The Geology Thread
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28-07-2016, 02:34 AM
RE: The Geology Thread
I too was attending undergraduate classes in the subject a long, long time ago and back then Plate Tectonics didn't have the near-universal acceptance that it does now.

One of the older academics was of the "old school" when it came to explaining orogenic uplift. It was all down to the crust "springing up" when subjected to too much pressure from overlying sediments and igneous outpourings as I recall. Meanwhile on the course in vulcanology the somewhat younger member of staff was telling us all about plate tectonics.

That made for some quite lively discussions during tutorials. The plate tectonic theory just made so much sense and was so much simpler than the previous orthodox explanation. A case of Occam's Razor methinks.

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28-07-2016, 08:37 AM
RE: The Geology Thread
(27-07-2016 10:45 AM)Full Circle Wrote:  I’ll start it up then. Just read...

"Evolution may have been waiting for a decent breath of oxygen, said researcher Chris Reinhard. And that was hard to come by. His research team is tracking down O2 concentrations in oceans, where earliest animals evolved.

By doing so, they have jumped into the middle of a heated scientific debate on what rising oxygen did, if anything, to charge up evolutionary eras. Reinhard, a geochemist from the Georgia Institute of Technology, is shaking up conventional thinking with the help of computer modeling.”

https://www.sciencedaily.com/releases/20...151511.htm

Oxygen is fundamental for respiring life, the chemosynthesizing and photosynthesizing organisms were doing just fine for quite a long time. But if animals (and some photosynthetic reactions also need oxygen avialable) were to arrive, they'd clearly need oxygen.

Things we know:
The early Earth atmosphere and oceans were largely devoid of oxygen, but once photosynthesizing life originated and began pumping oxygen into the oceans...there was still no free oxygen. Why? Because the oceans had so much iron in them that the oxygen would react with it and create a suite of iron oxides. This resulted in deposition of Banded Iron Formation (BIFs). Once enough of the iron had been scavenged from the ocean, free oxygen in the ocean and in the atmosphere could begin to build up.

[Image: nature13068-f1.jpg]

The above image is far more diagrammatic and hypothetical than it probably seems. But the pattern is largely not disputed (although that big bump at ~2.2Ga is new to me and is probably bullshit). We suspect two periods of substantial oxygen rise. The first of which helped the Eukaryotes evolve and the second appears to have allowed animal life to originate. But we don't have an accurate way of measuring atmospheric oxygen concentrations in most of the geologic record (we can be pretty accurate in some cases when we have leaves preserved in the fossil record or other proxies, like giant terrestrial arthropods. But those organisms are long after the Great Oxygenation Events when animal and plants were well established).

Sounds like this modeling paper revolved around trying to better understand the heterogeneity of the timing and location of the oxygen-rich (which is oxymoronic considering how low the oxygen would have been at this time) waters in the Proterozoic oceans. Which is interesting because one might have assumed that the shallow waters were where metazoan life would have gotten started, but that may be less oxygenated.

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28-07-2016, 09:17 AM
RE: The Geology Thread
(28-07-2016 01:58 AM)Thumpalumpacus Wrote:  I took Geology 101 about three centuries ago, it was one of the classes that got my rational brain fired up. The first six weeks were about climate and the water cycle -- at first I was very much WTF?! But as the course unfolded, I realized how atmosphere, lithosphere, and climate interact.

Yeah, I think it's a pretty big shock to a lot of students to see how diversified geology is. Especially since so many of them take geology to avoid physics or chemistry, but then we start teaching them concepts in physics and chemistry.

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28-07-2016, 11:18 AM
RE: The Geology Thread
Science, i fucking love science. Heart Banana_zorro

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28-07-2016, 05:09 PM
RE: The Geology Thread
(28-07-2016 09:17 AM)TheBeardedDude Wrote:  
(28-07-2016 01:58 AM)Thumpalumpacus Wrote:  I took Geology 101 about three centuries ago, it was one of the classes that got my rational brain fired up. The first six weeks were about climate and the water cycle -- at first I was very much WTF?! But as the course unfolded, I realized how atmosphere, lithosphere, and climate interact.

Yeah, I think it's a pretty big shock to a lot of students to see how diversified geology is. Especially since so many of them take geology to avoid physics or chemistry, but then we start teaching them concepts in physics and chemistry.

Optical mineralogy is typically rated as the hardest second-year science courses on most campuses and beats organic chem hands down.

[Image: Spherulite_zpsmcgwyhzv.jpg]

Spherulitic rhyolite that's gone to an extreme granophyric texture. Sorry about the distortion at the image edges, the camera on our scope doesn't focus properly.

This is volcanic glass that has crystalized. Glass isn't stable over long time periods and devitrifies after a few tens of thousands of years. As it does so it forms mineral grains, starting at a central nucleation point and progressing outward. The mineral grains near the center are very fine but the ones further out are considerably coarser. This example has gone to the extreme of producing a texture more commonly observed in granites where the quartz and feldspar (white mineral in granite) are intergrown. In hand sample these look like tiny spheres, hence the name.

[Image: hs_i6287_0.jpg]

This picture was taken by shining polarized light through a 30 micron thick sample of the rock and then passing that light through a second polarizing film oriented at 90 degrees to the first. Simply passing light through two polarizers oriented at right angles to one another should block all light. By placing the mineral sample between the two polarizers some very cool physics happens involving splitting and recombining the light to produce interference colours but that's a whole other story.

It makes mineral identification uch simpler and allows for some estimates on composition if you know what you're doing. Also very colourful. No LSD required. Here's a gabbro, sometimes referred to as "black granite" by Phillistines.

[Image: BH250-192a.jpg]

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10-08-2016, 02:28 AM
RE: The Geology Thread
Motorways reveal evidence of massive tropical storms 200 million years ago

http://www.bristol.ac.uk/news/2016/augus...ssils.html

Research on rocks beneath one of the West Country's busiest motorway junctions has revealed unexpected evidence of major flooding events across southern England millions of years ago.

What I think is great about this article is that an undergraduate student used borehole sample material taken 25 years ago to find something new and unexpected about our distant past.

Science..........doncha love it!

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