Geoscientist Online

Phoenix rising

The lander at the Martian North Pole, Phoenix, has dug a shallow trench in the soil. It had difficulty in delivering the sample to a small oven on board, because the soil clumped and failed to sift through a screen. Amazingly, the team on Earth were able to convey a message to shake the soil more, and this was successful. The ovens are designed to reach a temperature of 1800 degrees: different elements burn off at different temperatures. The first test reached 95 degrees, the second 350 degrees. Had there been any ice, it would have melted: they detected no water at all, but plenty of carbon dioxide, of which the Martian atmosphere is primarily composed.

The Martian atmosphere also contains more dust than that of the Earth. The sample can be studied by microscopy, electrochemistry and a conductivity analyser. The sample contains almost 1000 separate particles, some smaller than one tenth of the diameter of human hair. There are shiny black specks and smaller reddish particles. So far four minerals have been identified. The robotic arm has only dug down five to eight centimetres so far and white material is visible, showing through the brown soil. It could be ice or salt. The lack of water detected suggests that it may not be ice. It could be carbon dioxide ice (‘dry ice’) – though the team believe that they may be on the edge of a polygon (a small mound bounded by a shallow trench, a familiar terrestrial landform in permafrost regions). Tests of the minerals will show whether any water is bound up in them.

The $420 million dollar Phoenix mission is aimed at finding out whether Mars is, or ever was, suitable for rudimentary life forms to exist there. 

JMcC

Hickman Crater?

Dr Arthur Hickman (Western Australian Geological Survey) has discovered a crater while engaged in research on channel ore deposits¹. This is a ‘rim crater’, one that has not eroded significantly from its original shape, and is only exceeded in size by the well-reserve Wolf(e) Creek Crater². The rim of the new find stands 80m above the floor, and mainly exposes rhyolite. The crater is 260m in diameter and its depth, allowing for infill is about 50m. The age is estimated as between 10,000 to 100,000 years. It sits on the top of a plateau about 36km from the iron-ore mining town of Newman, and it only visible from the air.

Alex Bevan of the Western Australian Museum has not seen it, but considers that it could only be a meteorite crater. The most likely impactor is an iron meteorite, though a stony meteorite is not impossible³. An impactor diameter of c. 10m is likely, travelling at a speed of 5 km/sec on impact - exploding with energy release equivalent to 200,000-300,000 tons of TNT. It is possible that diligent search will reveal unaltered iron meteorite fragments nearby, as such fragments have been found close to the Barringer Crater, Arizona and the Wolfe Creek Crater, having separated from the falling mass before impact. 

JMcC

Refs

1. http://www.dailygalaxy.com/my_weblog/2008/04/major-impact-cr.html
2. McCall, G.J.H. 1965. Possible meteorite craters: Wolf Creek and analogues. Annals of the New York Academy of Science 123 (Art2), 970-998.
3. McCall, G.J.H. 2008. Carancas fall. Geoscientist 18(6); 5.
   
   
   

Amphibious pachyderms

A team, including Alexander Liu from Oxford and Dr Eric Seiffert from Stony Brook, New York, has studied the fossil teeth of two species that belong to an extinct family of mammals from the late Eocene, 37 million years ago^1,2. The isotopic signals from oxygen and carbon atoms in these specimens suggest that both Barytherium and Moertherium were largely aquatic, living in swamps and rivers, and feeding on freshwater vegetation. They were probably not fully aquatic, the researchers say, for they lacked a streamlined body or flipper-like limbs. Their mode of life was similar to that of present-day hippos.

These beasts probably resembled present-day tapirs - hoofed animals that look like a cross between a horse and a rhino. They may have been forced out onto land during an end-Eocene cooling event; though evidence to support this suggestion is at present lacking. The fossils were unearthed in the deserts of Egypt, where, at that time, the land was covered by tropical rain forests and swamps. DNA evidence supports this conclusion, elephants being related to the seagoing manatees and dugongs. It also suggests that elephants are related to hyraxes – the ‘conies’ of biblical literature. 

JMcC

Refs

1. Liu, A. et al. Proceedings of the National Academy of Sciences, April 15, 2008.
2. http://news.bbc.co.uk/2/hi/science/nature/7347284.stm  
   
   
   

Gooseberries go it alone

The "molecular clock" method based on genes has for some years been used to establish phylogenomic relationships, despite problems and misgivings from time to time^1,2. The raison d’être for using the technique is stated as: “the unlikelihood of fossilisation of the earliest representative taxa, for which the record is perhaps unreliable…” 1. However, a new study reports a massive analysis of 39.9Mb of expressed sequence tags from 29 animals belonging to 21 phyla - including 11 previously lacking genomic data. The report makes difficult reading for the layman (just what is ‘bootstrap support’, exactly?) but several important new conclusions are clear.  The most surprising of these is that comb-jellyfish (Ctenophora, which include the Sea Gooseberries - picture) separated first from the Metazoan mainstream to create their own evolutionary path.

Ctenophora have both radial and bilateral symmetry, are bell-shaped, with the mouth situated at the broader end: they have eight meridians and move by strokes of iridescent paddles. They are quite distinct from Scyphomedusae, Trachylina and Siphonophora. Hitherto, it had been supposed that those relatively amorphous creatures the sponges were first to separate. The reader is left with a sense of amazement at the complicated paths of development of animals on this planet, all through the happenstance workings of mutation and natural selection.  

JMcC 

Refs 

1. Donoghue,P.J.C , Smith, M.P. (Eds.) 2004. Telling the Evolutionary Time: Molecular Clocks and the Fossil Record. CRC Press, Boca Raton; 288 pp.
2. Graur, D., Martin, W. 2004. Reading the entrails of chickems; molecular timescales of evolution and the illusion of precision. Trends in Genetics 20(2); 80-86.
3. Dunn, C.W., Hejnol, A., Matus, D.Q. et al. 2008. Broad phylogenomic sampling improves resolution of the animal tree of life. Nature 452 (10); 745-749.