A lot of descriptive geology is just pattern recognition. I spend a lot of time Googling pictures of various structures, minerals, and other phenomena to get an idea of how the same thing can look wildly different.
So today:
….no, Google. No.
(Psst: This is nodular bedding.)
Andrew asked:
Given ancient alien artifacts which take the form of giant stone cubes, made roughly fifteen million years ago, on an airless moon, what sort of information about them or their makers could a geologist infer from analyzing them?
All right, off the top of my head:
Age analysis:
Why do we care how old the rock is? Well, if it’s a wildly different age from what it’s sitting on, that implies some interesting things. As does knowing how long it’s been sitting out on the surface, since those two numbers might be quite different.
Basic compositional analysis (here I’m assuming igneous or metamorphic rather than sedimentary rocks):
Visual assessment:
Just by looking at it even, there will be clues about how these things were–or weren’t–made. Tool marks? No tool marks? Or if you look microscopically using some sort of pocket scanning electron microscope, what will you see? Crystals cut cleanly in half? Evidence of flash melting, as if these were shaped using some kind of super heated plasma blade? Or were they made in molds, in which case everything would have crystallized perfectly flat against the mold surface? These visual clues might tell you the most about the makers of the artifacts.
This is obviously a non-exhaustive list. I’m sure there’s a million other things a geologist with a different specialization than mine could think to assess. But hopefully this will get you started!
In perfect Rachael World (you know, the same place where my best friend Kat will be Minister In Charge of Hot Forking People Wot Deserve It) everyone will be required to take a basic geology class. And not be allowed to escape until they have at least a rudimentary grasp of the concept of Deep Time. (That thing that involved metaphors about if the life of the Earth was a football field, humanity’s entire existence would be the last blade of grass, etc.) Once you’ve had your mind completely blown by the immensity and longevity of the universe, you end up with two contradictory but true conclusions:
Make it count.
Given a rough Earth analog that experienced a major nuclear war about 1 Ma, would there be any evidence of in the rocks in modern times?
Andrew asked:
What DOES happen when you get a bunch of geologists drunk?
For ease of answering, I have prepared this handy-dandy flowchart:
The lovely and cupcake-alicious E. Catherine Tobler had a couple of geology-related questions, which I have simplified because sooper sekrit reasons:
1) Pretend it’s before 1900–how do you test if a piece of jewelry is made from a meteorite?
After trawling around on the internet a bit, the most likely thing I could come up with is just checking if the jewelry is magnetic and then doing a double check with a streak plate… basically, if the piece is attracted to a magnet, that at least indicates it involves naturally magnetic minerals. And then if you scratch it on a ceramic streak plate and it leaves a metallic gray streak, that’d be a pretty good indicator that it’s at least not one of the usual suspects. Magnetite leaves a black streak and hematite leaves a red streak.
The streak test is a pretty old school one for mineral identification, so it would at least indicate that something weird is going on if you have this magnetic thing that’s not leaving an expected streak color. I know there are also chemical tests you can do to see if something contains nickel, which would be a big hint since all metallic meteorites are nickel/iron.
I don’t know precisely when the streak test came into wide use or when they really started cataloging streak color for minerals. But Mohs hardness scale was invented in 1812, and that kind of testing has been in use since basically the Greeks, just not standardized. Streak testing is an outgrowth of hardness testing, since when you rub something on a substance that is harder than it, you leave a streak of powdered mineral behind.
That said, I didn’t quite trust my own answer on this, so I e-mail my planetologist buddy John Dee since he knows space rocks so much better than I do. Here’s what he had to suggest:
Easy-peasy – just cut it in two, etch it with nitric acid and look for the Widmanstätten pattern. The pattern is formed when the iron core of a planetismal slowly cools and creates interlocking crystals. When the planetismal is later broken into pieces, it forms the stoney and iron meteorites.
Magnetism won’t be much use, as the planetismal probably wasn’t large enough to have an intrinsic magnetic field. And the streak pattern won’t be diagnostic because you’ll get the same result for native iron. But only a meteorite will give you the Widmanstätten pattern!
I don’t know if cutting the jewelry in half is actually an option, but even just etching the outside of it should reveal the Widmanstätten pattern. And so long as the jewelry was made without completely melting down the meteorite–if you just heated it enough to get it to bend instead, for example–that would be the best indicator for certain.
Question number two was a little less out of this world:
2) You’re in ancient Egypt. What kind of rock would you use to make a container for a liquid?
I found this awesome site that listed Ancient Egyptian quarries and mines and what each one produced. Which made answering this a lot easier. Basically, the material would need to be workable (well, presumably anything in the above quarries were things the Egyptians knew how to work), would need to be durable, would need to not react with what you put in it, and would need to be non-porous (to prevent seeping or desiccation).
So this eliminated things like schist (flaky), sandstone (potentially porous), and gypsum (too dang soft).
That leaves a lot of good options still:
Looking up all that information about quarries was really fun!
My friend Andrew Barton asked me, a bit out of the blue via twitter:
Given a now-earthlike planet terraformed 15 million years ago, which previously resembled an Earth-sized Iapetus or something, how obvious would the pre-terraforming rocks be, or what governs how deep they’d be now?
He also provided a bit more background as to the reason behind the question:
I’m still working out a lot of the details; this involves Esperanza, the terraformed habitable moon of HD 28185 b that was the setting of “The Paragon of Animals” in the March 2013 Analog, and hopefully additional stuff down the line. While tectonically active and geographically varied at present, it was entirely lifeless before the terraforming process began.
I should probably be ashamed to admit it, but I didn’t actually have an idea what Iapetus would be like. And didn’t look it up until this very moment (naughty, naughty) but I don’t think that would have changed the answer I sent him. Which is long and a bit rambling, but I was thinking it through as I went since the question was fairly general.
Tl;dr: That’s a really complicated question.
Obviously, I’m not the world’s greatest expert on this topic–any other geologists out there have thoughts? Did I get anything completely wrong? Just drop a note in the comments. I’m sure I didn’t think of everything.
Now you can read the whole enchilada for free! It’s a steamy but heart-wrenching story about a river and the course of its life as the world heats up and the mammals become ever tinier and more cute. Sandstones! Siltstones! Mudstones! Who will be swept away next? Will I need dental work from all those rocks I ate in Bremen? Will I overcome the cat vomit yellow sandstone or will it succeed in ruining my life? The answers can be found inside:
Sedimentary and climatic response to the Second Eocene Thermal Maximum in the McCullough Peaks Area, Bighorn Basin, Wyoming, U.S.A.
by Acks, Rachael, M.S., UNIVERSITY OF COLORADO AT BOULDER, 2013, 81 pages
Abstract:
The Paleocene-Eocene Thermal Maximum (PETM) was followed by a lesser hyperthermal event, called ETM2, at ∼53.7 Ma (Zachos et al., 2010). The carbon isotope excursion and global temperature increases for ETM2 were approximately half those of the PETM (Stap et al., 2010). The paleohydrologic response to this event in the continental interior of western North America is less well understood than the response to PETM warming. Although ETM2 is better known from marine than continental strata, the hyperthermal has been identified from outcrops of the alluvial Willwood Formation from the Deer Creek and Gilmore Hill sections of the McCullough Peaks area in the Bighorn Basin, Wyoming (Abels et al., 2012). The presence of ETM2 in Willwood Formation strata provides a rare opportunity to examine local continental climactic and sedimentary response to this hyperthermal.
Core drilled at Gilmore Hill was described and analyzed geochemically. The core consists of paleosols formed on mudrocks that are interbedded with siltstones and sandstones. Carbon isotope analysis of carbonate nodules from paleosols in the core shows that the top of the core, below a prominent yellow sandstone, most likely records the very beginning of the carbon isotope excursion that marks ETM2 (Maibauer and Bowen, unpublished data).The rest of the CIE was likely either not recorded due to sandstone deposition or removed by erosion prior to the deposition of the sandstone.
Analysis of bulk oxides in the paleosols using the methods of Sheldon et al. (2002) and Nordt and Driese (2010b) provides quantitative estimates of precipitation through the core section. The estimates reveal drying over the ∼15m leading up to ETM2. Red and brown paleosols, attributed to generally dry conditions, dominate the entire section below the onset of ETM2 and confirm drier conditions. In contrast, thick purple paleosols are associated with ETM2 at the Deer Creek site and suggest wetter conditions during most of the ETM2 interval. The prominent yellow sandstone at the top of the Gilmore Hill core was probably deposited during those wetter climate conditions.
The core displays distinct changes in stratigraphic architecture: the bottom ∼100m is mudrock-dominated and the top ∼100m is sandstone dominated. Several PETM studies have suggested that sediment coarsening in continental basins in the US and Spain developed in response to precipitation changes associated with global warming. Analysis of the Gilmore Hill core’s stratigraphic architecture in conjunction with carbon isotope and precipitation data shows that the prominent sandstone in the position of ETM2 was not caused by climate change. The sandstone is the uppermost part of the sandstone-rich interval whose base underlies ETM2 by more than 50m. This study shows that the shift from mudrock- to sandstone-dominated stratigraphy at Gilmore Hill, and possibly throughout the McCullough Peaks area, was not caused by climactic change associated with ETM2. While studies of PETM sections have suggested that the hyperthermal caused sediment coarsening in several different basins including the Bighorn Basin (e.g., Schmitz and Pujalte, 2007; Smith et al., 2008b; Foreman et al., 2012), this study suggests that the lesser magnitude ETM2 did not cross the necessary threshold to provoke a sedimentological response in the Bighorn Basin.
NK Jemisin tweeted this article this morning with an appended “Oh no:” massive (and it seems illegal) ocean fertilization project taking place off the coast of Canada. (And a little follow up here.) Oh no indeed. This is scientifically problematic for a lot of reasons, the two main ones being a) algal blooms ain’t exactly great for the surrounding waters and b) it most likely won’t have the intended effect. (And this doesn’t even touch on the grossness of the pretense used to convince the indigenous people in the area to go for it, that it was supposedly about the salmon population.)
Let me give you some background.
First off, “ocean fertilization” is the process of dumping some kind of nutrient that normally limits planktonic growth into an area of the ocean, thus letting the little guys eat their fill, have wild plankton sex, and increase their numbers rapidly. This works because basically every bit of the ocean has its planktonic growth limited by the scarcity of one or more nutrient (e.g.: Rivkin and Anderson, 1997); otherwise the oceans would be one giant algal matt. In some areas it’s nitrogen, in some it’s phosphate, in some it’s iron (because iron is necessary for photosynthesis).
Okay, so why do it?
The theory here is that the planktonic organisms (since there is more to ecosystem than algae, even if they’re the ones sucking up the iron for photosynthesis) contain carbon. Living things tend to do that. Additionally, quite a few planktonic organisms build themselves shells or internal structures from calcium carbonate, which also pulls carbon from the surrounding water. So a surge in these organisms should suck carbon out of the atmosphere and ocean waters, right? Then the organisms die, fall through the water column as marine snow, and take all the carbon with them. They get to the bottom waters, get buried, and hey presto, that carbon is now out of the short-term carbon cycle and into the long-term carbon cycle.
Because of course, the problems we are having right now are quite literally caused by us taking carbon from the long-term cycle and releasing it into the short term cycle at prodigious rates.
So why wouldn’t that work?
We actually talked about this topic when I took Oceanic Geochemistry about a year and a half ago. It sounds very simple on paper, like it really ought to work. However, recent research has shown that it might decrease planktonic populations long-term (not good) and that diatoms might suck up all the iron anyway, because diatoms are basically the freeloading college roommate of the plankton world, you know, like that guy who always drank all the beer in the fridge and never replaced it.
There’s an even more basic issue with the idea, however. In order for carbon to get into the long-term cycle, it needs to be buried, and before critters have the chance to eat it. The oceans are teeming with life, most of which are single-celled eukaryotic organisms and bacteria, who just love to eat anything organic. Even at the beginning of burial, when oxygen content is almost non-existent in the sediments, there are plenty of anaerobic bacteria who will just keep munching away and effectively poop out pyrite. (The process is far more complicated than that, of course, but there’s a reason you tend to see a lot of pyrite in super organic-rich shales. Or in shales that used to be organic-rich before the bacteria came along and ruined your life.)
For a long time the model of how sufficient carbon could be buried to give us our lovely black oil-producing shales depended on anoxic events (literally, no oxygen in the bottom waters), but it really seems to depend more on just burial rate. The way to get the carbon buried and out of the way is to inundate the bottom sediments with so much that the bacteria can’t possibly eat it all.
So then in order for this ocean fertilization idea to work, you’d have to up the productivity sufficiently and for a long enough period of time that you could provide a buffet so large for the organisms in the water column that they can’t possibly eat it all. Then
I’m back I’m thin section heaven at work, slaving over a hot petrographic microscope and continuing my second listen to the Vorkosigan saga audiobooks. (Excellent, by the way.) And I saw something a bit like this today:
Out rather, a bit like the portion marked with a T. A trilobite! Or rather a cross sectional cut through the carapace of one. I wish I could show you a picture of my actual thin section because it was way prettier and had the more characteristic hooked W shape. But I like that whole having a job thing so, no. Sorry.
But this is why it’s cool and why I love geology. Something like 340 MILLION years ago, a time so distant in the past that my brain can’t really comprehend it as anything other than wow a long fucking time ago, a little trilobite was hanging out on a shallow marine shelf. Because there were trilobites back then (and realize that no human being had ever seen a live one, we missed them by hundreds of millions of years). And this little trilobite presumably had an awesome trilobite life and hung out with his or her little trilobite friends and then one day died. Waves swept the little guy further out to sea, where he was given a proper burial in carbonate mud and…
Over three hundred million years later, met me.
I’m looking at a piece of rock that was the bottom of a tropical sea in the distant past long before biology every got around to even thinking of primates, key alone drinks involving little paper umbrellas. And I get to touch that. Every day I get a tiny window into an Earth alien to the one we live on now.
And that is why geology is cool.
Plus volcanic lightning because fuck yeah.
