Australasian Tektites Research Articles

Tektites and Geomagnetic Reversals

THE microscopic glassy objects which occur in sediments deposited in the Australasian area during and shortly after the last magnetic polarity reversal are apparently tektites (see succeeding communication). The last reversal occurred 0.7 × 106 yr ago: potassium–argon dates1 indicate that the Australasian tektites were formed 0.7 × 106 yr ago. The tektites were formed and deposited at the same time as the geomagnetic field reversed, and so both phenomena could have a common cause.

Critique of ‘Cometary impact and the origin of tektites’

Lin [1966] recently outlined two mechanisms by which he suggests that it is dynamically possible for the Australasian tektites to have originated from an impact on earth by some gigantic cosmic body. He calculates that the energy of such an event, in order to remove the earth's atmosphere, would excavate a crater over 300 km in diameter. It is the purpose of this critique to indicate, quite apart from pointing out that 300-km craters associated with the possibility of terrestrial tektite origin are undiscovered, that both mechanisms suggested by Lin are contradicted by present aerodynamic and petrographic data on Australasian tektites. Also, we emphasize here a conclusion inherent in Lin's analysis, but not explicitly stated by him: namely, that, in comparison to the magnitude of atmosphere-removing events, such relatively insignificant earth cavities as the Ries and Bosumtwi craters (thought by some, from age considerations, to be sources of tektites) are far too small to be associated energetically with atmosphere removal.

Tektites and Geomagnetic Reversals

THE microscopic glassy objects which occur in sediments deposited in the Australasian area during and shortly after the last magnetic polarity reversal are apparently tektites (see succeeding communication). The last reversal occurred 0.7 × 106 yr ago: potassium–argon dates1 indicate that the Australasian tektites were formed 0.7 × 106 yr ago. The tektites were formed and deposited at the same time as the geomagnetic field reversed, and so both phenomena could have a common cause.

Cometary impact and the origin of tektites

The possibility of a terrestrial origin of tektites is re-examined in the light of recent aerodynamic evidence presented by Chapman, Larson, and Anderson. It is found that even though existing evidence points strongly toward a lunar origin as most probable for Australasian tektites, there still exists the possibility that these small glassy objects originated on the earth. In particular, it is conceivable that a sufficiently energetic cometary collision of the type hypothesized earlier by Urey could momentarily blow a bubble through the earth's atmosphere and hence propel small objects over intercontinental distances. The minimum mass of a comet head required to accomplish such a feat is estimated to be about 5×1017 grams. Some obvious questions which remain to be answered in order to support such a model of tektite origin are discussed.

Some alkali and titania analyses of tektites before and after G-1 precision monitoring

A comparison of 55 older analyses of Australasian tektites with 110 modern precisely monitored analyses suggests that more than half of the older alkali and titania determinations are decidedly inaccurate and misleading. Deviations of the older analyses from the restricted values of the modern analyses are comparable to the imprecisions shown by early analyses of G-1 granite and W-1 diabase. This suggests that a high percentage of older alkali and titania analyses, such as those of Washington's tables, are of questionable quality.

On the unity and origin of the Australasian tektites

Aerodynamic experiments with tektite glass demonstrate that, subsequent to the termination of ablation, high thermal stresses are formed within a thin outer shell. This shell spontaneously spalls, leaving a core shaped like many of the tektites found in Billiton, Java, Philippines and Australia. Certain tektite fragments from Java and Australia are shown to have the same internal stress patterns as pieces of aerothermal stress shell. The over-all evidence indicates that the Australasian tektites descended into the atmosphere as rigid objects of glass. Core shapes found in the extreme southwest part of Australia surprisingly are more like those found in the Philippines than in other areas of Australia; comparisons of chemical analyses and of specific gravity population polygons reveal the same striking circumstances. It is concluded that all Australasian tektites represent a single event. A study of tektite forms, in relation to results from laboratory experiments, indicates that the temperature of formation of primary shapes varied progressively across the Australasian strewnfield. The sculpture on certain australites provides a record of tumbling during entry into the Earth's atmosphere. The effect of turning on the determination of entry trajectories is discussed, and new evidence is presented pertaining to the deceleration which existed when ablation terminated on the australites. The trajectory determinations correspond to an origin from the Moon. Numerous trajectories from the Moon to Earth have been studied with a high-speed electronic digital computer. The relative probability of such trajectories is about 1 200 for the Moon as a whole, and 1 60 for certain crater locations. A comparison of the geographical spread of the Australasian tektites with the Earth landing patterns for lunar material ejected within the a zimuthal dispersion observed of lunar rays, and within the elevational dispersion measured in hypervelocity impact experiments, indicates mutual compatibility.

Population polygons of tektite specific gravity for various localities in Australasia

Measurements of specific gravity by the method of liquid flotation have been made on about 6000 tektites from 18 different localities in Australasia, from 1 locality in Texas and 2 in Czechoslovakia. Comparison of specific-gravity population polygons for various localities has led to the unanticipated conclusion that the australite population in southwest Australia is essentially the same as the philippinite population, rather than the population elsewhere in Australia. The javanite population appears closely related to certain populations in Australia. In several localities the presence of two superimposed populations is demonstrated. The specific-gravity evidence indicates that the Australasian tektites represent a single event comprising many distinguishable clusters, some of which have partially overlapped.