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Grepley

Science Salon: 2017 January

38 posts in this topic

Posted (edited)

One of the reasons that I was attracted to Geosciences is that it had undergone a paradigm shift most recently of all the major sciences, in the mid-1960s to 1970s. 

For the first paper, I am presenting a seminal paper on plate tectonics: Vine and Matthews, Magnetic Anomalies over Mid-Ocean Ridges, Nature, pp. 947-949, 1963. [pdf] This is a short paper to start out, only three pages. I am also presenting some background material to make it more comprehensible. 

Continental Drift - evidence that plates have moved
Alfred Wegener (1880-1930) was a climatologist that provided five major lines of evidence that all of the continents had all been connected into one mass that broke up about 300 million years ago (Pangea, which he first named): Continental Drift. This evidence: fit of continental shelves like puzzle pieces, paleoclimate / glacial striations, a mountain range spanning continents, same fossils on different continents, and connection of old continental material (cratons). He published a book, The Origin of Continents and Oceans, in 1915 (note that the theory of plate tectonics was still controversial when republished in 1966); more accessible online and shorter is his first lecture, The Origin of Continents, in 1912 [pdf]. This evidence was not easily available to European geologists to visit, so his work in geology was largely dismissed; though he did die a very respected climatologist with a book on climatology that was used for many decades. Wegener did not have a mechanism for Continental Drift to start with, but finally came up with the idea that centrifugal force towards the equator caused a "pole-fleeing" force. (Though the competing idea was not much better, that the interior of the earth was cooling and mountain ranges were the wrinkles on a shrinking earth. This was the leading hypothesis through plate tectonics. I like to think of it as the apple-head doll theory.)

A shorter and more succinct history of Alfred Wegener and Continental Drift:

*****

Seafloor Spreading / Divergent Plate Tectonics, Vine and Matthews (and Morley)
"Striped" magnetic anomalies on the ocean seafloor were known from military use of magnetometers in the late 1940s and 1950s in an attempt to find enemy submarines.
The perspicacious might have already spotted a cheat sheet on Vine and Matthews from The Geological Society Pioneers of Plate Tectonics. 
Embedded video of divergent plate tectonics at the mid-Atlantic oceanic ridge, with magnetic pole reversals.
Divergent plate margins have a (half) spreading rate - from the center in each direction - of about 1-5 mm/yr, or about the rate that fingernails grow.

*****

Essential concepts for paper:
Oceanic Ridges
are about 2 km or less deep, vs 4 km average oceanic depth; often found in the center of the ocean, such as the Atlantic.
Dark grey in the map below:
HeezenTharp_700.jpg

Age of oceanic crust; note that the youngest crust is at the ocean ridges, and that the oldest oceanic crust is about 190 My - much younger than the earth's age of 4.6 By. 
(We are making oceanic crust at the ridges - this is half of plate tectonics - but what about destroying it?!?! - that's the second half).
oldcontinental-rock.png

Geomagnetic Reversals 
Earth's geomagnetic field is powered by the geodynamo - rotation of the outside liquid iron core. The first simulation of the geodynamo from first physical principals (Glatzmaier et al., Nature 401, 885-890, 1999 - not online) also captured a geomagnetic reversal in the simulation. Unfortunately I have not been able to find a video online of the reversal now (has existed in the past), but this slide show [pdf] shows the normal, 500 yrs before reversal, maximum reversal, and 500 years after, starting on page 4 - in general it is a good introduction to the magnetic field and reversals. (Note: Glatzmaier et al. simulation took 1,200 years / 1.2 kyr to flip, while Earth's magnetic field flips in about 3,000 yrs / 3 kyrs.) 
reversal-460.jpg

For those that really want to dig into the geodynamo, on Earth, large planets, and Titian, a one hour lecture by Gary Glatzmaier at NASA; there are chapters at the beginning to take you to the part of the video you are interested in.

 

Edited by Grepley

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Posted (edited)

I will give it a shot.

Geomagnetic anomalies? How are they explaining it in the paper. The science of it?

Given the article,  I wish to take a current and larger view of the subject of geomagnetic.

Quote

Swarm is a European Space Agency (ESA) mission to study the Earth's magnetic field. High-precision and high-resolution measurements of the strength, direction and variations of the Earth's magnetic field, complemented by precise navigation, accelerometer and electric field measurements, will provide data essential for modelling the geomagnetic field and its interaction with other physical aspects of the Earth system. The results will offer a unique view of the inside of the Earth from space, enabling the composition and processes of the interior to be studied in detail and increase our knowledge of atmospheric processes and ocean circulation patterns that affect climate and weather.

A small video to help orientate perspective on the article and then back to the article submitted.

Quote

 

 

Edited by PlatoHagel

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I have one request:   that people responding in the thread actually read the paper.  In order to raise quality, a decent signal to noise ratio must be maintained.   

 

Having read the paper and the materials, I have questions for zee geologist:

 

1.  Wegener's theory took about 40 years for it to catch on, but his five points of evidence are really quite compelling.   I take it the past model of the Earth didn't include a liquid core?  But that doesn't make sense because of volcanic activity...   Anywho 40 years seems like a long time to overcome what seems, if not obvious, but quite convincing.   Why?

 

2.  I know going to Antarctica and drilling through ice to get to the soil is a pain and expensive, but with global warming, has there been any fossil digs in Antarctica?

 

3.  Would Wegener be considered the Darwin of geology?  As in, his ideas are core to modern geology, or are there any other geologists who might have contributed more.  On that note, we rarely get famous geologists in the spotlight.   Who are some important ones?

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Posted (edited)

1. Wegener kept adding evidence throughout his life, and it was continued mainly by South American geologists, where much of the evidence was available. His work was discounted and forgotten for two, perhaps three reasons. Perhaps one reason was that he was working outside his field; when people think of "poor Wegener," he was one of the foremost climatologists in his day, and hugely successful inside his field. Thus Continental Drift was more of a passionate hobby for him. (We have a good record of his piecing things together, since charmingly he wrote letters back to his wife from Greenland outlining his thoughts.) The best evidence was available in Antarctica, South America, and Africa - while European geologists rarely got there to see the original evidence, especially in the 1920s (Depression). The main reason was not having a mechanism - including Wegener, all geologists could think of was continents plowing through oceanic crust, which was frankly impossible. Plus, what would be the driving force? Wegener late in his all-to-short life (died on his fourth expedition to Greenland at 50) proposed centrifugal force pushing continents outward from the South Pole to the equator... falls far short of plowing continents! (also did not explain his observation of coal in polar regions... moving from tropics to pole). Even after Vine and Matthews (and corresponding work on convergent plate boundaries in the early 1970s), plate tectonics was not an "ah ha" moment - it was hugely controversial through the 1960s-1970s. (The last place to concede was Caltech... usu. 1-2 place in Earth Sciences according to US News). 

What geologists knew at the time. Due to inertia, it was obvious that the earth had a very heavy core; based on meteorites high iron content and relative lack of abundance of iron at the earth's surface, the core was thought to be iron. So we knew that the core was iron and the approximate size (half the distance to the earth's surface, and about 1/8 the volume of the earth). We knew from mantle xenoliths ("foreign rocks") - chunks of mantle ripped up by volcanoes and brought to the surface - that at least the near interior was denser than continental crust and oceanic crust. The near layer was thought to be molten, such that the thicker, lighter continental crust at 30 km or more floated higher than the thin oceanic crust of about 10 km - explaining the topographic difference between the continents and ocean basins, and providing a source for volcanic magma. The earth was thought to be cooling, mainly through conduction. Lord Kelvin, a physicist, calculated the rate of cooling through conduction and set the age at 20-40 Ma in 1862. At about the same time geologists, guided by Lyell's Principal of Uniformitarianism, looked at modern rates of deposition and the sequence of rocks in England, and came up with an age of 400 Ma (partly by chance a pretty good estimate of the total ages of rock exposed in England) - initially Lord Kelvin won because physics and equations, but by Wegener's time, especially with the first Uranium-Lead dating starting in 1907, the older age was accepted as a minimum age. The main theory of mountain formation, etc. was that earth was cooling and shrinking, making mountain ranges and sinking land bridges. Land bridges were thought to be a corridor for plants and animals to travel to far-flung continents (hey, it did work for the Bering Land Straits), and could contain the evidence for continuing mountain ranges, etc. Problems with this theory were that mountain ranges were vastly different ages, which required finagling, and that it would be hard to sink land bridges since continents should float higher than the ocean basins. But in general, parts of the earth were thought to be moving up and down in place. The earth's magnetic field was thought to be due to the iron core, primarily a huge static magnet (which we now know would decay over about 20 Myr - we do need the dynamo / magnetohydrodynamics of the outer liquid core to keep things going!). 

Our first good look at the interior of the earth was through seismic tomography - using seismic stations to image the inside of the earth. There are two types of waves, P / primary (think of compressing a section of a pulled-out slinky - this compression travels through the slinky when released.) and S / secondary or shear (take a jump rope pulled out, and have one person wave it up and down - moves side-to-side along the direction of travel). S waves travel more slowly through plastic / hot material, and do not travel at all through liquids - voila the liquid core is imaged, and we know that the mantle is solid, though parts are more plastic than others. Many advances in geology are due as riders to military applications (think of the magnetometers used to look for submarines, and finding a "stripey" sea floor magnetic pattern). We could tell from just a few seismic stations around the world that the outer core was liquid; more detailed tomography / "pictures" were due to the dense network of seismic stations installed for the purpose of monitoring atomic bomb testing in other countries starting in the 1950s, and especially ramped up to determine the *size* of the atomic bomb tests after the first SALT treaty in 1971, to determine if the Russians were following the treaty. The dense network is what allowed us to start imaging the thicknesses of the oceanic plate, and seeing what happened at convergent plate margins where oceanic plates are subducted - part II of plate tectonics. Also, the entire mantle was found to be solid... though the solid mantle plates are on a more viscous layer, so it acts as a "plastic" non-Newtonian fluid on longer timescales. (The viscosity of the mantle varies from 10^19 to 10^22 Pascal/seconds - one of the few things to cover so many orders of magnitude in geosciences. In comparison, the viscosity of glass is 10^12 Pa/s). 

*****
2. Glaciers require a) land and b) source of water to form. (During the ice ages, current continental configuration at 60 degrees latitude North is a perfect place for them to form, since there is a source of water at the North pole and interspersed throughout that latitude, and broad landmasses in Canada and Europe to put them on. Ice ages are also determined by fortuitous continental configuration as well as climate.) There are places in the interior of Antarctica that do not receive enough water to form ice shields / glaciers (Antarctica Dry Valleys), and the peninsula trailing off from Antarctica does not have the land mass to support a glacier - for example, here is a report of 70 Ma dinosaur fossils from 2016. Scott's ill-fated expedition to the poles failed partly because he would not give up on transporting the samples back, which contained numerous fossils.

*****
3. For the equivalent of Darwin, I would choose Lyell and his Principal of Uniformitarianism. Darwin took this book aboard the Beagle, and it was instrumental in forming his thoughts on finch beaks and evolution. Cribbing from my blog: 'I should probably read this; I've read excerpts, and I've heard the entire argument is very well laid-out. I view it as mostly of historical interest, both for standing against the catastrophism of Creationism and influencing Darwin in his thinking (though it must be noted Lyell did not believe Darwin's arguments for biologic evolution). Lyell did lean too hard in the direction of non-catastrophism, a reaction against the Creationists. As geo-folk we do learn the "weak" version of Lyell, which essentially boils down to "physics / science has always worked." ' Since Lyell was reacting against Biblical Catastrophism, he held that only processes we see today result in forming the deep time recorded by the Earth - he did underestimate that rare events (meteorite impacts, Yellowstone-scale caldera volcanic events etc) and the of course missed the evolution of the solar system in forming Earth (e.g. impact with Mars-sized object that created moon / drove off first atmosphere / current atmosphere from comet bombardment). Lyell's Principals of Geology online. 

Wegener is certainly heralded as the father of plate motion, based on all of the evidence that he accumulated for his theory of Continental Drift. Unfortunately his book, Origin of Continents and Oceans, was only translated from German to English in 1966 and is not available online, but I would recommend the lecture of 1912 linked above. I have read this book for historical interest and it is fascinating. He would be the equivalent of Rosalind Franklin, who provided the X-ray crystallography necessary to discover the double helix (BTW, her postdoc directly continued another line of research of hers on viruses that resulted in the Nobel Prize for him after Franklin had died - so she was heavily involved in the acquisition of two Nobels, particularly the second. Not a one-shot wonder).

Hess developed the theoretical framework for plate tectonics in 1962, one year before Vine and Matthews provided evidence of sea-floor spreading. By this time there was enough evidence to start putting plate tectonics together, and his work has largely been overshadowed by the people providing actual evidence (such as Vine and Matthews, and an even broader cluster of researchers for plate subduction at trenches / convergent plate boundaries.) In general, with new sources of data from magnetometers and seismic stations, plate tectonics was "in the air" - rather like the race for the structure of DNA / double helix - but there were a lot of "winners." So we have no equivalent of Watson and Crick, but Vine and Matthews comes close for providing the first evidence of seafloor spreading.

Another big prize was the age of the earth, won by Clair Patterson - I would like to do this as a seminal paper in the future, so not much more about him! He had a very clever idea, so he definitively won the race for that. (We did have an idea of the age of the earth from dating meteorites, he was the first person to figure out how to date the earth directly.) 

Edited by Grepley

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I have a question?

 

Is this more about the science of Climate Change? Be truthful.

 
 
...... added to this post 2 minutes later:
 
1 minute ago, PlatoHagel said:

I have a question?

 

Is this more about the science of Climate Change? Be truthful.

Secondly Op was adjusted to include information I am sharing. This is all I have to add. Thanks

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Posted (edited)

I had not finished my post last night, with information added starting at mid-ocean ridges. I also decided to put up a video of sea-floor spreading now, rather than waiting until after discussion, since it would be hidden farther down in the thread. Now all of the information I want to present prior to discussion is there. 

Plate Tectonics / Divergent Plate Boundaries has / have nothing to do with anthropogenic climate change. Plate Tectonics is part of long-term climate change; please read my response to Kisai, which talks about the importance of a mixture of ocean and landmasses at 60 degrees latitude N, which allow the formation of glaciers - landmasses to put them on, and water sources to "feed" them. There would be no ice ages without a similar configuration of continents and landmasses (the other factor was decrease in CO2 levels throughout the past 55 Myrs). The growth and degradation of ice sheets are directly correlated with solar insolation due to obliquity changes (axial tilt) and precession, and are correlated with a much stronger reaction to the solar insolation changes during obliquity / 100 kyr cycle. 

Edited by Grepley

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Posted (edited)

My apology.  Matthew's name pops up in a lot of places regarding the dissemination of information regarding climate change, but I am interested with what's going on with Earth sciences and the picture of earth we are receiving. I will try and contain myself to the subject.

Quote

cascadia750.jpg

The red line outlines the Juan de Fuca plate that is moving eastward, shoved under the continental North American plate and generating megathrust earthquakes.

Can the current seismic events being recorded lately be seen as a historical diagram of these magnetic anomalies as in any documented examples given by Vine and Matthews? Signs about the impending polarity change as from realignment?

Edited by PlatoHagel

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Finally free. Read all material.

Concerning evidence of glaciation on the southern continents, they mention the traces left by rocks being dragged by glaciers, but wouldn't those traces be beyond eroded by now?

And concerning the geological fit, it brings me to another question: how does continental material get formed, clearly the process seems separate from the oceanic crust, and much slower. What consequence do you see in those processes and the comprehensiveness of marine fossil record?

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Posted (edited)

@PlatoHagel: (quote):
 

Quote

Can the current seismic events being recorded lately be seen as a historical diagram of these magnetic anomalies as in any documented examples given by Vine and Matthews? Signs about the impending polarity change as from realignment?

 

1. The magnetic field aligns magnetic minerals (magnetite and other iron-bearing minerals) as they crystallize out of magma. (Or, on land, crystallize in lava or settle out of water into sediments). This the is actual record that we are reading with magnetometers. Which way minerals are aligned on the seafloor has no influence on plate boundary motion or numbers / intensity / etc. of earthquakes. (The subduction of the oceanic ridge / young oceanic crust in the Juan de Fuca / Gorda platelet under North America causes more stick-slip motion and fewer and more intense earthquakes. That is not due to the magnetic anomalies, however.)

*****

2. The Nova program you linked above is an over-dramatization of what might happen, just like the idea that Yellowstone will explode tomorrow, etc. They get more viewers if they make it as dramatic and "relevant to people" (ptah) as possible. [Note that I have seen over-dramatization of my own personal research as well - by a friend in the media - that is just what the media does, even though she understood the more likely, less dramatic option as well.] The earth's magnetic field is not a pure dipole, and it often strengthens and weakens without resulting in a magnetic reversal.  

Also, the last magnetic reversal occurred 41,000 years ago, and lasted 440 years. (Note also that once the magnetic field weakens and is a multi-dipole moment, at the height of a geomagnetic reversal or excursion, it can do one of two things: reform in reverse polarity (reversal), or reform in the previous polarity (excursion) - once it is gone, it is mostly up to chance which direction it reforms.)

The reality is that we (well, the European Space Agency) now has satellites in space to monitor very short-term fluxes in the earth's magnetic field - SWARM - this is data on a new time scale and detail even beyond earth-bound and balloon magnetometers, and we cannot interpret it as a magnetic flip. What has actually happened:

Quote

It shows clearly that the field has weakened by about 3.5% at high latitudes over North America, while it has strengthened about 2% over Asia. The region where the field is at its weakest – the South Atlantic Anomaly – has moved steadily westward and weakened further by about 2%.

SWARM data through 2016 - ESA - includes videos. Facts are much less dramatic, hey? (What the fuss was about was the fast rate of change, not absolute change, but this is our first good measurement of rate of change, so we don't know that much about what it means.)

Data that we have had previously includes records of magnetic field strength averaged over about a decade from cosmogenic 10Beryllium, which is formed in the atmosphere by cosmic rays and rained out immediately. We can get a record from drilling the Antarctic ice sheets back a few million years, and measuring the 10Be contained in sections of the ice core. 10Be and magnetic field strength are anti-correlated; the weaker the magnetic field, the more cosmogenic radiation (mostly hydrogen accelerated in supernova explosions) reaches the earth, the higher the production of 10Be. The magnetic field weakened by about 50% about 15 kyr ago (and hey, no magnetic reversal!)

Beyond that, we have seafloor records out to 190 Ma, and good records on land. The strength of alignment of magnetic minerals is also affected by depth of the mid-ocean ridge while they are being formed, so we need to make assumptions for our continuous seafloor record (as well as making assumptions about steady sea-floor spreading rate due to sparse dating). This is checked with field strength and well-dated records on land, which are abundant over the past few hundred million years.

geomagneticpolarity.jpg

We also have further records that fill in the record to a coarser level using lava and lake sediment records on land, but I want to concentrate on the timescale of the sea-floor records.

Note that the magnetic field reversals have changed over time - there is the 30 Myr normal Cretaceous Superchron. (Chron is the term for the period of time the field remains normal or reversed.) Post-Cretaceous, the rate of magnetic field reversals has been gradually speeding up. (Note: this is evidence that Creationists use for a young earth; they hold magnetic field reversals are constant, thus later time is compressed.) The actual explanation is much more simple, however. The earth is cooling, and the earth's iron core is continuing to solidify, decreasing the thickness of the outer molten iron core (and producing 5-10% of the earth's total heat budget). This decreasing thickness of the molten geodynamo has led to more frequent magnetic field reversals through time. However, time to magnetic reversal is still highly variable. 

Edited by Grepley

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Also, to start organizing the book reading for March, I have selected 5 books up for voting (then, if the book is too big, a vote will be carried out to select the chapters that all will read):

Campbell's Biology, it's a big one, but it's a classic and very wide in scope, which will allow the readers to form a solid big picture view of biology for subsequent reading. It's not very detailed however, it's an overview, and since it's a big one, we will have to select chapters anyway as a minimum reading.

The Cell, by Cooper and Hausman, Excellent book detailing the various processes and mechanisms that allow life to function in the first place. I preferred this one to a more thorough Molecular biology of the cell to avoid overloading with molecular details of pathways and their proteins, which would be excessive for a first time.

Developmental Biology, by Gilbert, the classic in its domain, it allows for very practical and detailed exemples of cellular biology in the development (so mainly embryology) of a wide range of models, while avoiding getting into the lengths the previous book goes into. The drawback is that it assumes some previous knowledge (well, just that some things will make a lot of sense if you read the previous book for example), but that's what I am here for.

Harper's Illustrated Biochemistry, It's much more detailed and low-level (in terms of what it focuses on) but on the other hand, those are the building blocks of all Life on earth, so it might be the logical place to start, just like students do.

Introduction to genetic analysis, by Griffiths, Wessler, Carroll and Doebley. It's a simple one that carries its own weight (meaning that they explain how DNA works in it, so no knowledge is presupposed), it covers a lot of fields of study in biology, it's very practical (it explains how the technology works, how the studies are carried out) and it's probably the most gratifying of the list since it can easily be followed and what is presented can be conceptually used readily.

 

All of those are 700+ pages, which means that we need to figure out what those who want to participate predict they could read in less than two months, and then vote the chapters in the one that gets selected. I avoided more specialized (but maybe more interesting) books like Introduction to immunology, or Neurosciences, because I think understanding the basics is more important and allows for a much better appreciation of everything else that might come after. 

The way you vote is that you write the titles of the books you might want to read, and the one with the most voices is selected. Please write the number of pages you think you can read as well

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Posted (edited)

1 hour ago, slade19 said:

Finally free. Read all material.

Concerning evidence of glaciation on the southern continents, they mention the traces left by rocks being dragged by glaciers, but wouldn't those traces be beyond eroded by now?

And concerning the geological fit, it brings me to another question: how does continental material get formed, clearly the process seems separate from the oceanic crust, and much slower. What consequence do you see in those processes and the comprehensiveness of marine fossil record?

1. The glacial polish and striations, and terminal moraines, were buried by other sediments, then eroded in places - "scraps" of glacial material exposed and uneroded. Glacial polish (Wegener "abraded basal surfaces") is a physical (and likely chemical as well) process that converts the top several millimeters of granite or other hard rock into a hard, shiny surface. Striations are when larger rocks in the underside of the glacier are physically dragged on this surface, and leave a mark like a stylus. (It "chatters" - drags get slightly deeper and then hops up; so the striation is rough in the direction of travel and smooth in the opposite direction). Glaciers / ice sheets act as a conveyor belt for rocks; these are dumped at the edge of the ice sheet, forming a terminal moraine. When the ice sheet is relatively stable (inputs snow - outputs melting) for a long time, the edge of the ice sheet remains at the same place and the terminal moraine gets very large, showing the extent of the ice sheet. Wegener did not observe any of this directly; he cites three geologists that did the actual fieldwork on (or pieced together on that continent) the Permian ice sheet, and Koken, the geologist that pieced together the fieldwork to produce the actual extent of the glacier. You can also get an idea of the uncertainty of the age; they are using relationship to coal beds and cosmopolitan (short-lived, widespread species) fossils to approximately date the ice sheet. It could also be argued that the glaciations are different ages and not a single ice sheet, especially to geologists that have not seen the original rocks. 

Quote from Wegener's 1912 lecture:

Quote

One of the strongest proofs of these ideas are to be found in Permian glaciation (some say Carboniferous), the traces of which have been observed at some places in the southern hemisphere, but are missing in the northern hemisphere. This Permian glaciation was the concern of palaeogeographers. These undoubted moraines on abraded basal surfaces are found in Australia8, South Africa9, South America10 and above all in east India.

Koken showed in a special treatment of this subject and on a map with the current distribution of land, that such a large extent of a polar ice cap is impossible. Even if one considers the South American discoveries uncertain, which is hardly possible anymore, and we place the pole in the best position namely in the middle of the Indian Ocean, the most distant inland ice is still 30–33° across. With a glaciation of this magnitude no part of the Earth’s surface would have been ice free. With such a south polar location, the north pole would fall in Mexico where no trace of Permian glaciation is found. The South American glacial outcrops would lie on the equator.

Image of (eroded) glacial polish with striations from Yosemite: (it is difficult to tell from a photograph, but I believe the ice was travelling from left to right across the picture based on several strong striations tapering off to the right as the "stylus" rock is eroded.) I picked this photograph because the resistance to erosion - large preserved area - of the glacial polish is apparent versus the uneven erosion of the granite below, and you can get an idea of the thickness of several millimeters even without explicit scale. I was interested in the physics and chemistry of glacial polish, which has never been well-worked out, but never had time to really dig into the problem.

Glacial-Polish-Yosemite-2902.jpg

 

2. Continental crust through time - placeholder

 

Edited by Grepley

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1 hour ago, Grepley said:

Image of (eroded) glacial polish with striations from Yosemite: (it is difficult to tell from a photograph, but I believe the ice was travelling from left to right across the picture based on several strong striations tapering off to the right as the "stylus" rock is eroded.) I picked this photograph because the resistance to erosion - large preserved area - of the glacial polish is apparent versus the uneven erosion of the granite below, and you can get an idea of the thickness of several millimeters even without explicit scale. I was interested in the physics and chemistry of glacial polish, which has never been well-worked out, but never had time to really dig into the problem.

That's so cool. Is there a change in the cristalline structure, or chemical composition, or both?

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2 hours ago, slade19 said:

Introduction to genetic analysis, by Griffiths, Wessler, Carroll and Doebley. It's a simple one that carries its own weight (meaning that they explain how DNA works in it, so no knowledge is presupposed), it covers a lot of fields of study in biology, it's very practical (it explains how the technology works, how the studies are carried out) and it's probably the most gratifying of the list since it can easily be followed and what is presented can be conceptually used readily.

This sounds the most interesting to me and I can also find it most easily. I would say 300 pages.

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Posted (edited)

IMG_3156_polish_striations-1024x768.jpg

http://www.kochanski.org/kelly/yosemite-sparkles/

 The glacier polish remnants are interesting. Was this gathered from a receding glacier or an area known to hold a glacier previous along that path(your picture from left to right) This would indicate a directional movement of the glacier,yes? Would be nice to have an aerial view to see the pathway.....also existing glacier should show some evidence of this as that glacier recedes currently?

Quote

Glaciers’ traces are visible everywhere in the Sierras. Many scientists have painstakingly cataloged them: glacial polish; deep U-shaped valleys; erratic boulders and moraines (the last two are are carried miles by the ice and dropped on seemingly random plains and hilltops). The first of these was John Muir (c1865), who spent years walking the mountains and demonstrating that Yosemite Valley was once covered in ice. Article above.

Also the complexity of what is going on with earth is truly amazing.

Current_complexity_node_full_image_2.jpg

Credit: ESA > Space in Images > 2015 > 06 > Current complexity

 
 
...... added to this post 28 minutes later:
 
Quote

The field is particularly weak over the South Atlantic Ocean – known as the South Atlantic Anomaly. This weak field has indirectly caused many temporary satellite ‘hiccups’ (called Single Event Upsets) as the satellites are exposed to strong radiation over this area. 

Was your attention drawn to South Atlantic Anomaly for the following reason in quote?

Edited by PlatoHagel

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On 1/9/2017 at 11:34 AM, slade19 said:

That's so cool. Is there a change in the cristalline structure, or chemical composition, or both?

Geomorphologists only care for glacial polish as a marker of glacial activity, and hold that it is all physical, like polishing a mirror. Looking at it edge on, whether in the field or cutting a chunk in half to really see the texture, using a 15x field lens, I think there is chemical remodelling as well. The ice is in direct contact with the bed, so there is likely not much addition of ions from water at the bed of warm glaciers, and it is very cold so reactions would go slowly - so I hypothesize it would be dissolution and deposition of silica forming a hard cement. (There is little weathering of flour-sized particles at the glacier bed, even taking up ions. Thus the load of ions in the water is small in any case to form new minerals, and this also shows that chemical reactions are definitely retarded). I had a glacially polished rock I was planning to cut up for optical mineralogy thin sections and perhaps electron microprobe work (X-ray backscatter for compositions), but never had time to get around to making the thin sections etc. This was in the granodiorite (just a little more Fe, Mg, Ca than granite proper) from Yosemite. Looking at polish over basalt, which has relatively low silica, looks much more like a physical polishing phenomenon - though I have not been to Devil's Postpile, the best place for looking at glacial polish over basalt columns (columns formed from cooling joints, sand inbetween dropped by glaciers):

14562381-basalt-column-ends-smoothed-by-

 
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21 hours ago, PlatoHagel said:

IMG_3156_polish_striations-1024x768.jpg

http://www.kochanski.org/kelly/yosemite-sparkles/

 The glacier polish remnants are interesting. Was this gathered from a receding glacier or an area known to hold a glacier previous along that path(your picture from left to right) This would indicate a directional movement of the glacier,yes? Would be nice to have an aerial view to see the pathway.....also existing glacier should show some evidence of this as that glacier recedes currently?

Yosemite was a warm valley glacier. (You also get movement in ice sheets at the edges that are like warm valley glaciers - ice streams. These can travel quite far, for example two ice streams covered most of Minnesota and one traveled down to Iowa from the Canadian Shield ice cap during the previous Ice Ages.) Glaciers are fed on the upper part with inputs of snow, which turn to ice. Ice is a non-Newtonian fluid that actually flows - there are many complex processes going on, and it is highly temperature dependent, but a reasonable rule of thumb is that velocity is correlated with H^4 in a warm valley glacier, which is everywhere near the melting point of water - so a thin sheet of ice does not flow, but the thicker it is, the faster it flows. Ice flow is driven by the slope of the top of the glacier, so it can go over large "bumps" in the topography at the base. This is what is happening in the picture - the ice is flowing from bottom left, where the person is standing, to the crest of the hill in the upper right. The other process that happens under a warm valley glacier is sliding due to a thin lubrication of water - usually one surge that happens in the spring when the majority of meltwater is, well, melting. This sliding of the ice causes grinding against the bedrock, in particular where the glacier is flat or moving uphill at the base (where it is moving downhill it often gets separated from the bed and filled with water). 

Velocity profile in a valley glacier: this is why it forms U-shaped valleys! (The first picture is a good 3D cutaway, but the second shows the velocity profiles in a glacier much better). 
slide_5.jpg

3602479_orig.jpg?448

 

Accumulation zone / movement / melting. If you drop a rock at the head of a glacier, it will eventually melt out at the foot of the glacier. The lines inside the glacier show the trace of what would happen to a rock that is in the ice. In the accumulation zone, above the snowline where snow does not melt annually, rocks get continually buried. In the ablation / melting zone, where ice is melted every year, rocks melt out of the ice. (As implied, the ends of a glacier can get covered with rock, which complicates the melting dynamics - single rocks will heat up and increase melting, a thick layer of rocks retards melting and shields the end of the glacier so that it can extend farther.) The glacial ice acts as a huge conveyor belt, and most of the rocks melt out at the end (toe) of the glacier, resulting in a ring of rocks called a terminal moraine (when the glacier is at steady-state with accumulation and ablation / melting) - the dark speckles in the ice at the end represent rocks, and the dark shadow at the end is a terminal morraine. You can see that the ice surface slopes downward, while it can travel over large (and small!) changes in topography at the base. It acts very differently than water / streams!
1299837_dyn.gif

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Spoiler
21 hours ago, PlatoHagel said:

 

Quote

Also the complexity of what is going on with earth is truly amazing.

Current_complexity_node_full_image_2.jpg

Credit: ESA > Space in Images > 2015 > 06 > Current complexity

 

 

 

 

Fortunately we are dealing with comogenic particles (greater than 10 Gev) rather than solar wind particles (~1 kev) - so it makes calculations much easier, since the particles are many orders of magnitude more energetic. Cosmogenic particles are streaming throughout the galaxy, superaccelerated by supernovae explosions; the density and flux can be taken as constant. They are the source of most of our natural radiation. About half of the shielding at sea level is from the magnetic field (factor of two between the equator and the poles; shielding mostly constant between the equator and 60 degrees latitude, drops sharply to half the shielding above 60 degrees latitude). The other half is provided by the atmosphere; if you are at sea level, half the shielding is from the total thickness of the atmosphere above you. The atmospheric depth for the lowest five kilometers can be approximately modeled as exponentially decreasing, with a length scale of 1.6 km. So people that live in Los Alamos have about twice the radiation per year that I do, but it is all natural and has to do with living at a high altitude, while I live near sea level. Note that one also gets a healthy dose of radiation from flying in an aeroplane. 

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21 hours ago, PlatoHagel said:
 
 
Quote

The field is particularly weak over the South Atlantic Ocean – known as the South Atlantic Anomaly. This weak field has indirectly caused many temporary satellite ‘hiccups’ (called Single Event Upsets) as the satellites are exposed to strong radiation over this area. 

Was your attention drawn to South Atlantic Anomaly for the following reason in quote?

Not particularly concerned. The magnetic field is not a pure dipole, and is best modeled with a weak quadrapole moment (and even on to the octapole and 16-pole moments). The magnetic high over China and low in the south Atlantic have been there since I was a wee little undergraduate, a couple decades ago, so again they are not changing much at the moment. If the quadrapole moments (and higher moments) started getting a lot stronger, and the dipole moment weakened, that would be the time to start being concerned. So again, not much change. (Look at the "chaos" of the magnetic field during a magnetic reversal in the Glatzmeir model in the original post, in the blue and yellow - practically no dipole moment, and it is all "chaos" in octopole / 16-pole / higher moments.)

Edited by Grepley

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On 1/9/2017 at 9:36 AM, slade19 said:

The Cell, by Cooper and Hausman, Excellent book detailing the various processes and mechanisms that allow life to function in the first place. I preferred this one to a more thorough Molecular biology of the cell to avoid overloading with molecular details of pathways and their proteins, which would be excessive for a first time.

^1st choice, especially after learning this is the best one of the five to lead to Neurosciences

 

On 1/9/2017 at 9:36 AM, slade19 said:

Campbell's Biology, it's a big one, but it's a classic and very wide in scope, which will allow the readers to form a solid big picture view of biology for subsequent reading. It's not very detailed however, it's an overview, and since it's a big one, we will have to select chapters anyway as a minimum reading.

^2nd choice, seems a good place to start and a good reference investment.

 

[I know we are doing unranked choice this time, but I thought that I would annotate and rank them for other people selecting book(s)]. 

I would be willing to read 300 focused pages (e.g. from The Cell) or 500 more basic pages (Campbell's Biology or Harper's Illustrated Biochemisty). 

Edited by Grepley

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If anyone is willing to read the book for March, it might be a good idea to vote quickly so that we may choose the book, and those who need to get it can get it. We will have to know in a week (21th). Since there is no obligation to read it, you don't have to be committed to reading all of it to vote.

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On 1/9/2017 at 0:36 PM, slade19 said:

Also, to start organizing the book reading for March, I have selected 5 books up for voting (then, if the book is too big, a vote will be carried out to select the chapters that all will read):

[...]

1. Introduction to Immunology

2. The Cell

3. Neurosciences

4. Illustrated Biochem.

5. Intro. to Genetic Analysis

6. Dev. Bio.

7. Campbell's

 

Edited by Suraj

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This week, I am putting forward 5 pages by Watson and Crick detailing the first accurate structure of DNA, and a discussion of the biological significance their model had in genetic inheritance.

https://tetrad.ucsf.edu/sites/tetrad.ucsf.edu/files/media/Watson and Crick- Molecular Structure of Nucleic Acids (1953) Nature 171- 737-738..pdf

https://tetrad.ucsf.edu/sites/tetrad.ucsf.edu/files/media/Watson and Crick- Genetical Implications of the Structure of Deoxyribonucleic Acid (1953) Nature 171- 964-967..pdf

There are other unrelated articles on the side because that's a scan of the 1953 Nature issue.

Some observations on the significance of their work: most of the groundwork had already been done, it had been close to a hundred years since Miescher first isolated DNA, we already knew the chemical composition (nucleotides, made of a sugar, a phosphate, and a purine or pyrimidine), and we already knew how they joined together (so we knew they formed strands=polynucleotides thanks to Levene) and we had a series of observations (Chargaff's rules) detailing some constants like ratios of A/T and G/C very close to unity. We also, as you may read, already knew it was forming a helix, but not the details.

We had also figured out the genetic nature of DNA (that it was the support to heredity) just 10 years prior. You should know that for a very long time, DNA was considered boring and having a mere structural role in the cell. That was due to the high amount of fast-moving research on proteins, their catalytic abilities, and their chemical versatility (so we thought they held the genetic information since they were so versatile and complex) while DNA was an extremely monotonous compound, so difficult to work on precisely, and held to contain little to no information (how could such a dull molecule hold the key to such complexity). It required different techniques of investigation and information theory to figure out that may not be the case.
We may go back to the 1944 paper that proved DNA to be the support of heredity later.

So what Watson and Crick put together, was just a synthesis of all the previous work and getting their hands on the cleanest X-ray diffraction pattern of DNA by Rosalind Franklin and Wilkins to figure out it was a double-helix and not a triple helix like most models at the time. They also used a recent development in model building by Pauling (they were even afraid Pauling might get to their conclusions before them) that allowed them to predict the structure from angles and distances between atoms.

And that's how they came to their final prediction detailing the structure of B-DNA (the major form of DNA, in addition there is A-DNA, Z-DNA, and B'-DNA). They also gave an account of how information is then encoded and replicated, and how mutations may arise (by incorporating tautomeric forms of bases that can bind to the wrong base, therefor corrupting the information) which, in a large sense, is true. They made a mistake by forgetting about a hydrogen bond between G and C which is physiologically important in gene regulation using the GC box, and correctly figured out that methylated cytosine is equivalent to regular cytosine information wise (genetically that is, epigenetically, it's another story). Finally, We now know that triplexes and quadruplexes of DNA can exist in cells, and can have some function, so three strand models were not false in essence, just not molecularly accurate (as far as I know).

 
 
...... added to this post 33 minutes later:
 

Oh, almost forgot, they say ribonucletide (RNA) can't form a double helix, but that is only true of the B-form, RNA can form a double helix of the A-form.

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Some additional information:

More and more people now know about Rosalind Franklin and her work. What they are usually told is that she made the picture of the DNA crystal that confirmed W&C's model, but what actually happened is she figured out that the way we extracted DNA before was putting it in a mix of the A and B form while crystallography of viruses gave different results because it was moist, so she prepared a way to isolate and analyze the B form specifically since it's the main one in biological systems and then took the right pure pictures that unlocked everything (how it organized into crystals=how the strands looped around eachothers, that the phosphates are on the outside, and a few other crucial development). She was extremely close to cracking the structure but she was a perfectionist, and tried to analyze everything mathematically, while W&C were amateur chemists, extracted the main insights (believed it was a helix without a doubt) and tinkered with a cardboard model until it fit.

She died before the Nobel prize was awarded to W, C, and her collaborator, Wilkins.

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just an interesting (well, to me) extra for anyone that pertains to point 1, i've read everything linked and a little bit more.

http://www.environmentandsociety.org/exhibitions/wegener-diaries/greenland-diaries

the originals are linked to within the parent link: http://www.environmentandsociety.org/exhibitions/wegener-diaries/original-document

i was curious about whether there would be a difference in the anomalies with the amount the magnetization changed (increased/reversed, etc.) by the sheer volume of vertical mass or if it was more influenced by the metal makeup and if would change by location (antarctica to ocean floor at the point of a reversal to giant's causeway). i don't completely understand everything, i don't think i'll be able to, and there's so much more to read than i thought there would be.

anyways, i've been having a lot of fun reading up, thanks for hosting this topic @Grepley

 

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The result of the vote is The Cell with four voices. We will be discussing it at the beginning of March. Tomorrow I will tell you the chapters that are the most interesting to read so that those who can't read it in full may prioritize a subset. Or we can leave it up to a vote, but I am not sure it would be practical.

The paper of next week (so starting tomorrow) is up for public suggestion.

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Ok, looking at the chapters, and considering that the main interest people had was in having an introduction to Neurosciences, here is a selection of those that would be preferable to read:

1,2,3,4 is the introduction, and explains how we even arrive at this knowledge, what we study and the techniques we use; it also includes a reminder of molecular biology, very succinct; it's about 150 pages long.

5,6,7,8 details how DNA, RNA, and proteins are handled throughout a cell's life, it can be substituted by the posts in my old thread (biology crash course and news) which are denser and include less details, so reading them is not necessary if you are short on time. They add up to 200 pages.

10, 12, 13, 15 are the advanced ones, that will be necessary to go through Neurosciences. They add up to 180 pages.

So you can read the whole 750 pages (which I can only recommend), or the full preparation at 530 pages, or the light version at 330 pages.

I will perhaps update, as I read through, what turned out to be necessary or what ended up useless, but I am confident it's not going to change.

 

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@slade19 - Is the 6th Edition of The Cell acceptable? It is available used for about $10 plus shipping. The 7th Edition is closer to $100 used.

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Yes, I actually think that's the version I have at my disposall. If I find the 7th edition, I will look for what's different and tell you if it's really important.

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