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Sunday, 14 April 2013

Scientific note on the Lake House Meteorite


 A thin section (greatly enlarged) of a sample from the Lake House meteorite. Image:  Salisbury and South Wilts Museum, Salisbury

This is a useful note:
http://www.lpi.usra.edu/meetings/metsoc2011/pdf/5326.pdf
 It appears that the C14 age noted (around 10,000 yrs BP) is not an actual C14 age determination on organic material, but a weathering age determined by one of the cosmogenic dating techniques and calibrated to the radiocarbon age scale.

Where does the date of >30,000 yrs BP come from regarding the date of arrival on Planet Earth?  There has clearly been some oxygen isotope work, as suggested here:  "In fact, oxygen isotope evidence demonstrates that the meteorite had been weathered in a cold climate. It was also covered in fragments of the local chalk country rock. There now seems little doubt that the specimen is a genuine British “find” and may have been transported to the Salisbury area by glaciers, in a similar way to that proposed for the rocks used to construct nearby Stonehenge."

This too:  "Starting in the asteroid belt, it reached Earth at least 10,000 years ago, landing in a frozen, unknown northern wasteland. It was then transported south by a glacier, deposited on Salisbury Plain and probably used to build a tomb by Iron Age man. It was then dug up by a gentleman archaeologist and, for perhaps a century or so, rested near the doorstep of the Lake House mansion."

http://www.open.ac.uk/blogs/meteorite/?p=1540

I suppose this dating study is published somewhere -- still searching.......

======================

THE METEORITE FROM LAKE HOUSE

C.T. Pillinger, J.M. Pillinger, R.C. Greenwood, D. Johnson, A.G. Tindle, A.J.T. Jull and M. Ashcroft.

Contact:   c.t.pillinger@open.ac.uk

Introduction:
In 1991 a very big meteorite (>60kg, dimensions: diameter 50cm x height 40cm) was brought to the Natural History Museum by the then occupier of Lake House, a country mansion in Wiltshire, UK, associated with a large estate of the same name. The circumstances concerning the likely origins of this ‘find’ are dealt with in a companion abstract [1]. Our attention was attracted to it because of its proximity to Danebury Hill (20 km east), where the only British meteorite ‘find’, collected
under controlled circumstances, was located in 1974 [2]. If the large meteorite from Lake House turned out to be paired with the much smaller Danebury find, then the mystery surrounding its origin would be instantly solved.

The sample from Lake House was confirmed as a meteorite by Robert Hutchison [3] and subsequently returned to its owners. Our electron microprobe data from a PTS made from a chip taken at the OU suggest it should be classified as type H5 similar to our assignment for Danebury.

Petrography:
The sample is a heavily weathered (W5) [4], moderately shocked (S4) [5], equilibrated ordinary chondrite (H5). Distinct chondrules are present, but these tend to have poorly defined boundaries. Porphyritic types predominate, but barred olivine and radial pyroxene textured chondrules are also common. Chondrule mesostasis is recrystallised, with grain sizes generally below 50μm.  The sample is cut by a network of veins, up to 2 mm thick, filled with secondary weathering products.

Discussion
In respect of weathering characteristics, the two specimens are entirely different – areas in our Danebury PTS are grade W1 and the whole specimen is no worse than W2, whereas the meteorite from Lake House is W5. The thin section of the latter was made from a near surface chip of the highly corroded sample; the Danebury analyses were performed using a fresh interior portion. Not wishing to have what appeared to be a very delicate specimen disintegrate, we attempted to extract an interior core from the larger meteorite using an experimental drill being developed for robotic space missions. Much to our surprise prolonged drilling was unable to penetrate more than a millimeter into a location where the crust appeared to be absent. In earlier performance tests the drill had no difficulty in obtaining 1.5 cm long cores from basalt and concrete. We conclude that the inte-
rior of the meteorite from Lake House may not be as weathered as it appears from the outside.
Because we had obtained a very precise terrestrial weathering age for Danebury, samples of
the meteorite from Lake House were removed for Accelerator Mass Spectrometry terrestrial residence dating. The first sample studied has a 14C weathering age of 10,600 +/- 1800 years BP. A second run with a better specimen gave 9500 +/- 560 years. The large meteorite is clearly not
related to the small one authenticated from the archeological site a few kilometers away. Given that it is a single stone, the meteorite represents an unusually large ordinary chondrite find.

References:
[1] C.T.Pillinger and J.M.
Pillinger, this vol. [2] C.T.Pillinger et al., this vol. [3] pers. comm. [4] Wlotzka F. 1993
Meteoritics 28:460. [5] Stöffler D. et al. 1991. GCA 55:3845-3867.

Note:  W5 on the weathering scale is defined as: beginning alteration of mafic silicates, mainly along cracks.

30 comments:

GCU:Intwominds said...

So not the same meteorite but two different ones I thought that to be correct.
Just leaves those dusk-inducing druids wading through snow drifts to deposit micro-wanderers with care.
Oh for a pound for every meteorite and meteorite story I had to disabuse. (my favourite was the 'it burned the bed one!!). It was a bit of 19th cent glass slag.
M

Anonymous said...

https://fbcdn-sphotos-g-a.akamaihd.net/hphotos-ak-ash3/559489_10151514988553022_419258203_n.jpg

I found this near the Sanctuary at Avebury.
An animal had excavated out a lot of material from the center of a barrow including two types of pottery, a polished bone pin and several strange types of stone. I left them there.
PeteG

Anonymous said...

Ice age druids. Oh for a pound for every misplaced druid historical story I had to disabuse.

GCU:Intwominds said...

Quite!!
But we soldier nobly on.
I am dislexic did you say you have abused driuds (sic) in a burning bed?
Shame on you but shows you have quite catholic tastes.
M

BRIAN JOHN said...

That looks really interesting, Pete. Looks like a meteorite to me -- or a bit of one. Any other opinions?

GCU:Intwominds said...

At the risk of being slagged off by anon the sample looks anthropogenic to me.
I am not certain that many meteorites show a vesicular outer skin.
Does look post-industrial revolution to me but as Dr ixer always says macroscopical id of rocks is a mug's game from photos doubly so.
M

Anon, (do find a nom-de-spume!)Carravagio's models were they putti in his hands?

TonyH said...

Gordon Sumner, alias Sting, lives occasionally at Lake House as its owner. Talk of druids and driuds etc makes me recall that this same Sting gave permission for an excavation of an IRON AGE ( and thus at least the right time zone for Druids) burial within the grounds of Lake House some time in the 1990's. Written up in WANHS Wiltshire Studies magazine.No meteorite fragments as far as I know.

TonyH said...

I expect many of us know Danebury Hill Fort was excavated by the notable archaeologist Barry Cunliffe over a long period of time. Do others know about how "his" meteorite came to be found, and precisely where?

GCU.Intwominds said...

I thought in a grain pit so secure context.
M

Dave Maynard said...

There is quite a bit of information from googling 'Danebury + Meteorite' including this: http://www.lpi.usra.edu/meetings/metsoc2011/pdf/5321.pdf

Opinions seem to vary about whether the meteorite fell by itself into the storage pit, or was seen, collected and placed in the pit. I wonder whether it just happened to be on the hill and got casually incorporated in the spoil filling the pit at the end of its use.

The article above talks about C14 weathering dating giving a date at the time that Danebury hillfort was at its busiest. I don't know anything about this technique of dating meteorites. This result either shows the technique is very accurate, with confirmation coming from its location in a securely dated deposit, possibly an almost unique set of circumstances. The Lake House meteorite could be similar in being incorporated in a datable deposit.

The other option is that the technique is only dating the considerable activity occurring in the area at the time.

This interpretation assumes the meteorite fell generations before, lay unnoticed on the hill (it only weighs 30g) until being incorporated in an Iron Age deposit, acquiring all its dating attributes from the mess of an Iron Age hillfort with an economy based on arable and cattle rearing.

Dave

BRIAN JOHN said...

Dave -- we have to be careful about some of these dates. I wish there were some better scientific papers about them -- but at present all we seem to have are a few comments to the media or bits of "pop science" which don't give us any detail. What we seem to have is cosmogenic dating of various sorts, with some of the dates calibrated onto a C14 scale -- that does not mean that actual organic carbon has been measured.

Dave Maynard said...

I agree. I've never heard of this technique and don't see how, or where the content that is being dated is derived.

Constantinos Ragazas said...

Brian et al,

Why is the “Lake House” called the Lake House? Is there a lake where the Lake House is? And where about relative to Stonehenge is this Lake House? And if there is a lake where the Lake House is, could we speculate this lake at the Lake House was a much bigger lake millenniums ago? Could it have been a glacial lake created by meltwater during the great meltdown? Possibly an offspring of a Salisbury Lake I've been arguing existed?

It gets curiouser and curiouser each page!

Kostas

TonyH said...

Dave
haven't yet looked at the article you tell us about, and am just wondering if Prof Barrie Cunliffe [incidentally a leading light in knowledge of prehistoric activities along the western seaboard of Britain, Ireland, the Iberian Peninsula etc] has made any personal remarks about the provenance of the meteorite dicovered at Danebury, beyond saying it was in a grain pit.

Visited Danebury with an archaeological society from Bath when in my youth over 40 years ago and Barry spoke to us all.

TonyH said...

Kostas

You will find Lake House on the "Salisbury & Stonehenge" Ordnance Survey 1:25000 Explorer map. It may possibly take its name from the Lake Barrows, 2 kilometres south - west of Stonehenge, and the house also lies in the historic parish of Wilsford - cum - Lake. There is also a hamlet called Lake with a dry valley nearby called Lake Bottom.

Dave Maynard said...

Tony,

From my quick trawl of the internet, the meteorite was recognised many years after the excavation of the pit. Peter Salter was working through all the metal slags recovered from the site, maybe by sieving, and saw that this was rather different.

Thinking over this today, I can't really see it more than as a chance discovery that happened to end up in the pit, the only human interaction being that it was possibly some sort of curio.

You're making me all nostalgic, with the 40 years and Danebury. One of my first trips to a a pub was in Fordingbridge with some of Barry's diggers after a visit to Danebury. We were working on other excavations on the route of the M3 just north of Winchester, 1974 it must have been.

Dave

Constantinos Ragazas said...

Tony, thanks!

I am puzzled. Is there a British tradition of naming landmarks by names that do not describe the landmark?

How safe is it to assume these various places with “lake” in their name reflect folk memories of lakes in those places?

Kostas

BRIAN JOHN said...

Kostas -- remember that the English language is very old, and that many words have multiple meanings or changed meanings. In Pembrokeshire, where I live, the word "Lake" is often found in place names. It was often used for streams or rivers -- with no indication or suggestion of the former presence of large water bodies.

Constantinos Ragazas said...

Brian,

I well appreciate words have many meanings. The cause of many misunderstandings between us in the past.

What other meaning does “lake” have, if you know? And if a place with a creek is called “lake” when there was no lake at the place, why not call it “creek”? It is intriguing, don't you think, that many places are called “lake”?

Surely this is rooted in past folk memories. And if the collective memory has many places called “lake”, shouldn't that raise questions there were many small and big lakes in the area? And if there were many small and big lakes in an area, can we plausibly infer there was one very large lake in the area at one time?

If the collective memory remembers the many “lakes”, doesn't that argue these lakes existed not too far in the past? Say 2000 years in the past? That would date the “mother of all lakes” of an area to few millenniums. And this we may be able to calculate if we consider the topography and volume of a region and the drainage rate through some likely egress point.

Kostas

TonyH said...

"Nearby LAKE is derived from the Saxon word 'lacu' (small, often slow-moving stream)."

WILSFORD entry in "Wiltshire Place-Names: their Origin & Meaning, Martyn Whittock, 1997.

To illustrate how words change their meanings over time, the WILSFORD entry also states:-

HAM contains the Saxon word 'hamm' (land in a river bend).

Hmm................

From memory of my circumnavigatory days of the rural lanes of North Devon, Lake is also a topographical word there used for various streams.

Constantinos Ragazas said...

Tony,

I am convinced places change over time. But names for them remain the same. Thus, where once was a lake but later degraded to a stream the “lake” still names the place – now a “small, often slow-moving stream”. Any examples of lakes being called streams?

Does “hamlet” also derive from the same “land in a river bend”? Seems likely to me!

Kostas

chris johnson said...

Laku (lake) is one of the Proto Indo European (PIE) root words with the meaning of (water in) lake, pond, ditch, etc.

Had this word in SH context had a very ancient origin and mean what Kostas wants it to mean, then it might derive from other PIE roots such as eghero (inland lake) or even selos (sea, swamp).

Interesting too is the Middle English "laken" meaning to gift or to offer, as in to God. I like this connection in regard to Stonehenge.

I think Brian is right. We should not read too much into the naming of Lake House, etc, tempting though it is.

TonyH said...

When I was a little lad in Yorkshire, I'd ask my friends "are yer laking outside", meaning, "are you playing outside?"

This derives [from my memory] from the time of the Vikings. Our occasional contributor, Melvyn Bragg of Cumbria, has mentioned this same word from his own original roots - area too.

Then again, Brian mentions Greylake in Somerset in his "Stonehenge Enigma" work.

BRIAN JOHN said...

From my knowledge of Swedish I can tell you that "lek" means "to play." It's not pronounced as in "lake" -- but I can well imagine that in Yorkshire and the NE it might come out sounding the same!! So "leksak" is a toy, and "lekplats" is a playground. Nothing at all to do with water.

Constantinos Ragazas said...

Dear All,

“Lake” also is like “like”. The “Lake House” could derive from “(i) Like (the) House”. And “Lake Barrow” could mean “Like(able) Barrow”. While “Lake Bottom” becomes “Like (the) Bottom”. Brian's Sweetish “lek” for “play” completely answers Tony's laddish call to his friends.

So what! Any individual bit of evidence may have many separate explanations. It is never enough to 'convict'. But when the preponderance of the evidence all point to one theory being correct, fair-minded jurors must commit to it.

Any new thoughts how the “Lake House Meteorite” survived the earthly impact with land or ice? And still be round-shaped and relatively intact?

Note: The weathered surfaces of the Meteorite are very spherical while the more recently exposed surfaces suggest broken knock-offs. The surface cracks suggest rapid cooling and weathering.

Only if this Meteorite landed in deep water could it have survived and have the features it now has. And according to Prof. Pillinger, that happened around 30,000 BP. That it landed in water at that time fits Brian's contention this was an interglacial warm period.

I only have one question. Where did the Lake House Meteorite land? If it landed at Salisbury Plain (near where it was found) this would suggest Salisbury Plain was Salisbury Lake at the time it landed. And latter, during the deep freeze of the Younger Dryas some 10,000BP, this lake froze solid. Ergo my ice sheet cover of Salisbury Plain.

Any questions?

Kostas

TonyH said...

A possible good source (of information, not of water) to contact as to the earthly provenance of yonder Salisbury Museum meteorite would be Dr John Chandler, an eminent local historian. He was born, or grew up, in Amesbury, and used to be the Local Studies Librarian for Wiltshire, and a colleague of mine, before becoming a free-lance publisher and speaker. For those with eyes (and motivation) to see, look him up on the Internet. His books are published by Hob Nob Books, and no doubt he has an email address.

TonyH said...

Brian: I think we did pronounce "lekin'" with a short vowel, so, by George!, I think we're definitely on the right lines, don't yer know, so to speak. We did, however, always drop the "g" [as in occasional deceased contributor Philip Larkin', that one's for Myris' benefit].

GCU.intwominds said...

A hit a hit a palpable hit.
Super.
M

TonyH said...

I say, Myris, thank you, what a splendid chap, thank you old bean, what!

TonyH said...

A useful link to Edward Duke, the antiquarian of Lake House who is widely attributed with digging up the Lake House Meteorite, appears on the Modern Antiquarian website, at:-

http://www.the modernantiquarian.com/site/1796/lake_group.html

Other references are easily found via your Search Engine