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

I have a few questions, xyroth, and I apologize in advance for imposing on you but you'll maybe see why I'm interested further down.

How was the sampling done? Did the climatic estimations take into account the latitude of the dendrochronological samples or the lag gradients due to differences in elevation? How was the macroclimate derived from the microclimates represented by the dendrochronological samples, in other words?

And how were such derivations extended to the paleoclimates? Most importantly, what in the ice cores was calibrated? Were the gas mixtures compared to palynological samples in the same cores? Did they correlate well?

Coincidentally, this issue arose recently when I received a challenge from one of my mentors to determine what if anything could replace the somewhat unreliable palynological methods used in deriving paleoelevations. Depending on the lag rate estimates, for example, the elevation estimates could vary radically, sometimes in direct contradiction of the geological data.

Consequently, deducing climates, even microclimates, from palynological evidence is somewhat problematic due to elevation and latitude gradients and the overall effect of the global climate. We sometimes end up in a sort of circular reasoning trap where we derive microclimates in part from the global climate and the global climate from the aggregate of the microclimates.

Consequently, I'm not sure it's quite as cut and dried as you imply.

For example, a subtropical to wet temperate flora might thrive in a variety of geographical zones, anywhere from sea-level to 2500 meters ialtitude and from latitudes of 20-30 or more degrees north or south. Various combinations are possible such that the floral might thrive at high latitudes if the elevation is near sea level >> and << the coastal microclimate is not overly influenced by cold ocean currents.

The present day California coast is an excellent example of a microclimate that is influenced by such currents to such an extent that similar microclimates can be observed in the fossil record of regions that showed considerably more elevation relief, and current microclimates at lower latitudes and even higher elevations. Even so, the flora do not strictly correlate between these regions.

In short, it's not as simple as it looks and I would just love to have something like an ice core from a mountain glacier remnant that would settle things without all the qualifications.

Hey Rita - the new paragraph reads just fine now. Tremendously flattered that you mentioned me by name, but this will almost certainly be stripped out by a sub-ed after your entry is chosen by a scout. So the ammonite link should probably just be there on its own. Glad you liked it by the way.
This is a tricky subject to write a short entry on because of the sheer amount of information you have to encapsulate in such a short space. However, I think you've done an excellent job, and to expand on the methods given would take up a whole book. For anyone wishing to read a fuller account I can recommend 'The Dating Game' by Cherry Lewis (ISBN: 0521893127) and 'The Architects of Eternity' by Richard Corfield (ISBN: 0747264740). Corfield is a bit of a 'flash' writer though, and doesn't appeal to everyone's tastes. He makes a couple of glaring errors, including the statement that the Silurian and Ordovician periods were named after palaeolithic border tribes, when they were in fact Iron Age tribes. He also fair skips over the contributions of Buckland, Smith, Mantell an De La Beche in an effort to get to his own subject. But when he does get going on a subject he obviously loves, the book really takes off.

Ooer. Perhaps I should stick to short posts.

I like the article as it stands. The way it is written, most of the unfamiliar terms can be inferred at least categorically from context. 'Igneous' might not be known, but lava/magma/intrusion imply something volcanic, and this can be used to search the Guide, or other sources.

Truly, each of the subheadings that Rita has included here are well studied and can be quite interesting topics on their own. I don't think they need to be elaborated more than they are already.

I think that climatology is very interesting. Water-ice is clearly can be solid for long periods of time, and then huge sheets of it sometimes flow like a glass. Perhaps Researcher Xyroth would be kind enough to write up an entry about it?

Excellent suggestion, about writing up the ice.

I'm going to let this one stand for awhile. Thanks to everyone for making it a collaborative effort.

Is this complete now, Rita, or are you still awaiting a reply from xyroth?

I think we can deal with the ice issues in a separate entry. Let's go with it, okay?

I'm glad you will not be waiting for an article about the ice cores, because I don't have time to write one right now.

however, I will try and answer with as much detail as I can, and anyone else who wants to is welcome to give it a try.

first, how was the sampling done. they used the entire dendrochronology database (including the geographical info).

What they did was take the information which was closely related geographically, and using current information about what climatic conditions different species prosper under were able to correlate the dendro data with various climatalogical variables (including pressure, average yearly temperature, etc). they then cross checked this against the existing records for climate to further verify their assumptions.

this left them with dendroclimatology. they then used the dendro data to push back the database of yearly climate to the limit of the timeline (between four and eight thousand years depending on the location).

this they verified using seeds and pollen found in sedimentary layers in lakes.

having further confirmed their assumptions using these methods, they then did mass spectroscopy of the gases trapped in ice cores (and their relative isotopic abundancies) to correlate these extravariables against the standard climatological variables mentioned earlier.

because the planetary climate has an effect on the growth of vegatation including trees and water borne algae, which in turn affects the amount of different isotopes recirculated through the atmosphere, which then gets trapped in fresh snowfall (and then compacted into the ice cores), it all hangs together fairly well.

there are problems however. in particular, the current information extracted from the ice cores, particulary the deep time results, don't actually correspond with the output of the different climatological models currently being used to study global warming.

as if that wasn't bad enough, the different models do agree with lots of the data, just not the same bits. this sort of implies a fairly deep level of ignorance of the principles of planetary climate, as well as a pretty poor integration of the current knowledge of the science into a decently consistent whole.

as to microclimate, I am fairly sure that it was only relevant to limiting the values on the individual climatic variables.

Unfortunately, the data sources have the same problem as in cosmology. the items that it would be particularly nice to have detailed information about grows rapidly more sparse the further back you go.

for example you can deduce the climate from the dendro and sedimentary data, but not really the other way around.

most of the work appears to have been done around the investigation of the global climate over deep time.

if you want any further information, I will see what I can find, but it might take a while. life is a bit hectic at the moment.

I understand your plight. If you want you can put something in the Collaborative GeoLab when you have time. Thanks.

Here's the URL for that: http://www.bbc.co.uk/dna/h2g2/alabaster/A866351

I will try and get around to it. in the mean time, don't you think that page should be "not for review"?

I didn't think I'd submitted it for review or anything else. Did I miss something?

when you are creating a page that is not for review, which that one looks like it should be, then ticking the box "not for review" under the edit box will stop anyone from jumping the gun and submitting something which isn't ready.

some pages are generally not for review as well.

Is this still here? Oi! Scouts!

Your Guide Entry has just been picked from Peer Review by one of our Scouts, and is now heading off into the Editorial Process, which ends with publication in the Edited Guide. We've therefore moved this Review Conversation out of Peer Review and to the entry itself.

If you'd like to know what happens now, check out the page on 'What Happens after your Entry has been Recommended?' at EditedGuide-Process. We hope this explains everything.

Thanks for contributing to the Edited Guide!

Well done Rita!

A fine entry for the Edited Guide

J

Thanks and thanks too for everyone's help.

Congratulations!

Wow, I'm miles behind! A deserving entry indeed!

Thanks, Woodpidgeon, for your kind words.