that we would see different mineral and metal deposits due to mining activities of an advanced civilisation.

jl6• 8 years ago

Wow, I always assumed that complex life prior to our own was unlikely because it would have left a trace that we could detect. But if there is a plausible mechanism by which all such traces would have been erased, then who knows what might have happened deep in those billions of years when supposedly only single-celled life existed?

Perhaps Earth’s previous inhabitants triggered runaway global cooling, effectively hitting the reset switch back to single-celled life. Perhaps they escaped to Venus and vowed not to let the same thing happen there, but got it wrong in the other direction.

erikpukinskis7• 8 years ago

Even on shorter timescales, there are 100+ ton milled monoliths all over the world, which are seemingly 4000+ years years old. Yet the civilizations of 4000 years ago don’t seem to have known how to mill such stones. It probably wasn’t until the 19th century at the earliest that we “re-learned” the basic skills required.

My default assumption is that history has only picked up, at best, the latter cycles on big time scales.

zilian• 8 years ago

Do you have sources for those claims ?

a3n• 8 years ago

Maybe. But the political/industrial class would have mind-fucked us into clamoring to do nothing about it. If they went to Venus, only the people who could afford or command it would have made it, and they would have died off almost immediately because they had no minions to hold up the bottom layers of civilization.

rjf723• 8 years ago

I'd be hesitant to attribute any sort of hypothetical causes, but it's fun to also consider such scenarios when thinking just one rock a bit further out. Mars was at one time a warm, watery planet not dissimilar to Earth. It's going to be extremely interesting once we get feet on the ground and can start really digging into the planet's past, quite literally. Most tantalizing of course is that it seems to have had all that was necessary to see the development of life. In many ways even finding absolutely no evidence of life at all will be as exciting as finding the opposite. Okay definitely not as exciting, but it'd certainly be really quite interesting!

aerophilic• 8 years ago

I find the use of zircons in this context very interesting. Starting with the Wikipedia article: https://en.m.wikipedia.org/wiki/Zircon

I went down the rabbit hole and learned a bit about Geochronology: https://en.m.wikipedia.org/wiki/Geochronology

It is interesting how they “break up” dating depending on the time frame, for example some dating is only measured by “eon” (half a billion years), whereas the “finest” measurement seems to be “age” which corresponds to single digit millions of years.

A bit humbling to think that all of humanity can “fit” in the smallest geological measure of time.

cbkeller4• 8 years ago

Yeah, I think the vastness of geologic time has been aptly described as "geology’s signal contribution to human thought" -- the same way astronomy showed us we weren't the literal center of the universe. I think about Myr and Gyr timescales every day at work, but it's still hard to really intuitively grasp.

Obligatory John McPhee:

Numbers do not seem to work well with regard to deep time. Any number above a couple of thousand years—fifty thousand, fifty million—will with nearly equal effect awe the imagination.
Consider the earth’s history as the old measure of the English yard, the distance from the king’s nose to the tip of his outstretched hand. One stroke of a nail file on his middle finger erases human history.

hoorayimhelping2• 8 years ago

So does this imply that we'll never know if the Cambrian Explosion is actually an explosion or just a continuation from a previously unrecoverable geological record? Is it even possible to have complex multicellular life under snowball earth conditions?

Although it’s likely down to a number of factors, one possibility is that Snowball Earth’s erosion was so significant that there wasn’t much topography left to erode when all was said and done. The planet simply needed to forge more land first, and that takes time.

The balance of earth is so interesting. The process that forges new land (volcanism) is the same process that beats back snowball earth and re-balances the atmosphere with more CO2.

It's a bit old and cheesy, some of the info might be outdated, but this is a great episode on this topic: https://www.youtube.com/watch?v=XEiu611KsUo

mannykannot• 8 years ago

The process that forges new land (volcanism) is the same process that beats back snowball earth and re-balances the atmosphere with more CO2.

And I believe volcanism, at least the sort that is most common today (that from ocean-margin subduction zones, rather than that from spreading zones like Iceland or hotspots like Hawaii) results from subducted sediments melting into magma, with their melting points reduced by the presence of subducted water. If so, then do we have the large amounts of sediment, created by the snowball-earth glaciation, setting the stage for the volcanism that ends it?

There are fossils of Precambrian, post-snowball multi-cellular life, but they are not very much like, and nowhere near as diverse, as what appeared in the Cambrian, so I think the explosion still looks like a real event and not just an artifact of an imperfect record.

http://www.ucmp.berkeley.edu/vendian/ediacaran.php

hedora• 8 years ago

Ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn! [0]

Since the erased part of the geological record starts 100’s of millions of years before the climate event that froze everything, do we even know that some earlier civilization didn’t force the climate off balance with e.g. greenhouse gasses, which ended up obliterating all multicellular organisms, and wiping the geological evidence?

Other recent news about ocean current disruptions, and methane melting feedback loops in the artic suggest we might be headed that way too...

[0] https://en.m.wikipedia.org/wiki/R%27lyeh

robocat• 8 years ago

From another answer: “the most advanced multicellular organism I've seen anyone propose prior to the last snowball is still only a sort of sponge”

cbkeller4• 8 years ago

So does this imply that we'll never know if the Cambrian Explosion is actually an explosion or just a continuation from a previously unrecoverable geological record? Is it even possible to have complex multicellular life under snowball earth conditions?

That's a good question. I'm the first author of the new PNAS article discussed here (open access at https://doi.org/10.1073/pnas.1804350116). This does raise some questions about preservation bias and taphonomy, but there are areas we know escaped Neoproterozoic erosion (mostly at actively rifting continental margins) and we can find continuous sedimentary sections from the Cryogenian to the Cambrian -- and in these sections we still see a pretty rapid rise in complex shelly fossils in the early Cambrian. That said, when people first started talking about the "Cambrian Explosion", we didn't know much anything about the Ediacaran biota [1], the Ediacaran extension of the "Small Shelly Fauna" [2], or the Doushantuo Formation [3] -- so the evolutionary problem's not quite as bad as when Darwin first worried about it.

One new point to add is that erosion and comminution of this much crust may be expected to free up a lot of phosphorus stored in the igneous crust -- arguably the key limiting nutrient on geological timescales. This seems to be be consistent with previous observations of an increase in phosphorus abundance in sediments around Cryogenian times [4].

[1] https://en.wikipedia.org/wiki/Ediacaran_biota

[2] https://en.wikipedia.org/wiki/Small_shelly_fauna

[3] https://en.wikipedia.org/wiki/Doushantuo_Formation

[4] https://www.nature.com/articles/nature20772

cbkeller4• 8 years ago

Oh, and regarding the survival of life through a Snowball Earth state, there's been some interesting discussion of potential refugia such as polynyas [1] and cryoconite ponds [2,3], though for context the most advanced multicellular organism I've seen anyone propose prior to the last snowball is still only a sort of sponge [4]

[1] https://en.wikipedia.org/wiki/Polynya

[2] https://en.wikipedia.org/wiki/Cryoconite

[3] https://onlinelibrary.wiley.com/doi/abs/10.1111/gbi.12191

[4] https://www.nature.com/articles/ngeo934

edmundsauto• 8 years ago

I find this stuff just absolutely fascinating, but have trouble finding reputable documentaries on the subject. YouTube is filled with "History" channel crap, and it's so disappointing to get all excited to learn, then be shown the crap they push out.

So, while apologizing for hijacking with an OT comment, do you have any docs you can recommend on the topic of geologic formation/periods of the Earth?

Balgair• 8 years ago

Likely there were a few 'explosive' events near the time of the Cambrian explosion. The Avalon Explosion [0,1] was about 33 million years earlier than the Cambrian Explosion. I would bet that our understanding of Life's history on Earth, and in the solar system in general, is only at the very beginning. Likely, our descendants will be looking at this understanding just like we look back at old 1890's paleontologists and their laughable Dinosaur models.

As an aside: I think that ML and RNNs would be a great tool for paleontologists to use for fossil hunting. Not just for automated drones scanning the lonelier places on Earth, but just to identify potentially 'rich' areas in the first place. Via petroleum studies, we know a fair bit about the Earth and the layers of sediment under it. Using that data, I think it may be possible to help narrow down the areas where good fossilization may have occurred and then send the armies of grad students out to those places, helping increase the percentages for finds.

[0] https://www.youtube.com/watch?v=Jpi2VJj5PhY

[1] https://en.wikipedia.org/wiki/Avalon_explosion

ajmurmann2• 8 years ago

It's interesting how most comments here immediately see this gap in our history book of Earth as a potential time span during which another advanced civilization could have developed and gone extinct (my mind did the same). Meanwhile the article without much discussion jumps to this: "complex life first emerged when Snowball Earth’s monstrous mealtime came to an end."

lostmsu• 8 years ago

TL;DR; Earth appears to have been covered by miles deep ice for many hundred millions of years during the last billion, and that caused normal geological leftovers of the period to be nonexistent. The best info for that period is stuff frozen into zircon crystals, which scientists think supports the ice hypothesis.

A fifth of Earth’s geologic history might have vanished because of glaciers

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