
A fifth of Earth’s geologic history might have vanished because of glaciers - gricardo99
https://www.nationalgeographic.com/science/2018/12/part-earths-crust-went-missing-glaciers-may-be-why-geology/
======
hoorayimhelping
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It's a bit old and cheesy, some of the info might be outdated, but this is a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](https://www.youtube.com/watch?v=XEiu611KsUo)

~~~
cbkeller
> _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](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](https://en.wikipedia.org/wiki/Ediacaran_biota)

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

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

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

~~~
edmundsauto
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?

~~~
cbkeller
NOVA's always been my favorite science documentary series. I don't know if
they've ever covered snowball earth, but they have a somewhat recent series on
geological history of North America:
[https://www.pbs.org/wgbh/nova/series/making-north-
america/](https://www.pbs.org/wgbh/nova/series/making-north-america/)

------
stareatgoats
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
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.

~~~
meroes
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.

~~~
sgt101
Billions for sure - we know because the natural reactor at Oklo 1.7 billion
years ago is still very much detected.

[https://en.wikipedia.org/wiki/Natural_nuclear_fission_reacto...](https://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor)

~~~
Ericson2314
Very cool. Glad to learn about that!

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

~~~
cbkeller
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._

------
jl6
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.

~~~
erikpukinskis
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
Do you have sources for those claims ?

~~~
erikpukinskis
I just watch a lot of Brian Foerster videos on YouTube e.g.
[https://youtu.be/AGBOf8mrWjs](https://youtu.be/AGBOf8mrWjs)

Baalbek is a good place to see 1000+ ton milled stones: [https://youtu.be/jo-
oEk8itlo](https://youtu.be/jo-oEk8itlo)

Cuzco also seems to have some pre-Inca constructions that can’t be explained:
[https://youtu.be/66x9VLwZaDQ](https://youtu.be/66x9VLwZaDQ)

------
ajmurmann
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."

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

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

~~~
stareatgoats
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.

~~~
erikpukinskis
I guess I share your problem, I’m not sure “balanced” is the right word. You
could have two species, a single celled animal and a single celled plant and
ostensibly that would be “balance”.

Maybe a better word for what is at risk is “diversity”. At this time there are
still wild ecologies with incredible diversity in all three phases of water on
Earth, the frozen, the liquid, and the steamy.

And there are also partly dead places. The American Midwest is largely
ecologically dead, although we know before the European settlers came there
was stable soil and incredible biodiversity there.

But balance and biodiversity are connected. In a diverse ecology, you can
remove any species, or turn any dial slightly, metabolism will dip, and then
roar back into full power because there is so much latent genetic material in
the ecology ready to go.

That’s been destroyed in a place like the Midwest. If you stop putting oil
into that ecology, the metabolism would plummet, and it would take a million
years to return to anything close to what it was before European settlers.

In a so-called “balanced” ecology, metabolism would rebound on a scale of
decades or even seasons.

The moral assumption underlying this is that the most metabolism per square
foot of solar energy is the most good.

~~~
stareatgoats
Ok, I think we are talking about two different things:

One thing is biodiversity and the ecological resilience of biodiverse systems,
of which there are many (still) where different species live in a healthy,
productive and dynamic balance. These habitats are under attack for sure,
spurred by industrial production modes of various kinds.

Quite another thing is the notion (represented by GP if I'm correct) that the
whole earth somehow is a balanced system, were it not for greedy humans. This
is a mystical belief that I don't see any proof of.

It is far-fetched not to think that comet impacts, massive volcano eruptions
and/or solar radiation variance accidentally could make most if not all
ecological systems devoid of life, quite without human intervention.

~~~
stestagg
tl;dr, It was a light-hearted ironic idea, not some statement on the impending
downfall of human civilization

"that the whole earth somehow is a balanced system, were it not for greedy
humans"

This was in no way implied by what I said!

I think the word balance is justified here, the word I got wrong was ecology
(I meant climate, but it was late, and I didn’t expect such a defensive
response to my joke,…).

Either way, both the climate and ecology of earth work by _balancing_
conflicting interests and drivers. food chains, carbon cycles, etc.. all are
based on interlocking processes that combine to create a system that is stable
at a macro level (Of course localized factors can make things seem much less
stable). But on the whole, these systems are balanced. Things periodically
come along and upset that balance, and it takes a while for the system to
adjust and re-balance, typically with a result that is different from before.

My point was that it would be ironic if ANY civilisation got to the level
where it could alter these systems meaningfully, but by doing so, and not
understanding what/how they were doing things, created a situation where not
only were they wiped-out, but also all trace of their technology was wiped-out
too.

I accept that this exact scenario is extremely unlikely, as our current models
predict that in these situations, at least some of the population would
survive due to those localized factors, but the civilisation could easily be
destroyed by sudden and climactic shifts.

It's unclear (to the best of my knowledge) if we would expect the historical
record of such a thing to be carried by these people, but a lot of the detail
of our knowledge of roman and pre-roman times(1,000s years, not millions) has
been derived from archeological records, so it's not unreasonable to assume
that if Ice were to scour all hard evidence of such things from the surface of
the earth, then the knowledge of such may die out or become so garbled that it
ceases to be believed.

Of course there /are/ parallels with the situation modern humans find
ourselves in. I think there's little doubt that what we do has an effect on
the balance of the world's climate and ecological systems (you eat a chicken,
that has affected the food chain by an infinitesimal amount), but how much
impact we will have, and our ability to comfortable adapt to any resulting
changes would require a much longer response, and isn’t relevant to my
original post at all :)

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

------
lostmsu
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.

