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General => Science => Topic started by: Recusant on May 02, 2020, 08:30:19 PM

Title: Reports on the Annals of the Former World
Post by: Recusant on May 02, 2020, 08:30:19 PM
The title of this thread comes from the title of John McPhee's great book, Annals of the Former World (https://www.goodreads.com/book/show/78.Annals_of_the_Former_World). Though it examines the geology of North America, it's a superb description of the science of geology as well. It came to mind when I decided to make a thread for geology news. :)

Most recently, although already posted elsewhere:

"Japan Puts Its Mark on Geologic Time with the Chibanian Age" | Eos (https://eos.org/articles/japan-puts-its-mark-on-geologic-time-with-the-chibanian-age)

Now this:

"Ancient Australian Rocks Suggest Earth's Continents Were Shifting Earlier Than Thought" | ScienceAlert (https://www.sciencealert.com/ancient-australian-rocks-suggest-earth-s-continents-have-been-moving-for-over-3-billion-years)

QuoteEarth's continents are constantly on the move, it's a key feature of our planet, but that wasn't always the case.

While some scientists think Earth's tectonic plates began pushing and pulling only a billion years ago, others think the whole process started nearly four billion years ago, when our planet was but an infant.

That's quite the discrepancy, and as usual, general agreement lies somewhere in between. Today, it's commonly thought Earth's tectonic plates began moving around 2.8 billion years ago, when the interior of our planet was just the right temperature to allow for the formation of 15 rigid plates.

Even still, disagreement reigns. Direct evidence from this time is hard to come by, and now some of the oldest rocks on Earth suggest we may have been more than 400 million years off the mark.

Analysing magnetism in ancient rocks from Australia and South Africa, researchers at Harvard and MIT claim tectonic plates were moving at least 3.2 billion years ago and maybe earlier.

"Basically, this is one piece of geological evidence to extend the record of plate tectonics on Earth farther back in Earth history," says (https://www.eurekalert.org/pub_releases/2020-04/hu-tps042020.php) Alec Brenner, who researches paleomagnetics at Harvard University.

"Based on the evidence we found, it looks like plate tectonics is a much more likely process to have occurred on the early Earth and that argues for an Earth that looks a lot more similar to today's than a lot of people think."

The Pilbara craton (https://en.wikipedia.org/wiki/Pilbara_Craton) in Western Australia is one of the oldest slices of Earth's ancient crust and contains fossils for some of the earliest organisms (https://www.sciencealert.com/those-3-5-billion-year-old-fossils-in-australian-rocks-really-are-fossils-new-study-finds) on our planet. Stretching nearly 500 kilometres across (300 miles), this chunk of primordial crust was formed as early as 3.5 billion years ago.

Drilling into a portion of this craton, known as the Honeyeater Basalt, researchers used state of the art magnetometers and demagnetising equipment to uncover the region's magnetic history.

Roughly 3.2 billion years ago, their data reveals a shift from one point to another, a latitudinal drift of 2.5 centimetres a year.

Or, as the authors put it (https://advances.sciencemag.org/content/6/17/eaaz8670), "a velocity comparable with those of modern plates."

[Continues . . . (https://www.sciencealert.com/ancient-australian-rocks-suggest-earth-s-continents-have-been-moving-for-over-3-billion-years)]

The paper is linked in the final paragraph above.
Title: Re: Reports on the Annals of the Former World
Post by: Tank on May 06, 2020, 06:37:52 AM
I missed this! I have to say that with my layman's understanding of plate tectonics (Dunning Krugar warning) that I would have thought that when the Earth was younger and hotter plate tectonics would have been more active than now.
Title: Re: Reports on the Annals of the Former World
Post by: Recusant on May 15, 2020, 05:57:16 AM
Quote from: Tank on May 06, 2020, 06:37:52 AM
I missed this! I have to say that with my layman's understanding of plate tectonics (Dunning Krugar warning) that I would have thought that when the Earth was younger and hotter plate tectonics would have been more active than now.

That seems reasonable to me as well. I'm not privy to the line of thinking which would make it likely that there was a more recent (in geological time) start to tectonic movement in the Earth's crust.
Title: Re: Reports on the Annals of the Former World
Post by: Recusant on May 15, 2020, 06:04:23 AM
New hypothesis on the Great Uncomformity (https://en.wikipedia.org/wiki/Great_Unconformity#Powell%E2%80%99s_Unconformity,_Grand_Canyon) of the Grand Canyon and similar uncomformities around the world.

"A billion years missing from geologic record: Where it may have gone" | ScienceDaily (https://www.sciencedaily.com/releases/2020/05/200507130704.htm)

QuoteThe geologic record is exactly that: a record. The strata of rock tell scientists about past environments, much like pages in an encyclopedia. Except this reference book has more pages missing than it has remaining. So geologists are tasked not only with understanding what is there, but also with figuring out what's not, and where it went.

One omission in particular has puzzled scientists for well over a century. First noticed by John Wesley Powell in 1869 in the layers of the Grand Canyon, the Great Unconformity, as it's known, accounts for more than one billion years of missing rock in certain places.

Scientists have developed several hypotheses to explain how, and when, this staggering amount of material may have been eroded. Now, UC Santa Barbara geologist Francis Macdonald and his colleagues at the University of Colorado, Boulder and at Colorado College believe they may have ruled out one of the more popular of these. Their study appears in the Proceedings of the National Academy of Sciences.

"There are unconformities all through the rock record," explained Macdonald, a professor in the Department of Earth Science. "Unconformities are just gaps in time within the rock record. This one's called the Great Unconformity because it was thought to be a particularly large gap, maybe a global gap."

A leading thought is that glaciers scoured away kilometers of rock around 720 to 635 million years ago, during a time known as Snowball Earth, when the planet was completely covered by ice. This hypothesis even has the benefit of helping to explain the rapid emergence of complex organisms shortly thereafter, in the Cambrian explosion, since all this eroded material could have seeded the oceans with tremendous amounts of nutrients.

Macdonald was skeptical of this reasoning. Although analogues of the Great Unconformity appear throughout the world -- with similar amounts of rock missing from similar stretches of time -- they don't line up perfectly. This casts doubt as to whether they were truly eroded by a global event like Snowball Earth.

[. . .]

"The basic hypothesis is that this large-scale erosion was driven by the formation and separation of supercontinents," Macdonald said.

The Earth's cycle of supercontinent formation and separation uplifts and erodes incredible extents of rock over long periods of time. And because supercontinent processes, by definition, involve a lot of land, their effects can appear fairly synchronous across the geologic record.

However, these processes don't happen simultaneously, as they would in a global event like Snowball Earth. "It's a messy process," Macdonald said. "There are differences, and now we have the ability to perhaps resolve those differences and pull that record out."

[Continues . . . (https://www.sciencedaily.com/releases/2020/05/200507130704.htm)]
Title: Re: Reports on the Annals of the Former World
Post by: Recusant on May 16, 2020, 04:12:37 AM
Trying to understand a place where our ancestors used to live. Though I think this one may be under deeper water, the story below reminded me of Doggerland (https://en.wikipedia.org/wiki/Doggerland). It's an impressive effort. These scientists appear confident in their modelling, and perhaps the confidence is justified.

"Early humans thrived in this drowned South African landscape" | ScienceDaily (https://www.sciencedaily.com/releases/2020/05/200515131917.htm)

(https://i.imgur.com/AR1s0r4.png)
The southern tip of Africa. Dotted line offshore shows the extent of the Paleo-Agulhas Plain during the last glacial maximum.
Image Credit: J. Sealy et al. / Quaternary Science Reviews

QuoteScientists have reconstructed the paleoecology the Paleo-Agulhas Plain, a now-drowned landscape on the southern tip of Africa that was high and dry during glacial phases of the last 2 million years and may have been instrumental in shaping the evolution of early modern humans.

Early humans lived in South African river valleys with deep, fertile soils filled with grasslands, floodplains, woodlands, and wetlands that abounded with hippos, zebras, antelopes, and many other animals, some extinct for millennia.

In contrast to ice age environments elsewhere on Earth, it was a lush environment with a mild climate that disappeared under rising sea levels around 11,500 years ago.

An interdisciplinary, international team of scientists has now brought this pleasant cradle of humankind back to life in a special collection of articles that reconstruct the paleoecology of the Paleo-Agulhas Plain, a now-drowned landscape on the southern tip of Africa that was high and dry during glacial phases of the last 2 million years.

"These Pleistocene glacial periods would have presented a very different resource landscape for early modern human hunter-gatherers than the landscape found in modern Cape coastal lowlands, and may have been instrumental in shaping the evolution of early modern humans," said Janet Franklin, a distinguished professor of biogeography in the department of Botany and Plant Sciences at UC Riverside, an associate member of the African Centre for Coastal Palaeoscience at Nelson Mandela University in South Africa, and co-author of several of the papers.

Some of the oldest anatomically modern human bones and artifacts have been found in cliff caves along the coast of South Africa. For many years, the lack of shellfish in some layers at these sites puzzled archaeologists. In spite of apparently living near the ocean, the inhabitants hunted mostly big game -- the sort of animals that typically live farther inland.

Scientists knew a submerged landscape existed on the continental shelf just offshore, but it wasn't until recently, perhaps inspired by rising sea levels of our current human-caused global warming, they realized these caves might have made up the westernmost edge of a long-lost plain.

During most of the Pleistocene, the geological era before the one we live in now, these caves were not located on the coast. With so much of the Earth's water locked up in continent-sized glaciers, sea level was much lower, and humans could have thrived between the cliffs and a gentler coastline miles and miles to the east.

A special issue of Quaternary Science Reviews presents papers using a wide range of techniques to reconstruct the environment and ecology of the Paleo-Agulhas Plain. They reveal a verdant world rich with game, plant, and coastal resources, periodically cut off from the mainland during warm spells between glacial periods when sea level rose to levels similar to those of today, which would have played an important role in human evolution.

[Continues . . . (https://www.sciencedaily.com/releases/2020/05/200515131917.htm)]

Two of the papers are open access (https://www.sciencedirect.com/journal/quaternary-science-reviews/vol/235/suppl/C).
Title: Re: Reports on the Annals of the Former World
Post by: Tank on May 16, 2020, 06:12:39 AM
Oh for a time machine :(
Title: Re: Reports on the Annals of the Former World
Post by: Recusant on May 22, 2020, 04:53:37 AM
Well, this one is about something that's going on right now. It's on the wandering north magnetic pole, which has been moving more quickly of late.

Out of curiosity, I checked on what the south magnetic pole is doing, and though it does wander, it hasn't been exhibiting the same changes. Moreover, the south magnetic pole is much further from the geographical south pole than the north magnetic pole is from the geographical north pole. ("Wandering of the Geomagnetic poles" | NOAA National Centers for Environmental Information (https://www.ngdc.noaa.gov/geomag/GeomagneticPoles.shtml))

Back to the real purpose of this post:

"Earth's Magnetic North Is Moving From Canada to Russia, And We May Finally Know Why" | ScienceAlert (https://www.sciencealert.com/russia-is-stealing-magnetic-north-from-canada-and-this-could-be-what-s-behind-it)

QuoteOur planet wears its magnetic field like an oversized coat that just won't sit comfortably. All that sliding means the north magnetic pole is destined to move ever closer to Siberia's coastline over the coming decade.

There's no conspiracy behind it - but the geological forces responsible have been something of a mystery. Now, we might be a little closer to understanding what's going on.

Researchers from the University of Leeds in the UK and the Technical University of Denmark have analysed 20 years of satellite data, finding that a monolithic competition between two lobes of differing magnetic force near the core is likely to be behind the pole's wanderlust.   

When the precise position of Earth's magnetic north was located for the first time back in 1831, it was squarely in Canada's corner of the Arctic, on the Boothia Peninsula in the territory of Nunavut.

Ever since, fresh sets of measurements have recorded this spot drift north by an average of around 15 kilometres (about 9 miles) every year.

Advanced technology means we can now keep a careful watch on the pole's location with unprecedented accuracy. Prior to the 1970s, the north magnetic pole's position was like a drunken stagger. Since then, it's had a mission, marching in a straight line, building speed.

Since the 1990s, its movement has quadrupled in speed, to a current rate of between 50 and 60 kilometres (about 30 and 37 miles) a year. In late 2017, the pole's sprint brought it within 390 kilometres (240 miles) of the geographical north pole.

[Continues . . . (https://www.sciencealert.com/russia-is-stealing-magnetic-north-from-canada-and-this-could-be-what-s-behind-it)]
Title: Re: Reports on the Annals of the Former World
Post by: Randy on May 22, 2020, 03:30:34 PM
Quote from: Tank on May 16, 2020, 06:12:39 AM
Oh for a time machine :(

Billy Rubin's wife might be able to make one out of zip ties.
Title: Re: Reports on the Annals of the Former World
Post by: billy rubin on May 22, 2020, 07:54:22 PM
and push pins
Title: Re: Reports on the Annals of the Former World
Post by: hermes2015 on May 23, 2020, 06:22:36 AM
I've been to a large nature reserve in that beautiful area. There is an air monitoring lab with gas chromatographs, and I went there once to train them to measure SF6 (sulphur hexafluoride) in the atmosphere. Air samples are drawn in from a tall tower and fed into a gas sampling loop in the GC for measurement.

https://www.google.com/search?sxsrf=ALeKk02rVpGd6WAY8WCF-saBXbnUNFOi0A:1590211412880&source=univ&tbm=isch&q=nature+reserve+southern+tip+of+africa&sa=X&ved=2ahUKEwi_p4eTn8npAhWEyKQKHW0eDdYQ7Al6BAgKEC4&biw=1876&bih=936
Title: Re: Reports on the Annals of the Former World
Post by: Icarus on May 24, 2020, 12:57:15 AM
Holy cow Hermes!  That link is spectacular.  Not so much about the chemistry but about the whole bit of beautiful SA information.

Most of we dullard Americans envision Africa as a place where Hutus and Tutsi kill each other.  I know better but your link has made me think of that continent in a different way.

As a matter of fact an Amrerican doctor lives across the street from me. He got some of his Med education in SA. His wife is a very charming South African woman who is entirely civilized and sophisticated.

A Brit friend who was here for a while once, when in a philosophic and wine fueled discussion, said this to me: "Americans are so insular".  That statement stuck in my brain to this day. He was polite enough not to tell me that a lot of Americans are ill informed clods. He was correct of course.
Title: Re: Reports on the Annals of the Former World
Post by: Dark Lightning on May 24, 2020, 04:07:46 AM
Quote from: Icarus on May 24, 2020, 12:57:15 AM
Holy cow Hermes!  That link is spectacular.  Not so much about the chemistry but about the whole bit of beautiful SA information.

Most of we dullard Americans envision Africa as a place where Hutus and Tutsi kill each other.  I know better but your link has made me think of that continent in a different way.

As a matter of fact an Amrerican doctor lives across the street from me. He got some of his Med education in SA. His wife is a very charming South African woman who is entirely civilized and sophisticated.

A Brit friend who was here for a while once, when in a philosophic and wine fueled discussion, said this to me: "Americans are so insular".  That statement stuck in my brain to this day. He was polite enough not to tell me that a lot of Americans are ill informed clods. He was correct of course.

"Insular"? The rest of the world's people only have to look at the kind of people who voted for the chump to see that (among other indicators). It is a huge portion of the US' population, sad to say. I also will observe that people who have to live "up against" other people who have vastly different political opinions, like in Europe, reduces that insular behavior.
Title: Re: Reports on the Annals of the Former World
Post by: Icarus on May 24, 2020, 10:13:55 PM
That word, insular, was to imply that we see our country as an island of brilliant, productive, inspired, and generally better than the rest of the world.   We are on a really big island, separated from a lot of other countries by large oceans. Our AMERICA IS NUMBER ONE mind set misses the mark of course, but it works for a lot of us.   
Title: Re: Reports on the Annals of the Former World
Post by: Randy on May 25, 2020, 01:21:30 AM
That was one of the things I liked about working in an office. I usually ended up meeting someone from out of the country. I also got to travel to the UK a few times and work with my team. I'd learn a lot about how the USA is viewed. Many were engaged talking to me and having me explain a few things. I also lived in Germany for three years when I was in elementary school.

I traveled to the Philippines for two weeks once and got to enjoy the customs and the dialog we'd share, including getting completely drunk off a $1.00 bottle of rum made there. I was the only one of the group who didn't have a hangover which surprised me.

I met a doctor who believed in ghosts for instance and quite a few believe that witchcraft is real.

But I'm digressing and I didn't mean to hijack the thread. What I wanted to get to is that so many never travel abroad and talk to the natives. There is so much to be gained by sitting at the dinner table and talking.
Title: Re: Reports on the Annals of the Former World
Post by: Dark Lightning on May 25, 2020, 01:29:42 AM
Quote from: Icarus on May 24, 2020, 10:13:55 PM
That word, insular, was to imply that we see our country as an island of brilliant, productive, inspired, and generally better than the rest of the world.   We are on a really big island, separated from a lot of other countries by large oceans. Our AMERICA IS NUMBER ONE mind set misses the mark of course, but it works for a lot of us.   

I understand that. :smilenod: What I like about this country is when I worked as an engineer and we had people from all over the world working in cooperation. They know how it can be elsewhere, from the outside, and really lied living in the US. Melting pot, for sure. I worked with a lot of US citizens who were only in it for themselves. Really disappointing. Those "Dark Personalities", as discussed in another thread.
Title: Re: Reports on the Annals of the Former World
Post by: Recusant on May 25, 2020, 05:16:11 AM
Quote from: Randy on May 25, 2020, 01:21:30 AMThat was one of the things I liked about working in an office. I usually ended up meeting someone from out of the country. I also got to travel to the UK a few times and work with my team. I'd learn a lot about how the USA is viewed. Many were engaged talking to me and having me explain a few things. I also lived in Germany for three years when I was in elementary school.

I traveled to the Philippines for two weeks once and got to enjoy the customs and the dialog we'd share, including getting completely drunk off a $1.00 bottle of rum made there. I was the only one of the group who didn't have a hangover which surprised me.

I met a doctor who believed in ghosts for instance and quite a few believe that witchcraft is real.

But I'm digressing and I didn't mean to hijack the thread. What I wanted to get to is that so many never travel abroad and talk to the natives. There is so much to be gained by sitting at the dinner table and talking.

It ain't digression, it's discussion. Tangled tangents are part of any genuine discussion. :spaghetti:

Or at least that's how we roll here. 

As for travel, not everybody in the US has a good opportunity to travel. Maybe they'll visit Canada or go to a resort in Mexico if the fancy strikes them. Some get to take a cruise later in their lives, but that's not the same thing at all.

If they're not in the military or working for an international corporation, the cost of living abroad for any length of time is prohibitive. A one or two week tour (preferably not as part of a package holiday) can definitely give a taste of the different perspective. If the person is receptive to that.
Title: Re: Reports on the Annals of the Former World
Post by: Recusant on May 28, 2020, 10:08:33 PM
Continuing on the geomagnetic front (gotta love those pop science headline editors  ::)):

"The Mysterious Anomaly Weakening Earth's Magnetic Field Seems to Be Splitting" | ScienceAlert (https://www.sciencealert.com/mysterious-anomaly-weakening-earth-s-magnetic-field-seems-to-be-splitting-into-two)

QuoteNew satellite data from the European Space Agency (ESA) reveal that the mysterious anomaly weakening Earth's magnetic field continues to evolve, with the most recent observations showing we could soon be dealing with more than one of these strange phenomena.

The South Atlantic Anomaly is a vast expanse of reduced magnetic intensity in Earth's magnetic field, extending all the way from South America to southwest Africa.

Since our planet's magnetic field acts as a kind of shield – protecting Earth from solar winds and cosmic radiation, in addition to determining the location of the magnetic poles – any reduction in its strength is an important event we need to monitor closely, as these changes could ultimately have significant implications for our planet.

At present, there's nothing to be alarmed about. The ESA notes that the most significant effects right now are largely limited to technical malfunctions on board satellites and spacecraft, which can be exposed to a greater amount of charged particles in low-Earth orbit as they pass through the South Atlantic Anomaly in the skies above South America and the South Atlantic Ocean.

[Continues . . . (https://www.sciencealert.com/mysterious-anomaly-weakening-earth-s-magnetic-field-seems-to-be-splitting-into-two)]
Title: Re: Reports on the Annals of the Former World
Post by: Dark Lightning on May 28, 2020, 10:58:17 PM
Freaky. No magnetic field is bad news for a lot of the inhabitants of this place, as stated in the article.
Title: Re: Reports on the Annals of the Former World
Post by: Randy on May 28, 2020, 11:28:02 PM
Quote from: Dark Lightning on May 28, 2020, 10:58:17 PM
Freaky. No magnetic field is bad news for a lot of the inhabitants of this place, as stated in the article.

Think of all the compass makers going out of business!
Title: Re: Reports on the Annals of the Former World
Post by: Dark Lightning on May 29, 2020, 12:09:44 AM
Quote from: Randy on May 28, 2020, 11:28:02 PM
Quote from: Dark Lightning on May 28, 2020, 10:58:17 PM
Freaky. No magnetic field is bad news for a lot of the inhabitants of this place, as stated in the article.

Think of all the compass makers going out of business!

I'm reminded of a physics lab I was conducting in the mid-90s. One pair of guys couldn't get their compass to act like it should, and I couldn't figure it out, either. I got them new equipment and moved them to another part of the room, where the thing worked properly. The following summer while inventorying the contents of the cabinets I discovered an immensely powerful magnet in the cabinet below where those two boys were working. Should have looked there that day, but I had enough going on and didn't think of it. I incorporated that into my next set of lectures on magnetostatics. If one put a steel plate on one pole, it took nearly all one's hand strength to pull it off, and if it slipped, blood blisters would ensue. I'm not sure what/where it came from.
Title: Re: Reports on the Annals of the Former World
Post by: Randy on May 29, 2020, 01:01:39 AM
An immensely powerful magnet and no idea where it came from? One would think that someone would be looking for it. When you left the physics lab for the final time did you take the magnet with you?
Title: Re: Reports on the Annals of the Former World
Post by: Dark Lightning on May 29, 2020, 02:22:09 AM
Quote from: Randy on May 29, 2020, 01:01:39 AM
An immensely powerful magnet and no idea where it came from? One would think that someone would be looking for it. When you left the physics lab for the final time did you take the magnet with you?

Oooooh, I was sorely tempted, believe me! I was told by one of the more experienced teachers that it came from a cyclotron, but those are all electromagnets. This piqued my interest, so I went and looked for different types of magnets. Either I was misinformed or misremembered what I was told (after all, it was ca '96), but it would appear that it came from a magnetron-

https://en.wikipedia.org/wiki/Horseshoe_magnet#/media/File:Magnetron_magnet.JPG (https://en.wikipedia.org/wiki/Horseshoe_magnet#/media/File:Magnetron_magnet.JPG)

Though the one the school had was a bit larger. And HELLA strong.
Title: Re: Reports on the Annals of the Former World
Post by: Recusant on June 10, 2020, 01:14:07 AM
I've been watching Nick Zentner's geology talks on YouTube for a while now. Recently I watched the one on supervolcanoes (https://www.youtube.com/watch?v=NcreTTI9Rew). Zentner talked about the Yellowstone hotspot of course, and showed its historic path, leaving large (approximately 30 miles/48 kilometres diameter) calderas behind as it migrated east and a bit north to its present location. Or more precisely, as the continent migrated west and a bit south over the hotspot. (He also took a moment to debunk the "Yellowstone may be getting ready to erupt!!!" headlines that pop up every once in a while.) A new paper discusses two of these ancient calderas, and what they can tell us about the hotspot under Yellowstone.

"Discovery of ancient super-eruptions indicates the Yellowstone hotspot may be waning" | ScienceDaily (https://www.sciencedaily.com/releases/2020/06/200603132516.htm)

QuoteThroughout Earth's long history, volcanic super-eruptions have been some of the most extreme events ever to affect our planet's rugged surface. Surprisingly, even though these explosions eject enormous volumes of material -- at least 1,000 times more than the 1980 eruption of Mount St. Helens -- and have the potential to alter the planet's climate, relatively few have been documented in the geologic record.

Now, in a study published in Geology, researchers have announced the discovery of two newly identified super-eruptions associated with the Yellowstone hotspot track, including what they believe was the volcanic province's largest and most cataclysmic event. The results indicate the hotspot, which today fuels the famous geysers, mudpots, and fumaroles in Yellowstone National Park, may be waning in intensity.

The team used a combination of techniques, including bulk chemistry, magnetic data, and radio-isotopic dates, to correlate volcanic deposits scattered across tens of thousands of square kilometers. "We discovered that deposits previously believed to belong to multiple, smaller eruptions were in fact colossal sheets of volcanic material from two previously unknown super-eruptions at about 9.0 and 8.7 million years ago," says Thomas Knott, a volcanologist at the University of Leicester and the paper's lead author.

"The younger of the two, the Grey's Landing super-eruption, is now the largest recorded event of the entire Snake-River-Yellowstone volcanic province," says Knott. Based on the most recent collations of super-eruption sizes, he adds, "It is one of the top five eruptions of all time."

[. . .]

Both of the newly discovered super-eruptions occurred during the Miocene, the interval of geologic time spanning 23-5.3 million years ago. "These two new eruptions bring the total number of recorded Miocene super-eruptions at the Yellowstone-Snake River volcanic province to six," says Knott. This means that the recurrence rate of Yellowstone hotspot super-eruptions during the Miocene was, on average, once every 500,000 years.

By comparison, Knott says, two super-eruptions have -- so far -- taken place in what is now Yellowstone National Park during the past three million years. "It therefore seems that the Yellowstone hotspot has experienced a three-fold decrease in its capacity to produce super-eruption events," says Knott. "This is a very significant decline."

These findings, says Knott, have little bearing on assessing the risk of another super-eruption occurring today in Yellowstone. "We have demonstrated that the recurrence rate of Yellowstone super-eruptions appears to be once every 1.5 million years," he says. "The last super-eruption there was 630,000 years ago, suggesting we may have up to 900,000 years before another eruption of this scale occurs." But this estimate, Knott hastens to add, is far from exact, and he emphasizes that continuous monitoring in the region, which is being conducted by the U.S. Geological Survey, "is a must" and that warnings of any uptick in activity would be issued well in advance.

[Continues . . . (https://www.sciencedaily.com/releases/2020/06/200603132516.htm)]
Title: Re: Reports on the Annals of the Former World
Post by: Dark Lightning on June 10, 2020, 01:45:03 AM
900kY?  :haironfire:

Guess I'll be dead.  :clapping:

Personally, since I retired and my daily commute is a bit less than the 94-mile round trip on the freeways (58 miles of it on the San Diego Fwy), my expectation of death is greatly reduced.

I like reading the stuff you post, Recusant. Sometimes I stumble on it myself, but it's still cool.
Title: Re: Reports on the Annals of the Former World
Post by: Randy on June 10, 2020, 02:37:50 AM
I was planning to stick around for another 900,000 years but now I'm not so sure.
Title: Re: Reports on the Annals of the Former World
Post by: Recusant on June 10, 2020, 03:00:32 AM
Quote from: Dark Lightning on June 10, 2020, 01:45:03 AM
900kY?  :haironfire:

Guess I'll be dead.  :clapping:

Personally, since I retired and my daily commute is a bit less than the 94-mile round trip on the freeways (58 miles of it on the San Diego Fwy), my expectation of death is greatly reduced.

I like reading the stuff you post, Recusant. Sometimes I stumble on it myself, but it's still cool.

:boaterhat: It's my pleasure.

For any non-geologist with an interest in geology, Zentner's work is worth checking out. A superb geology teacher giving talks for the general public. He's mostly discussing the Pacific Northwest of North America and surrounding regions, but he does a fine job of covering the fundamentals of geology as well as specialized geological topics in an engaging way.

Title: Re: Reports on the Annals of the Former World
Post by: Dark Lightning on June 10, 2020, 05:34:23 AM
Quote from: Randy on June 10, 2020, 02:37:50 AM
I was planning to stick around for another 900,000 years but now I'm not so sure.

[clearing throat for loud proclamation...harrumph!] Accept the lard hey-Seuss cristoball as your personal savior and you will live forever!  ;D Damn, I would not want to live forever.
Title: Re: Reports on the Annals of the Former World
Post by: Randy on June 10, 2020, 02:28:49 PM
Nah, eternity sounds boring. Besides, worshiping for eternity does not seem like paradise to me.
Title: Re: Reports on the Annals of the Former World
Post by: Recusant on June 25, 2021, 06:00:03 AM
A nice long cycle. If our species is still around when the next peak arrives in 20 million years or so, they'll see some interesting times.

"The Earth has a pulse -- a 27.5-million-year cycle of geological activity" | EurekAlert (https://www.eurekalert.org/pub_releases/2021-06/nyu-teh061821.php)

QuoteGeologic activity on Earth appears to follow a 27.5-million-year cycle, giving the planet a "pulse," according to a new study published in the journal Geoscience Frontiers.

"Many geologists believe that geological events are random over time. But our study provides statistical evidence for a common cycle, suggesting that these geologic events are correlated and not random," said Michael Rampino, a geologist and professor in New York University's Department of Biology, as well as the study's lead author.

Over the past five decades, researchers have proposed cycles of major geological events--including volcanic activity and mass extinctions on land and sea--ranging from roughly 26 to 36 million years. But early work on these correlations in the geological record was hampered by limitations in the age-dating of geologic events, which prevented scientists from conducting quantitative investigations.

However, there have been significant improvements in radio-isotopic dating techniques and changes in the geologic timescale, leading to new data on the timing of past events. Using the latest age-dating data available, Rampino and his colleagues compiled updated records of major geological events over the last 260 million years and conducted new analyses.

[Continues . . . (https://www.eurekalert.org/pub_releases/2021-06/nyu-teh061821.php)]

The paper appears to be open access:

"A pulse of the Earth: A 27.5-Myr underlying cycle in coordinated geological events over the last 260 Myr" | Geoscience Frontiers (https://www.sciencedirect.com/science/article/pii/S1674987121001092)

QuoteAbstract:

We performed spectral analyses on the ages of 89 well-dated major geological events of the last 260 Myr from the recent geologic literature. These events include times of marine and non-marine extinctions, major ocean-anoxic events, continental flood-basalt eruptions, sea-level fluctuations, global pulses of intraplate magmatism, and times of changes in seafloor-spreading rates and plate reorganizations.

The aggregate of all 89 events shows ten clusters in the last 260 Myr, spaced at an average interval of ~ 26.9 Myr, and Fourier analysis of the data yields a spectral peak at 27.5 Myr at the ≥ 96% confidence level. A shorter period of ~ 8.9 Myr may also be significant in modulating the timing of geologic events.

Our results suggest that global geologic events are generally correlated, and seem to come in pulses with an underlying ~ 27.5-Myr cycle. These cyclic pulses of tectonics and climate change may be the result of geophysical processes related to the dynamics of plate tectonics and mantle plumes, or might alternatively be paced by astronomical cycles associated with the Earth's motions in the Solar System and the Galaxy.

[¶ added. - R]



Title: Re: Reports on the Annals of the Former World
Post by: Tank on June 25, 2021, 09:20:54 AM
I read about this a few days ago in context of the magnetic pole switching.
Title: Re: Reports on the Annals of the Former World
Post by: Recusant on July 04, 2021, 07:51:38 AM
Quote from: Randy on June 10, 2020, 02:28:49 PM
Nah, eternity sounds boring. Besides, worshiping for eternity does not seem like paradise to me.

The atheist in a foxhole certain to be over-run by a merciless foe. I salute him, and should have done when he wrote that post.  Really we are all in a similar situation, though the circumstances may be less certainly imminent. Regrets abound; we abide, for now.  :smokin cool:
Title: Re: Reports on the Annals of the Former World
Post by: Recusant on November 15, 2021, 08:39:40 AM
Sticking their nasty rock hammers in where they don't belong! Everybody knows the Grand Canyon was formed during the time of Noahz Flud.   :pedant:

Yes, it's from this past summer, but in a geological sense that was a couple of nanoseconds ago.  :eh:

"Geologists dig into Grand Canyon's mysterious gap in time" | EurekAlert (https://www.eurekalert.org/news-releases/925959)

QuoteA new study led by the University of Colorado Boulder reveals the complex history behind one of the Grand Canyon's most well-known geologic features: A mysterious and missing gap of time in the canyon's rock record that covers hundreds of millions of years.

The research comes closer to solving a puzzle, called the "Great Unconformity (https://www.colorado.edu/today/2020/04/27/GreatUnconformity)," that has perplexed geologists since it was first described nearly 150 years ago.

Think of the red bluffs and cliffs of the Grand Canyon as Earth's history textbook, explained Barra Peak, lead author of the new study and a graduate student in geological sciences at CU Boulder. If you scale down the canyon's rock faces, you can jump back almost 2 billion years into the planet's past. But that textbook is also missing pages: In some areas, more than 1 billion years' worth of rocks have disappeared from the Grand Canyon without a trace.

Geologists want to know why.

"The Great Unconformity is one of the first well-documented geologic features in North America," Peak said. "But until recently, we didn't have a lot of constraints on when or how it occurred."

Now, she and her colleagues think they may be narrowing in on an answer in a paper published this month in the journal Geology. The team reports that a series of small yet violent faulting events may have rocked the region during the breakup of an ancient supercontinent called Rodinia. The resulting havoc likely tore up the earth around the canyon, causing rocks and sediment to wash away and into the ocean.

[Continues . . . (https://www.eurekalert.org/news-releases/925959)]

The paper is open access. A PDF of it is available by clicking through from the link below.

"Zircon (U-Th)/He thermochronology reveals pre-Great Unconformity paleotopography in the Grand Canyon region, USA" | Geology (https://pubs.geoscienceworld.org/gsa/geology/article/doi/10.1130/G49116.1/606722/Zircon-U-Th-He-thermochronology-reveals-pre-Great)

QuoteAbstract:

The Great Unconformity is an iconic geologic feature that coincides with an enigmatic period of Earth's history that spans the assembly and breakup of the supercontinent Rodinia and the Snowball Earth glaciations. We use zircon (U-Th)/He thermochronology (ZHe) to explore the erosion history below the Great Unconformity at its classic Grand Canyon locality in Arizona, United States. ZHe dates are as old as 809 ± 25 Ma with data patterns that differ across both long (∼100 km) and short (tens of kilometers) spatial wavelengths.

The spatially variable thermal histories implied by these data are best explained by Proterozoic syndepositional normal faulting that induced differences in exhumation and burial across the region. The data, geologic relationships, and thermal history models suggest Neoproterozoic rock exhumation and the presence of a basement paleo high at the present-day Lower Granite Gorge synchronous with Grand Canyon Supergroup deposition at the present-day Upper Granite Gorge.

The paleo high created a topographic barrier that may have limited deposition to restricted marine or nonmarine conditions. This paleotopographic evolution reflects protracted, multiphase tectonic activity during Rodinia assembly and breakup that induced multiple events that formed unconformities over hundreds of millions of years, all with claim to the title of a "Great Unconformity."

[¶ added. - R]
Title: Re: Reports on the Annals of the Former World
Post by: Recusant on December 02, 2022, 05:56:57 AM
From whence the highly addictive element oxygen in the atmosphere of our Earth? With a special guest appearance by that particularly interesting crystal, zircon.

"Where did the Earth's oxygen come from? New study hints at an unexpected source" | The Conversation (https://theconversation.com/where-did-the-earths-oxygen-come-from-new-study-hints-at-an-unexpected-source-191673)

QuoteThe amount of oxygen in the Earth's atmosphere makes it a habitable planet.

Twenty-one per cent of the atmosphere consists of this life-giving element. But in the deep past — as far back as the Neoarchean era 2.8 to 2.5 billion years ago — this oxygen was almost absent.

So, how did Earth's atmosphere become oxygenated?

Our research, published in Nature Geoscience, adds a tantalizing new possibility: that at least some of the Earth's early oxygen came from a tectonic source via the movement and destruction of the Earth's crust.

The Archean eon represents one third of our planet's history, from 2.5 billion years ago to four billion years ago.

This alien Earth was a water-world, covered in green oceans, shrouded in a methane haze and completely lacking multi-cellular life. Another alien aspect of this world was the nature of its tectonic activity.

One feature of modern subduction zones is their association with oxidized magmas. These magmas are formed when oxidized sediments and bottom waters — cold, dense water near the ocean floor — are introduced into the Earth's mantle. This produces magmas with high oxygen and water contents.

On modern Earth, the dominant tectonic activity is called plate tectonics, where oceanic crust — the outermost layer of the Earth under the oceans — sinks into the Earth's mantle (the area between the Earth's crust and its core) at points of convergence called subduction zones. However, there is considerable debate over whether plate tectonics operated back in the Archean era.

Our research aimed to test whether the absence of oxidized materials in Archean bottom waters and sediments could prevent the formation of oxidized magmas. The identification of such magmas in Neoarchean magmatic rocks could provide evidence that subduction and plate tectonics occurred 2.7 billion years ago.

We collected samples of 2750- to 2670-million-year-old granitoid rocks from across the Abitibi-Wawa subprovince of the Superior Province — the largest preserved Archean continent stretching over 2000 km from Winnipeg, Manitoba to far-eastern Quebec. This allowed us to investigate the level of oxidation of magmas generated across the Neoarchean era.

Measuring the oxidation-state of these magmatic rocks — formed through the cooling and crystalization of magma or lava — is challenging. Post-crystallization events may have modified these rocks through later deformation, burial or heating.

So, we decided to look at the mineral apatite which is present in the zircon crystals in these rocks. Zircon crystals can withstand the intense temperatures and pressures of the post-crystallization events. They retain clues about the environments in which they were originally formed and provide precise ages for the rocks themselves.

Small apatite crystals that are less than 30 microns wide — the size of a human skin cell — are trapped in the zircon crystals. They contain sulfur. By measuring the amount of sulfur in apatite, we can establish whether the apatite grew from an oxidized magma.

[Continues . . . (https://theconversation.com/where-did-the-earths-oxygen-come-from-new-study-hints-at-an-unexpected-source-191673)]

The paper (https://www.nature.com/articles/s41561-022-01071-5) is behind a paywall.

QuoteAbstract:

Oxidized, sulfur-rich arc magmas are ubiquitous in modern subduction-zone environments. These magmas are thought to form when the fluids released during prograde metamorphism of subducting oceanic crust and overlying sediments oxidize and hydrate the asthenospheric mantle. In contrast, Archaean arc-type magmas are thought to be relatively reduced and sulfur poor, owing to the lower concentrations of marine sulfate and limited oxidative seafloor alteration in the anoxic ocean before the Great Oxidation Event some 2.4 billion years ago (Ga).

Here we measure the total sulfur concentration and relative abundances of S6+, S4+ and S2− in zircon-hosted apatite grains from sodic and potassic intrusive rocks from the ~2.7 Ga southeastern Superior Province, Canada. We find that, rather than being reduced and sulfur poor, the sulfur budget of the Neoarchaean magmas was dominated by S6+ and abruptly increased to concentrations comparable to Phanerozoic arc magmas following the interpreted onset of subduction at approximately 2.7 Ga, coincident with the first global pulse of crust generation. These findings indicate that oxidized, sulfur-rich magmas formed in subduction zones independent of ocean redox state and could have influenced oceanic–atmospheric and metallogenic evolution in the Neoarchaean.

Title: Re: Reports on the Annals of the Former World
Post by: Recusant on November 26, 2023, 05:58:56 AM
Seems entirely appropriate for this thread.  :sidesmile:

"Is some of the body that collided with Earth to form the Moon still recognisable inside our planet?" | The Conversation (https://theconversation.com/is-some-of-the-body-that-collided-with-earth-to-form-the-moon-still-recognisable-inside-our-planet-217031)

QuoteScientists have dated the birth of the Solar System to about 4.57 billion years ago. About 60 million years later a "giant impact" collision between the infant Earth and a Mars-sized body called Theia created the Moon.

Now, new research suggests that the remains of the large object that collided with the young Earth to form the Moon are still identifiable deep within the planet as two large lumps. These lumps make up about 8% of the volume of the Earth's mantle, which is the rocky zone between the Earth's iron core and its crust.

The new study, led by Qian Yuan of Arizona State University and Caltech, argues that the heat generated by this collision was not enough to melt the whole of the Earth's mantle, so the innermost mantle remained solid.

Consequently, the researchers say, the melted mantle of Theia didn't completely mix with Earth's mantle. That would have made the Theia remnants indistinguishable from Earth's mantle as a whole. Instead, a lot of Theia's mantle ended up as two continent-sized lumps that now sit on top of the Earth's core-mantle boundary.

[Continues . . . (https://theconversation.com/is-some-of-the-body-that-collided-with-earth-to-form-the-moon-still-recognisable-inside-our-planet-217031)]






The paper (https://www.nature.com/articles/s41586-023-06589-1) is behind a paywall.

QuoteAbstract:

Seismic images of Earth's interior have revealed two continent-sized anomalies with low seismic velocities, known as the large low-velocity provinces (LLVPs), in the lowermost mantle1. The LLVPs are often interpreted as intrinsically dense heterogeneities that are compositionally distinct from the surrounding mantle2.

Here we show that LLVPs may represent buried relics of Theia mantle material (TMM) that was preserved in proto-Earth's mantle after the Moon-forming giant impact3. Our canonical giant-impact simulations show that a fraction of Theia's mantle could have been delivered to proto-Earth's solid lower mantle.

We find that TMM is intrinsically 2.0–3.5% denser than proto-Earth's mantle based on models of Theia's mantle and the observed higher FeO content of the Moon. Our mantle convection models show that dense TMM blobs with a size of tens of kilometres after the impact can later sink and accumulate into LLVP-like thermochemical piles atop Earth's core and survive to the present day.

The LLVPs may, thus, be a natural consequence of the Moon-forming giant impact. Because giant impacts are common at the end stages of planet accretion, similar mantle heterogeneities caused by impacts may also exist in the interiors of other planetary bodies.