LDG et son origine

Bonsoir

Voilá un article fort interessant sor l'origine du LDG

En anglais, pourtant

http://phys.org/news/2013-10-evidence-comet-earth.html

Vous pouvez toujours utiliser Googletranslate

Saludos

Sanscelerien

Cela me semble dès plus plausible. On peut se demander ce qui se passerait si une comète exploserait au dessus de terre agricoles. De la formation de "trinitite non radioactive" ou de gros bloc de fulgurites

Un texte glané dans la grande www:

Unique chemistry of a diamond-bearing pebble from the Libyan Desert Glass strewnfield, SW Egypt: Evidence for a shocked comet fragment
Publication date: 15 November 2013
Source: Earth and Planetary Science Letters, Volume 382

Author(s): Jan D. Kramers , Marco A.G. Andreoli , Maria Atanasova , Georgy A. Belyanin , David L. Block , Chris Franklyn , Chris Harris , Mpho Lekgoathi , Charles S. Montross , Tshepo Ntsoane , Vittoria Pischedda , Patience Segonyane , K.S. (Fanus) Viljoen , Johan E. Westraadt

We have studied a small, very unusual stone, here named “Hypatia”, found in the area of southwest Egypt where an extreme surface heating event produced the Libyan Desert Glass 28.5 million years ago. It is angular, black, shiny, extremely hard and intensely fractured. We report on exploratory work including X-ray diffraction, Raman spectroscopy, transmission electron microscopy, scanning electron microscopy with EDS analysis, deuteron nuclear reaction analysis, C-isotope and noble gas analyses. Carbon is the dominant element in Hypatia, with heterogeneous O/C and N/C ratios ranging from 0.3 to 0.5 and from 0.007 to 0.02, respectively. The major cations of silicates add up to less than 5%. The stone consists chiefly of apparently amorphous, but very hard carbonaceous matter, in which patches of sub- μ m diamonds occur. δ 13 C values (ca. 0‰) exclude an origin from shocked terrestrial coal or any variety of terrestrial diamond. They are also higher than the values for carbonaceous chondrites but fall within the wide range for interplanetary dust particles and comet 81P/Wild2 dust. In step heating, 40 Ar/ 36 Ar ratios vary from 40 to the air value (298), interpreted as a variable mixture of extraterrestrial and atmospheric Ar. Isotope data of Ne, Kr and Xe reveal the exotic noble gas components G and P 3 that are normally hosted in presolar SiC and nanodiamonds, while the most common trapped noble gas component of chondritic meteorites, Q , appears to be absent. An origin remote from the asteroid belt can account for these features. We propose that the Hypatia stone is a remnant of a cometary nucleus fragment that impacted after incorporating gases from the atmosphere. Its co-occurrence with Libyan Desert Glass suggests that this fragment could have been part of a bolide that broke up and exploded in the airburst that formed the Glass. Its extraordinary preservation would be due to its shock-transformation into a weathering-resistant assemblage.

Amusez-vous
Saludos

SAnscelerien

Darkangel a écrit:

Cela me semble dès plus plausible. On peut se demander ce qui se passerait si une comète exploserait au dessus de terre agricoles. De la formation de "trinitite non radioactive" ou de gros bloc de fulgurites

Bonjour,

Il y a un oui mais...
L'explosion d'une comète ,s'il elle a eu lieu, n'a pas du être au dessus de zone désertique de sable
Je comprenais la vitrification du sable, jusqu'à la découverte d'un outil en verre (biface), qui m'a fait prendre conscience que nos ancêtres ont travaillé le LDG .
Mais ces gens là ne vivaient pas dans les déserts , mais au contraire dans des zones riches en gibier, en eau , etc. 

J' en ai parlé donc à quelqu'un qui a étudié ce verre et qui m'a expliqué qu'en fait c'est la nature du sous-sol qui a donné le verre , car effectivement au dessus c'était la vie ...

Voilà, une petite rectification d'un "pas savant du tout"

A+
Daniel