h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Just something to get it started.

Palynological studies don't help much with this even though they tend to support megaflora inventories derived from examining leave fossils or such. Knowing what the floral community was can give an indication of climate that doesn't necessarily have a simple, direct relationship to altitude.

Even minor discrepancies in the lag rates, can change the altitude estimates radically. Oh well! What's next?

I am ready to speculate, but this is something I haven't studied.

What is known about the necessary aerodynamics of pollen? The reason I ask, is that while the paleoatmosphere has been thicker in the past, there still must be some gradation in air density with altitude. One pollen shape that works well in sealevel would fall out too soon at 1000m.

A treeline might be determinable by seeing if there's a discontinuity in quantity of seeds/pollen vs that of shrubs. I don't know if it'd be possible to determine relative climatic temperature, so this is perhaps not too helpful.

What can we steal from the biologists about leaf shapes? I know my sister studied the Costa Rican rainforest, and leaves there had driptips to encourage the constant precipitation to not stay around and weigh leaves down/rot them. Higher up, there was more likely to be fog than rain, and so the shapes of the leaves were more serrate to deal with that. What environmental influences can we suppose are universal about elevations that would necessarily shape the leaves of the plants at higher elevations?

Yes, that's the problem.

To give you a for instance: The Florissant Formation lies unconformitably on an eroded valley in the Pikes Peak Granite. This means the sediments were deposited after the batholith was uplifted and considerable overburden was eroded away. The formation is latest Eocene based on radiometric measurements.

In a 1950s study, the paleoelevation, based on floral analysis, was estimated at 900 meters, however, in the last 10 years or so, that interpretation has be challenged on palynological grounds. One estimate puts the paleoelevation at 2400 meters which is what it is now. That would mean it hasn't experienced further uplift for at least 34 million years while the rest of the region apparently has.

Consequently, the utility of palynological analysis for reliably and unequivocally estimating paleoelevation has become problematic.

I sort of thought this should be brainstorming so your suggestion about the aerodynamics of pollen grains might be worth investigating further since it doesn't rely solely on presumed correlations of flora with altitude but attempts in some fashion to estimate relative air pressure, which, if it could be done, would be a more direct or absolute estimate of elevation.

However, I don't see how you can do this. How could you distinguish the effects of pollenation efficiency from the effects of microclimate harshness, for example? Or differences that reflect heavy pollenators as opposed to light or insect mediated pollenators?

Obviously, floral or faunal assemblages are important indicators of contempory elevations. We talk about treeline or timberline and deadzones above certain elevations in certain regions of the world. But all those indicators depend heavily on the local climate, latitude and so on.

Even if we could reliably estimate gas concentrations, we know that oxygen, for example, is just as plentiful on the summit of Mount Everest as it is at sealevel. The difference is in the ambient air pressure, which means that above 24000-26000 feet the ability of mammals to pass oxygen across the tissue spaces separating the aveoli from the capillaries is severely obstructed by edema among other factors.

Is there something in the environment then that responds in a plastic or persistent fashion to air pressure?

Pollen is identifiable in two different ways. We can look at it, and see from this whether or not it belongs to any particular species. From this original study, we can determine if it's fern spore, gymnosperm or angiosperm or not. Many of the gymnosperms rely on wind pollination.

One of the things that helps create uniformity is that wind-pollinated plants usually create pollen that distributes out for miles and therefore could cover a large area, presumably one that stretches beyond the entire acceptable habitat of the plant in question because wind is unpredictable in direction. This could smooth over microclimate effects. This also gives us the cut off for the maximum distance any particular pollen flies.

I speculate, but don't know, that vertical barriers like taller trees or vertical sinks like nearby cliffs are not a huge problem, compared to the gross elevation information we wish to know.

Pollenation efficiency wouldn't show over geologic time scales. Either the plant can live in the particular environment or not, even if only one particular plant is able to live in the area every few years. Perhaps the plant is so scarce that this isn't a useful technique, or perhaps the plant is so self-fertile it doesn't need to make much pollen. Typically, though, plants that make windborne pollen make lots. I know this to my own personal detriment, as the Chinese Elms that West Hollywood has planted still cause me to sneeze at work here in Beverly Hills.

The other thing is the aerodynamics of the pollen grains themselves, which surely must change with atmospheric pressure, much as an airplane today changes it's angle of attack and it's wingshape with flaps and ailerons. There wouldn't be any evolutionary pressure for a pollen grain to be aerodynamic if the plant requires animal intermediaries, and this could be tested. We can create calibrations for how far any particular pollen shape and size will fly by creating our own, or by observing the the myriad that exist today in the field and making extrapolations.

It strikes me that there might be locations on the surface of the earth that are both liquid and severely reducing, like around volcanic areas or swamps. While the partial-pressure differential due to the difference in the mass of O2 and N2 would be small, it'd be pronounced in those locations.

The other half of this is even if it's too small to measure, the general reduction in atmospheric pressure would change how much gas in general is dissolved in any particular swampy tarn or burbling fumarole. If there's an excess of the reducing elements, then one could infer relative elevation, based on how little/how much oxidation is present based on what is expected from empirical measures in today's similar environments.

I was thinking that aerodynamic effects probably wouldn't be that important at the scale of pollen grains. I mean after all spiders can fly thousands of feet in the air for a good deal further than a thousand meters on a few strands of their thread mainly because of how light and small they are to begin with and they're mostly bigger than pollen grains. So I'm glad you came up with this partial pressure/oxidation idea. That's pretty brilliant I think.

So, let's assume we can do some experiments to establish that there is a clear relationship between rates of oxidation and air pressure and if we can, so far so good, but, what about temperature? Usually that's less at altitude so the question is would that difference basically nullify the change due to elevation or would it augment it?

I need to do some basic research on this and also look at what other chemical processes might be pressure sensitive because I'm not really sure at this point how we could interpret paleo-oxidation evidence.

For example, do we know that the reason the Triassic is famous for redbeds is because the atmospheric pressure was different? What does the relative abundance of hematites as opposed to limonites indicate?

Still I think we're on the right track here. I just haven't had time to really look into it or make up for having barely squeaked by in basic chemistry. So you are a God-send and thanks so much for being here and caring enough to share such totally cool insights.

As far as temperature is concerned, if you chose fumaroles, you probably could guess the temp they were at by measuring sulfur/arsenic/antimony amphoteric compounds. The atmospheric temp wouldn't be too relevant.

If you chose varves in swampy tarns, then there might be a temperature clue or not, based on the length of organic polymer chains, depending on how metamorphed the slate gets.

I remember hearing one speculation from my petrology prof about how redbeds might be due to changes in atmospheric partial pressure of O2 over time, and this might be due to the colonization of land by more sophisticated plants. But I heard that a long time ago.

Not giving up on pollen. You called me brilliant and so I'm going to be pig-headed.

It is true that pollen flies thousands of meters, but I bet the grains per m^2 drops off in a steady rate, as the distance from the source plants increases. This is why it'd be important to look for grains from a spp that doesn't grow in the environment that created the rock you are looking at.

I grow Asiatic lillies in my garden, and the pollen from them is large, sticky golden and obvious to the nekkid eye(bred that way-tis quite pretty) It falls down directly beneath the bloom, even while officious bees are having their orgiastic snack. As they fly/lumber away fully laden, you can see their legs glow. If you found grains of these spp. 10m away from my garden, I'd be surprised.

You could compare the drop-off from the pollen of a lilly species to the gymnosperm species and determine paleo-climatic wind direction. Once you knew this, you could find the 2D planar 'minimum' of the stereocurve you are about to draw.

If the pollen density drop off in one location is a smoother curve than in another, you could compare curves and infer that there is less thick of an atmosphere. Whether this is suceptible to fine and constant measurement or merely gives qualitative data, I don't know.