June ArXivery

Articles studied June 2022 - some of which might go to Slashdot.

Biological Homochirality

Other things happened.

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June science readings.

Maybe I'll get back to something "productive" now. I think Uncle Roger (deceased) would approve.

Biological Homochirality and the Search for Extraterrestrial Biosignatures

https://arxiv.org/pdf/2205.01193.pdf

Eny Fule Noe that the homochirality of biological molecules is a really important topic in O(s)OL studies. Homochirality is probably essential in biochemistry, because of the concentration problem -if you don't control chirality of reactions, then every chiral centre (which are inevitable in molecules above a fairly low complexity threashold) will approximately halve your reaction efficiency.

Is it important to biochemistry? Ask any thalidomide victim (the sedative is harmless ; flip one chiral centre and you get the teratogen.

Chirality is mentioned in almost every discussion of amino acids and proteins, because amino acids other than glycine (the simplest) has at least one chiral centre. It's also important in sugars, because most sugar monomers have one or two chiral centres, in addition to any introduced in the polytmerisation. Unsurprisingly, chirality is important to getting proteins to fold up into the "right" shape.

This paper examines evidence for homochiral enantiomeric excess (of L- over D, or of D- over L enantiomers) exists beyond Earth, elsewhere in the Solar system, in the "local neighbourhood" (galactic arm, galaxy group - what do they mean?) or in the wider universe.

This short (8 pages) paper seems to be an introduction or a summary for a forthcoming book on the subject, but the publication isn't named.

The big question is, would the detection of a robust homochirality signal by remote (spectroscopic, probably) means be a robust biosignature?

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Sector collapse

When we were doing the Vulcanology trip to Tenerife, a couple of the stops were to examine the faults bounding the Guimar (SE coast) and Santa Cruz (N coast) collapses. Always worth thinking about, even without the fears stirred up by that Portsmouth (?) hazard research centre.
Well, Prof Ceiling Cat Emeritus has been posting about his current jaunt around Hawai'i, and one look at the geography of Oahu made me think "sector collapse" again.

Oh dear, that's not good looking. That looks like lumps of islands 10km by 20km which have broken off and slid over 50km down the seabed slope.
What does the profile look like? (following the white line in the bathymetry plot)

10km NE-SW by 20km NW-SE by 1.5km thick. That's a big chunk of rock. The tsunami that hit the Pacific coasts (and particularly the British Columbia to Washington section) would have been ... unhealthy to see. I wonder what the date was.

For comparison, here's the most recent slump from the North side of Tenerife.

(250m bathymetry contours, bolded at 1000m intervals, for all images) The characteristic "lumps on the sea floor" of a slump can be seen. In the profile you can estimate the thickness of the largest lump, though this slump seems to have fragmented more than the Hawai'i example above.

 To a first approximation, say 5km by 3km by 0.25km. More detailed mapping with sonar shows that a lot of the seabed has rough areas which are interpreted as earlier generations of slump. Upwards of 20 slumps have been identified around the Canaries archipelago. 
Probably the most recent slump around Tenerife (unless it has "gone" while I'm typing) is from the side of the island facing Gran Canaria.

 The profile shows how steeply the islands drop off away from the volcanic centres.

Note the level of the inter-island gap - 2.5km below sea level - compared to the abyssal plain to the North at over 3.5km below sea level. There is around a kilometre of fill in this gap which hasn't accumulated to the North.

 Since the turn of the millennium there has been considerable speculation about the possibility of major landslides from the flanks of volcanic islands in general, and the Canary archipelago in particular. While concern about the particular claims concerning a West-flank collapse of La Palma have somewhat abated, there are certainly major landslip features around ocean islands. The recent (22 December 2018) flank collapse of Anak Krakatoa in the Indonesian archipelago killed over 400 people, making the point that these things do indeed happen.