Planetary science: Tunguska at 100
The most dramatic cosmic impact in recent history has gathered up almost as many weird explanations as it knocked down trees, writes Duncan Steel.
Possible Existence of Anti-Matter in Bulk
OF the many craters on the Earth known to have been produced by fallen meteors, a few have left no signs of the meteor which caused them, apart from the huge holes created in the Earth's crust. Large meteorite fragments have been found in or near most craters. A possible explanation of the lack of meteorite fragments in the other cases is that the meteors concerned were of contraterrene constituency (anti-matter). In this case no traces of the meteors would remain, due to the annihilation process. One of these events, from which no fragments appear to have survived, has occurred in recent years. In 1908 a meteor1, apparently of great size, was seen passing over western Russia; a few minutes later it crashed in the Siberian wastes with an explosion, effects of which were felt for hundreds of miles around, and seismographs thousands of miles away registered its impact. Descriptions of its effects at the time indicated a release of power equivalent to that which might have been obtained from a thermonuclear explosion. No expedition to the site of its landing was undertaken until 1927, when the devastation found even at 40 miles from the site was almost inconceivable; but no fragments of the meteor were located despite the several huge though shallow craters which it had caused. If this meteor consisted of anti-matter an obvious explanation is at hand for the devastation found, the lack of meteoric material, and the great size reported in eye-witness accounts of its passage.
Live birth in the Devonian period
The extinct placoderm fishes were the dominant group of vertebrates throughout the Middle Palaeozoic era, yet controversy about their relationships within the gnathostomes (jawed vertebrates) is partly due to different interpretations of their reproductive biology. Here we document the oldest record of a live-bearing vertebrate in a new ptyctodontid placoderm, Materpiscis attenboroughi gen. et sp. nov., from the Late Devonian Gogo Formation of Australia (approximately 380 million years ago). The new specimen, remarkably preserved in three dimensions, contains a single, intra-uterine embryo connected by a permineralized umbilical cord. An amorphous crystalline mass near the umbilical cord possibly represents the recrystallized yolk sac. Another ptyctodont from the Gogo Formation, Austroptyctodus gardineri, also shows three small embryos inside it in the same position. Ptyctodontids have already provided the oldest definite evidence for vertebrate copulation, and the new specimens confirm that some placoderms had a remarkably advanced reproductive biology, comparable to that of some modern sharks and rays. The new discovery points to internal fertilization and viviparity in vertebrates as originating earliest within placoderms.