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The Sahara's Abrupt Desertification
by Wal Thornhill

Part I

The following item was sent to me by a friend and member of the Canberra Astronomical Society. Of particular interest are the "abrupt" climate changes that are attributed to that arm waving catch-all beloved of climatologists, the unquantifiable "feedback" mechanisms in our weather systems. The suggested change of about 0.5 degree in the Earth's axial tilt seems ludicrously small to bring about the changes noted.

The switch from precipitation and moderate temperatures to aridity and high temperatures sounds very much like an episode of Earth's relocation in the solar system to an orbit closer to the Sun. That is a simple cause and effect relationship. Unfortunately for the climatologists, the rules of their game don't allow it at present.

I would like to know where all of the sand came from, too.

Wal Thornhill

American Geophysical Union Public Information Office 2000 Florida Avenue, NW Washington, D.C. 20009

(For Immediate Release: July 7, 1999)

Sahara's abrupt desertification started by changes in Earth's orbit, accelerated by atmospheric and vegetation feedbacks

WASHINGTON -- One of the most striking climate changes of the past 11,000 years caused the abrupt desertification of the Saharan and Arabia regions midway through that period. The resulting loss of the Sahara to agricultural pursuits may be an important reason that civilizations were founded along the valleys of the Nile, the Tigris, and the Euphrates. German scientists, employing a new climate system model, have concluded that this desertification was initiated by subtle changes in the Earth's orbit and strongly amplified by resulting atmospheric and vegetation feedbacks in the subtropics. The timing of this transition was, they report, mainly governed by a global interplay among atmosphere, ocean, sea ice, and vegetation. Their research is published in the July 15 issue of Geophysical Research Letters.

The researchers, headed by Martin Claussen of the Potsdam- Institut Fuer Klimafolgenforschung (Potsdam Institute for Climate Impact Research) employed a model of intermediate complexity to analyze climate feedbacks during the past several thousand years of the current, or Holocene, era. Called CLIMBER-2 (for CLIMate and BiosphERe, version 2.1), the model led to the conclusion that the desertification of North Africa began abruptly 5,440 years ago (+/- 30 years). Before that time, the Sahara was covered by annual grasses and low shrubs, as evidenced by fossilized pollen.

The transition to today's arid climate was not gradual, but occurred in two specific episodes. The first, which was less severe, occurred between 6,700 and 5,500 years ago. The second, which was brutal, lasted from 4,000 to 3,600 years ago. Summer temperatures increased sharply, and precipitation decreased, according to carbon-14 dating. This event devastated ancient civilizations and their socio-economic systems.

The change from the mid-Holocene climate to that of today was Initiated by changes in the Earth's orbit and the tilt of Earth's axis. Some 9,000 years ago, Earth's tilt was 24.14 degrees, as compared with the current 23.45 degrees, and perihelion, the point in the Earth's orbit that is closest to the Sun, occurred at the end of July, as compared with early January now. At that time, the Northern Hemisphere received more summer sunlight, which amplified the African and Indian summer monsoon.

The changes in Earth's orbit occurred gradually, however, whereas the evolution of North Africa's climate and vegetation were abrupt. Claussen and his colleagues believe that various feedback mechanisms within Earth's climate system amplified and modified the effects touched off by the orbital changes. By modeling the impact of climate, oceans, and vegetation both separately and in various combinations, the researchers concluded that oceans played only a minor role in the Sahara's desertification.

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Part II

On 12 July I wrote:

... I would like to know where all of the sand [in the Sahara] came from, too.

As if in answer to my rhetorical question, on the 16th I saw a featured article in New Scientist of 10 July titled "The riddle of the Sands". The subtext reads: "Deep in the Sahara lie vast deposits of incredibly pure glass. Nothing on Earth could have created them." It mentions the green glass forming the heart of a scarab found in Tutankhamen's tomb that is made of such glass. Walter Alter had written about this subject on 7 April and it was reprinted in Thoth III-8:

... An Italian geologist has taken a close look at the beautiful translucent scarab in a pectoral, or necklace, found by Howard Carter among the treasures of Tutankhamen. Carter thought the scarab was carved of greenish-yellow chalcedony. However, measuring its refraction revealed to Vincenzo De Michele that the gem consists of Libyan desert glass. This is a fused natural glass, formed by cooling molten sand. It results from the impact of a meteorite or comet or a low-altitude explosion in the atmosphere.

What makes the scarab even more astonishing is that the nearest source of Libyan desert glass is 500 miles west of the Nile, in the Western desert. Half of this distance lies beyond any known oasis. The glass is scattered over an area 15 miles in diameter. However, no meteor crater has been found, and the event responsible for the glass remains mysterious.

In March this year, I wrote: ... When I look at exposed strata on Earth, with the sharp physical and colour (often implying chemical) differences we see, I am more disposed to the extraterrestrial origin theory. That is particularly the case when a distinctive sequence appears globally. When we find stratification on the Moon and smaller, tectonically inert and unweathered objects we should be highly sceptical of geological models of their formation. ...

On 2 June this year, a NASA report said: ... Hammergren found that very elongated asteroids are never seen to be rotating faster than once every four hours. In contrast, more spherical asteroids can rotate as fast as once every 2.3 hours. Such evidence, Hammergren said, provides strong support for the theory that most asteroids are not tightly-bonded solid chunks of rock, but rather are loose aggregates of material, sometimes called "rubble piles."

On 24 June I replied to a query from Dick Gagel: ... In an Electric Universe scenario a comet will be destroyed before it hits the Earth by a discharge between the two. That is what I believe happened in Tunguska. That is not to say that the electric discharge itself would not be catastrophic - and we could cop a lot of glass fragments (tektites) and sand from the disrupted comet.

When the two June items are combined, and the distinction between comets and asteroids acknowledged to be purely one of ellipticity of orbits, then the probability of disruption by an electrical discharge becomes much greater. The melting of incoming material may then be explained by the action of an electric arc in space rather than ballistic heating in the Earth's atmosphere. The New Scientist report is very interesting in this regard:

"... The story that has begun to emerge since is both astonishing and mysterious. These glittering shards are the purest natural silica glass any one has ever found. And there may be more than 1400 tonnes of the stuff spread across a vast area of the desert. Some pieces contain tiny bubbles, wispy white deposits and swirling black patterns that hint at a tumultuous origin. Where on earth did this it [sic] from?

Tiny pieces of silica glass are fairly common in nature. When volcanic lava cools suddenly-as red-hot magma pours into the sea, for instance-molecules of silica in the lava freeze at random, creating an amorphous mass that resembles broken glass. But these materials are about 75 per cent amorphous silica at most. The rest is made up of crystals of quartz and oxides such as aluminium and iron. The desert glass is totally different: "It's the purest natural glass in the world," says Vincenzo de Michele, keeper of minerals at Milan's Museum of Natural History, "with a silica content of 98 per cent. This purity gives the desert glass some remarkable properties. ... you can heat the material to 1700 sC before it begins to melt - over 500 sC higher than other natural glasses. ... It can be dropped into cold water even when it is red hot and it doesn't disintegrate ...

Stroll across the desert site and you'll come across great big chunks of glass- some are larger than bowling balls and weigh as much as 26 kilograms. These massive pieces of [sic] dwarf lumps of natural glass found elsewhere. Also scattered about the site are clusters of sharp glass chips-the debris of prehistoric workshops-and ancient glass tools such as knives and hatchets, evidence of early interest in the silica glass. ... Geologists have dreamt up some pretty bizarre theories to explain the origins of this remarkable material."

One suggestion is that the glass may have formed at the bottom of a warm volcanic lake. But there were no hydroxide ions usually found in such glass and "geologists dated the glass at 28.5 million years old [while] the dried-up remains of the ancient lakes ... near the site turned out to be far too young-just 9000 years old." Another idea is that it may be volcanic but the whitish inclusions are minerals that form at much higher temperatures than are present in a volcano. And to cap it all, the dark samples are rich in iridium, typical of meteorites.

So the only explanation seems to be that the glass was formed upon impact of a meteorite into the desert. Certainly, some of the silica contains shocked quartz crystals which bolsters the impact theory but it does not explain the purity of the glass. Also, it must be remembered that impacts cause little melting and there is no impact crater in the vicinity. Any heating of the meteorite itself in the atmosphere causes mere superficial melting.

I believe the best explanation, given the purity of the glass, the size of some of the melts, and the presence of meteoritic elements - is heating in a plasma arc in space. Crystals embedded in a melt are a feature of chondritic meteorites and the shocked crystals would have retained the memory of their violent history - torn from the surface of a planet or moon by an interplanetary thunderbolt.

In this connection then it is noteworthy that the Apollo 15 astronauts found clear green glass at Hadley's rille on the Moon. And from Apollo 11; "All of the silicate minerals are unusually transparent and clear, because of the complete absence of hydrothermal alteration or weakening." Science Vol 167, No. 3918, 30 Jan 1970, p. 449. From the same issue (p.742) comes the estimate that each kg of moon dust contains no less than 40,000 glass spherules ranging in size from .03 mm to .75 mm. Many of the spherules have been impacted by tiny "micrometeorites". The report states "It is not known why the impacted particles resemble in color and appearance the kind of material from which so many spherules appear to have originated". But I detail on my CD the mechanisms that can create this effect in a plasma arc in space to produce chondritic meteorites.

The stratification found in the lunar soil indicates many episodes of deposition to form the regolith. The interplanetary discharge model has material electrically excavated from one body (the anode) and accelerated toward another body (the cathode) in the form of a self-contained plasmoid, rather like ball- lightning. The matter trapped therein will suffer extremely complex interactions. One effect is the melting, vapourization and ionization of matter nearest the axis of the arc. Electromagnetic sorting of ions by mass is then possible, yielding some regions of high purity. Other regions will not be heated to the same extent so that the final result may be a chaotic and violent mixing of solids, liquids and gases to form the matter that finally lands on the cathode or remains in space as meteors, asteroids and comets. Juergens went so far as to suggest that the lunar highlands were implanted in such a manner! I would merely say that it is not necessary to resort to problematic melting by impacts to produce the glass discovered on both the Moon and the Earth.

Of course, geological dating of the glass is meaningless if this scenario is correct. And the drying up of the lakes in the Sahara 9000 years ago may give some measure of how old the Saturnian stories may be.

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