Wednesday, April 17, 2019

Geosonnet 52



Peridotite, without the peridot
A paradox, clinopyroxenite
What metasomatized this mantle plot
Reacting mantle min’rals out of sight?
A garnet, like an elephant, forgets
No detail of its formative hot years
Included in its structure, tiny bits
Of felsic melt, the mantle’s frozen tears
A crustal rock’s subducted ‘till it melts
The rock’s identity is not air tight
Melanosome in metamorphic belts?
Or metasomatized old hartzburgite?
The isotopes of osmium declare
They’d solve this if they weren’t so very rare



Other geosonnets: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52




Monday, April 08, 2019

Preserved Lemmings

I don't know what the elimination of G+ is going to do to this lounge, but if there is an interruption, please note that several years ago, the National Library of Australia decided this blog was worth archiving. The government archive version is here:
http://nla.gov.au/nla.arc-126431
So now lemmings can lounge on both the north AND south sides of Lake Burley Griffin.

Thursday, March 21, 2019

Shameless self-promotion and self-organizing

I keep losing the link to the Supplementary Information from my Geology paper (summarized as Geosonnet 42), so I'm posting the direct link here, where I hopefully won't lose it.
http://www.geosociety.org/datarepository/2016/2016176.pdf
And before you tell me a better way to keep track of things in the digital age, GET OFF MY LAWN!

Monday, February 18, 2019

Geosonnet 51

When oxygen and oceans mixed worldwide

Out dropped the world’s first heavy metal band
With silica and iron side by side
This rocking BIF precipitate was grand.
But modern industry required more
Than hematite with intermingled chert
The silica component they abhor
Must be expunged by fluids which convert
The BIF into a high grade iron mine
A cooling basal fluid can’t displace
As much quartz gangue as pulsing solo brine
With carbonate fade in- not acid- bass.
When silica got kicked out of the band
The iron oxide satisfied demand.



Other geosonnets: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52

Saturday, February 09, 2019

Sierra Sequoias from space

I wrote last year about the big trees of the Sierra Nevada mountains in California. One if the things that interested me was the ability of the Sequoia and the Sugar Pine to grow side-by-side, despite having very similar survival strategies- namely grow taller than everything else and live long enough for fire to clear our the shade tolerant trees so that your seeds can germinate.

Of course, as anyone who spends time on the forest knows, despite these trees having similar niches, they look quite different. The both have large trunks often bare of branches for the first 100 feet, but their vegetation has different forms. The Sugar Pine has very long, straight lateral branches, like the spars of a ship, while the sequoia crowns are more rounded. And because these trees are very large, it turns out that you can easily distinguish them in Google Earth. Here is a screenshot of the same grove I wrote about last year:

You can clearly see the long lateral branches on the pines (which also have somewhat bluer foliage). The larger, yellower trees with very wide trunks and rounded foliage are the sequoias.

Unfortunately, the sugar pine is in decline in many areas of its range, Here is a picture of dying trees in the national forest just south of the park:
The most obvious thing here is that the Sugar Pines are mostly dead. But there are other differences. Unlike in the National Park, here you cannot see the ground- the trees are growing too close together. One critique of the Forest Service is that it as lagged behind the Park Service in the use of controlled burns and recurrent fires. While I don't have the fire history of this exact area, the much thicker understory could be the result of decades of fire suppression. And if those trees are sucking up all the water, perhaps that has stressed the pines.

Sunday, January 20, 2019

Book Review: William Shakespeare’s Star Wars


By Ian Doescher
This is a stage adaptation of the plot of the original Star Wars movie, written in Iambic pentameter. It’s not done too badly, with lots of actual famous Shakespeare lines sprinkled throughout. And it is a clever idea. However, the joke gets old quickly; I gave up before they even got to Tatooine.

Sunday, December 09, 2018

Book review: The Great Way


The Way into Chaos
The Way into Magic
The Way into Darkness
By Harry Connolly

The Great Way is an epic Fantasy Trilogy by Harry Connolly. As the first two books end in cliffhangers, and the narrative immediately picks up afterwards, it is useful to look at them as volumes of a single story as opposed to related independent books. Luckily, the story is very good.

The story opens in the capital of an empire similar to Imperial Rome. Unlike the Romans, however, the Perdaini empire has a caste of scholars, whose sorcerous power is derived from ‘gifts’ brought by God-like- or alien-like beings. Once a generation, these beings visit, and this time, the visit goes terribly wrong.

A plague of ravenous beasts descends on the capitol, slaying the emperor and ravaging the city. The crown prince and a small portion of his entourage escape, including the two very different POV characters:  The first is Tejohn. An aging war hero who won fame and renown hunting down rouge scholars and quelling rebellion, he is the Prince’s bodyguard. The second is Cazia Freewell. The teenage daughter of a rebellious lord, she is kept in the imperial court as a hostage, where she is raised in the imperial culture and is studying to be a scholar. Despite their differences and hatred of each other, the POV characters are united in their desire to preserve the empire and protect the Prince, and they soon split up to run separate quests for him. As the plague spreads and the story progresses, however, the goal slips from maintaining the empire, to survival, of the characters, of civilization, and even of humanity itself.

As a fantasy adventure, this is a fast-paced, hard-hitting, and creative story. And I recommend it on that basis alone. But there are additional attractions that the story has to people of science.

One of the main thematic arcs is the position of scholars in society, and how their knowledge and power is handled and feared by society. This is seen through the viewpoint of Cazia, as she grows up and sees the wider world beyond the palace where he has been imprisoned, and also by Tejohn, who confronts his scars from fighting rogue sorcerers as he comes to the realization that they are needed in the fight to save humanity. Of course, this tale of an ancient fantasy empire is told by a modern American writer, and is prescient for scholars in the here and now. This becomes most clear in the third book, where Cazia experiences what modern scientists refer to as Cosmic Vertigo:

“I can look into the world.” The words barely made any sense, and she was the one saying them. “I can look into the world and see its parts.”

Just as clearly, she sees the fear, greed, and cunning that the rest of society feels when they realize she- like modern atomic scientists- can see and do things outside of the ordinary experience of most humans living their day to day lives. As the story takes place in a collapsing civilization, this is all the more important for all of us to appreciate.


Saturday, December 08, 2018

The Greenland impact crater


This is a brief note on the recent Science Advances paper on the Hiawatha Impact crater, a large, recent crater which lies under the Hiawatha glacier in extreme northern Greenland.

In the past, I have bagged out impact crater scientists and being alarmist and even dangerous. However, this discovery is the real deal. Similarly, I have occasionally criticized the “glamour-mag” approach to scientific publication, but in this instance, a big splash is appropriate, because it is a big deal, and the evidence is overwhelming.

The short version: Ice penetrating radar and analysis of glacial outwash sand show a large (31km diameter), recent impact crater under a Greenland glacier, complete with central peak. The outwash shows shocked quartz, probable melt glass, and PGE anomalies consistent with an iron (or stony iron) impactor. This is not one of those ancient, deformed, maybe-if-you-squint-you-can-see-a-circle crators, this is in your face and completely obvious to anyone who has studied even a little geology.

Like many short format papers, a lot of the details are in the supplementary materials.  For example:
This is a recent discovery because of global warming! Prior to 2012, the outlet glacer emptied into a lake. It is only ni the last 6 years that it has retreated onto land, so that the sediment they sampled and found the shocked quartz, impact glass, etc in was only exposed from beneath the melting ice sheet a few years ago.
They are planning on running conventional gravity surveys to look for rebound, but because all the ice is melting, the melt signal dominates the GRACE gravity signature.
No known impact ejecta is known from any of the North Greenland ice cores, making the crater likely to be older than the oldest of them (about 100ka). Ice cores are regularly checked for volcanic debris, and it is unlikely that they would miss something this large and close (quick math suggests the ejecta volume should be about 200-600 km3, making it a medium to large VEI-7 equivalent).

The crater overprints pre-glacial river valleys, and this is (as the authors state) probably Pleistocene in age (10ka-2.5Ma).

The melt glass should be datable via Ar/Ar dating, but it is not clear if they have recovered a large enough volume of the material to date at this stage.

I would expect a tektite field from an impact this size, but it isn’t clear where those tektites would end up. If they fell on ice (By definition, the Arctic was mostly ice-covered during most of the Pleistocene), then they would get carried to a moraine (on land), or float around until the ice was exported through the Fram Strait and melted somewhere in the NE Atlantic Ocean.

There is a controversial Younger Dryas impact hypothesis, which basically calls for an Arctic impactor as a trigger for the Younger Dryas cooling and extinction of the Clovis culture in North America. I would be careful connecting this crater to that event, as the NEEM ice core, less than 400km away, doesn’t have any reported ejecta, as known tephra are mostly basaltic. 

Finally, they report carbon in the silicate impact melt. That seems odd to me, as neither crustal gneisses nor iron meteorites have much carbon.  they should do ion probe d13C to get the isotopic composition. Who knows, maybe the impactor hit a peat bog.