Author Topic: Tut's gem hints at space impact  (Read 2992 times)

Devious Viper
  • Guest
Tut's gem hints at space impact
« on: July 21, 2006, 01:55:25 PM »
In 1996 in the Egyptian Museum in Cairo, Italian mineralogist Vincenzo de Michele spotted an unusual yellow-green gem in the middle of one of Tutankhamun's necklaces.

The jewel was tested and found to be glass, but intriguingly it is older than the earliest Egyptian civilisation.

Working with Egyptian geologist Aly Barakat, they traced its origins to unexplained chunks of glass found scattered in the sand in a remote region of the Sahara Desert.

But the glass is itself a scientific enigma. How did it get to be there and who or what made it?

An Austrian astrochemist Christian Koeberl had established that the glass had been formed at a temperature so hot that there could be only one known cause: a meteorite impacting with Earth. And yet there were no signs of an impact crater, even in satellite images.

American geophysicist John Wasson is another scientist interested in the origins of the glass. He suggested a solution that came directly from the forests of Siberia.

"When the thought came to me that it required a hot sky, I thought immediately of the Tunguska event," he tells Horizon.

In 1908, a massive explosion flattened 80 million trees in Tunguska, Siberia.

Although there was no sign of a meteorite impact, scientists now think an extraterrestrial object of some kind must have exploded above Tunguska. Wasson wondered if a similar aerial burst could have produced enough heat to turn the ground to glass in the Egyptian desert.

The first atomic bomb detonation, at the Trinity site in New Mexico in 1945, created a thin layer of glass on the sand. But the area of glass in the Egyptian desert is vastly bigger.

Whatever happened in Egypt must have been much more powerful than an atomic bomb.

A natural airburst of that magnitude was unheard of until, in 1994, scientists watched as comet Shoemaker-Levy collided with Jupiter. It exploded in the Jovian atmosphere, and the Hubble telescope recorded the largest incandescent fireball ever witnessed rising over Jupiter's horizon.

Mark Boslough, who specialises in modelling large impacts on supercomputers, created a simulation of a similar impact on Earth.

The simulation revealed that an impactor could indeed generate a blistering atmospheric fireball, creating surface temperatures of 1,800C, and leaving behind a field of glass.

"What I want to emphasise is that it is hugely bigger in energy than the atomic tests," says Boslough. "Ten thousand times more powerful."

The more fragile the incoming object, the more likely these airborne explosions are to happen.

In Southeast Asia, John Wasson has unearthed the remains of an event 800,000 years ago that was even more powerful and damaging than the one in the Egyptian desert; one which produced multiple fireballs and left glass over three hundred thousand square miles, with no sign of a crater.

"Within this region, certainly all of the humans would have been killed. There would be no hope for anything to survive," he says.

According to Boslough and Wasson, events similar to Tunguska could happen as frequently as every 100 years, and the effect of even a small airburst would be comparable to many Hiroshima bombs.

Attempting to blow up an incoming asteroid, Hollywood style, could well make things worse by increasing the number of devastating airbursts.

"There are hundreds of times more of these smaller asteroids than there are the big ones the astronomers track," says Mark Boslough. "There will be another impact on the earth. It's just a matter of when."

Vivid777

  • High Priest
  • *****
  • Posts: 224
  • Karma: +0/-0
  • Things Are Not As They Seem
Re: Tut's gem hints at space impact
« Reply #1 on: November 25, 2008, 06:21:54 AM »

THE DOMINICK LABINO LECTURE
 

LIGHTNING MAKES GLASS

Vladimir A. Rakov

University of Florida, Gainesville

1. Introduction

Mother Nature makes glass each time a large amount of energy is released during a sufficient period of time at the Earth's surface, provided that the soil composition is suitable for making glass. The latter condition is satisfied, for example, by sandy soil, with the resultant natural glass being silica glass named "lechatelierite" after the French chemist Henry Le Châtelier (1850-1936). There are two phenomena that are responsible for making natural glass on Earth: meteorites and lightning. Glass that is made as a result of the collision of a meteorite with the Earth's surface is called meteoritic glass or tektite. Glass (a glassy object, to be exact) that is made as a result of a cloud-to-ground lightning discharge is called a fulgurite (from the Latin "fulgur" which means lightning). Fulgurites come in a great variety of forms and can be viewed as nature's own works of art. It is worth noting that lechatelierite (natural silica glass) is not present in obsidian, a glass-like material associated with volcanic activity. On the other hand, volcanic activity is known to generate lightning which, if it strikes sandy soil, may produce a fulgurite. Silica glass has been also made as a result of nuclear explosions. In 1945, the first nuclear bomb (equivalent to 18,000 tons of TNT) was detonated in the New Mexico desert. The explosion formed a crater 800 yards in diameter, glazed with a dull gray-green silica glass. This glass was named "trinitite" after Trinity Site where the first nuclear bomb test was conducted.

2. Characterization of Lightning

On average, about 100 lightning discharges occur every second on the Earth. Only about one-third of them involve ground (others occur in the cloud, between clouds, or between cloud and clear air) and potentially can make fulgurites. The Tampa area in Florida receives more than 12 lightning strikes per square kilometer per year. This is the highest level of lightning activity in the United States.

Each cloud-to-ground lightning involves an energy of roughly 109-1010 Joules. Most of the lightning energy is spent to produce thunder, hot air, light, and radio waves, so that only a small fraction of the total energy is available at the strike point. However, it is well known that this small fraction of the total lightning energy is sufficient to kill people and animals, start fires, and cause considerable mechanical damage to various structures. Lightning is also a major source of electrical disturbances.

The peak temperature of lightning channel is of the order of 30,000° K, which is five times higher than the surface temperature of the Sun (the temperature of the solar interior is 107 K). The lightning peak temperature is considerably higher than silica's melting point which is somewhere between 1600 and 2000° C depending on moisture content, but whether or not silica sand melts and glass is produced depends, besides other, not well-understood factors, on lightning duration. Some lightning strokes last (since a contact with ground is made) for less than a millisecond, others linger for a significant fraction of a second. Lightning current peaks are usually of the order of tens of kiloamperes, but occasionally may exceed 100 kA. The long-lasting current components are typically in the range of tens to hundreds of amperes. The latter are thought to be responsible for making fulgurites.

In the case of natural lightning, it is usually unknown when and where the discharge is going to occur. These uncertainties are largely removed when lightning is artificially initiated (triggered) from an overhead natural thundercloud with the so-called rocket-and-wire technique (for details visit our Web Site: http://www.eel.ufl.edu/~lightning). Some of the most interesting fulgurites have been created in triggered-lightning experiments.

About 30 to 40 lightning discharges are triggered every summer at the International Center for Lightning Research and Testing (ICLRT) at Camp Blanding, Florida. The Center is located approximately midway between Jacksonville and Gainesville, Florida, and is a unique facility for studying various aspects of atmospheric electricity, lightning, and lightning protection. The Center is operated by the University of Florida (UF). Examples of still photographs of lightning flashes triggered at Camp Blanding, Florida, are shown in Fig. 1. During summers of 1995 through 1998 over 30 scientists and engineers (excluding UF faculty, students, and staff) from 13 countries representing 4 continents performed experiments at the Center. Many triggered lightning discharges at the Center, that terminated on ground (as opposed to termination on well-grounded objects or systems) created fulgurites.

3. General Information on Fulgurites

The earliest discovery of a fulgurite was reportedly made in 1706 by Pastor David Hermann in Germany. Most people have never seen a fulgurite, and if they have they might not have recognized it for what it was. All fulgurites can be divided in two classes: sand fulgurites and rock fulgurites. Sand fulgurites are usually hollow, glass-lined tubes with sand adhering to the outside. Rock fulgurites are formed when lightning strikes the bare surface of rocks. This type of fulgurite appears as thin glassy crust with which may be associated short tubes or perforations lined with glass in the rock. Glass of this type may be relatively low in silica and exhibit a wide variety of colors, depending on the composition of the host rock. Rock fulgurites are found on the peaks of mountains.

When lightning strikes sandy soil, the air and moisture present in soil are rapidly heated, and the resultant explosion-like expansion forms the central tubular void. As stated before, quartz sand melts at a temperature of about 1600-2000° C depending on moisture content, and molten glass is pushed to the periphery of the void. Subsequent relatively rapid cooling causes the glass to solidify. A general condition for sand fulgurite formation appears to be the presence of a relatively dry dielectric such as quartz sand overlying a more conducting soil layer or the ground water table, with the depth of the latter probably determining the limit for vertical extent of the fulgurite formation. The diameter of fulgurites ranges from a quarter of an inch to 3 inches, and the color varies, depending upon the type of sand from which they were formed. Sand fulgurites are usually tan, grayish, or black, but almost translucent, white fulgurites have been found in Florida pan-handle beaches. The inner surface is glassy and exhibits numerous bubbles. The walls are usually about 0.5-2 mm thick, but may be paper thin. There appears to be no relation between tube diameter and wall thickness. Sand fulgurites are quite fragile and very difficult to excavate in one piece. An example of sand fulgurite is shown in Fig. 2.

Since fulgurites are real glasses, they are very resistant to weathering and are usually well preserved for a long period of time. For this reason they are used as paleoenvironmental indicators. For example, many fulgurites are found in the Sahara desert, where presently there is little lightning activity, confirming that very different conditions existed in this region in prehistoric times. A fossil fulgurite thought to be 250 million years old has been reported.

Fulgurites have been also produced artificially passing laboratory arc current through sand. It has been found by researchers at the Technical University of Ilmenau, Germany, that currents higher than 50 kA lasting for some hundreds of microseconds, typical of impulsive components of the lightning current are incapable of making a fulgurite (only some very thin fragments). On the other hand, relatively low magnitude currents of some hundreds of amperes lasting for some hundreds of milliseconds yielded well-formed fulgurites with diameters of 7 to 15 mm. It has been also observed that the higher the current the larger the cross-sectional dimensions of fulgurite. Different forms of fulgurites were obtained in dry and wet sand. Fulgurites in wet sand were more curved and had more irregular outer surface. The latter feature was attributed to the pressure of vaporized moisture that squashed the fulgurite when the arc pressure in the central tubular void disappeared, while the glass was still plastic.

4. Fulgurites Created at the ICLRT at Camp Blanding, Florida

4.1. Underground Power Cable Project (1993-1994)

In 1993, an experiment, sponsored by Electric Power Research Institute (EPRI), was conducted by Power Technologies, Inc. to study the effects of lightning on underground power cables. In this experiment three 15 kV coaxial cables with polyethylene insulation between the center conductor and the outer concentric shield (neutral) were buried 5 m apart at a depth of 1 m, and lightning current was injected into the ground at different positions with respect to these cables. One of the cables (Cable A) had an insulting jacket and was placed in PVC conduit, another one (Cable B) had an insulating jacket and was directly buried, and the third one (Cable C) had no jacket and was directly buried. About 20 lightning flashes were triggered directly above the cables which were unenergized.

The underground power cables were excavated by the University of Florida in 1994. The damage found ranged from minor punctures of the cable jacket to extensive puncturing of the jacket and melting of nearly all the concentric neutral strands near the lightning attachment point. Some damage to the cable insulation was also observed. In the case of the PVC conduit cable installation, the side wall of the conduit was melted, distorted and blown open, and the lightning channel had attached to the cable inside and damaged its insulation. Photographs of the damaged parts of the cables are shown in Fig. 3.

Five fulgurites were found during the excavation of the underground cables. The excavation process was a slow, methodical one and covered an area with dimensions of 4 m x 20 m. Various techniques developed in paleontology were used to remove the fulgurites. The fulgurite excavated over Cable B was nearly vertical with a length approximately 1 m and an average diameter of 1.5 cm at the top and about 0.4 cm at the cable. This fulgurite was the most complete fulgurite excavated as part of the underground power cable project. It was unearthed in one piece with very little reconstruction necessary. This fulgurite is presently on exhibit at the Electric Power Research Institute (EPRI) in Palo Alto, California.

4.2. World-Record Fulgurite (1996)

After the excavation of fulgurites produced as part of the underground power cable project we started checking for fulgurites at all known lightning strike points at the Camp Blanding facility. Each year we trigger on average 30 to 40 discharges some of which strike ground as opposed to terminating on the rocket launcher. Additionally, the facility receives about 5 lightning strikes that occur naturally, irrespective of our lightning triggering activity. Our surveillance cameras and observer reports allow us in many cases to find the strike point on the ground. Such strike points usually appear as holes in the ground with the surrounding grass being killed (as becomes apparent within a few days). When the strike point on the ground is found and flagged, it is impossible to predict if a fulgurite has been created, and, if so, what its shape and dimensions are. One such find in 1996 led to many days of careful digging and resulted in the unearthing of a fulgurite having two mostly vertical branches, one about 16 feet and the other about 17 feet long. It was recognized by the Guinness Book of Records as the world's longest excavated fulgurite. The 17-foot branch of the world-record fulgurite is shown in Fig. 4. The successful excavation would not be possible without special tools and the paleontological skills of Mr. Dan Cordier and Mr. Mike Stapleton. The world-record fulgurite was carefully separated into sections and covered in plastic material used in paleontological digs. Each section was measured with special instruments and labeled for subsequent reassembling. At this time, the world's longest fulgurite is looking for a home - a museum with sufficient space to display this magnificent subterranean creation of atmospheric electricity. We have dug up about ten other fulgurites at Camp Blanding that are on average 4-5 feet long.