Here are notes on a few papers that caught my eye in recent editions of Science (3 April 2009), Nature (2 April 2009) and Nature Geoscience (April 2009).
A challenge to the consensus model of galaxy formation. Most conventional cosmologists think that galaxies formed in the early universe by the merging of smaller objects to form larger ones (what’s known as the ‘bottom up’ hypothesis). However, Collins et al. (2009) present observational evidence that the brightest galaxies at the centres of large clusters were almost as massive 9 billion years ago (conventionally speaking) as their counterparts today. They interpret this to mean that these galaxies had grown to more than 90% of their current mass within 4-5 billion years of the Big Bang, suggesting that the ‘bottom up’ theory, in which they must have undergone a longer period of hierarchical assembly, needs to be revised.
Mantle plumes have cooled down since the Mesozoic. Herzberg and Gazel (2009) describe petrological data showing that the amounts of MgO and FeO in Galápagos-related lavas and their primary magmas have decreased since the Cretaceous. These findings imply a cooling of the Galápagos mantle plume from about 1,560-1,620 oC in the Cretaceous to 1,500 oC today. A similar cooling trend is observed with the Iceland plume. Although there are exceptions, it seems that most pre-Cretaceous mantle plumes were hotter and melted more extensively than those beneath modern oceanic islands. This observation is very interesting in light of the proposal that the Flood/post-Flood boundary is located at or near the end of the Cretaceous. It looks as though we have evidence that the mantle plumes generated by catastrophic plate tectonics during the flood have been cooling down since that event.
Hotspot tracks reveal patterns of past mantle circulation. Also on the subject of mantle plumes, the bends observed in chains of volcanic islands and seamounts have often been attributed to changes in the motion of moving plates over stationary mantle hotspots. However, Tarduno et al. (2009) argue that several lines of evidence favour the hypothesis that such bends were caused by movements of the mantle plumes themselves. Changes in the flow of the mantle beneath the Pacific plate are said to have contributed to the development of the famous bend in the Hawaiian-Emperor chain, reminding us that the dynamics of the earth’s interior have played a formative role in geological history.
Evidence of oxygenated deep water ‘3.46 billion years ago’. Most conventional geologists accept that oxygenic photosynthesis had evolved by 2.7 billion years ago. However, the evidence for photosynthesis before that time is hotly disputed. Now Hoashi et al. (2009) have proposed that the haematite layers within the Marble Bar Chert of the Pilbara Craton in Western Australia provide evidence of the availability of free oxygen more than 700 million years earlier. The haematite crystals in these rocks are said to have precipitated when iron-rich hydrothermal fluids mixed with oxygenated sea water at depths >200 metres. Such a bold challenge to the conventional wisdom concerning the oxygenation of the atmosphere is bound to attract a great deal of comment and criticism in the months to come.
Collins C. A. and 17 others. 2009. Early assembly of the most massive galaxies. Nature 458:603-606.
Herzberg C. and Gazel E. 2009. Petrological evidence for secular cooling in mantle plumes. Nature 458:619-622.
Hoashi M. and 6 others. 2009. Primary haematite formation in an oxygenated sea 3.46 billion years ago. Nature Geoscience 2:301-306.
Tarduno J. and 3 others. 2009. The bent Hawaiian-Emperor hotspot track: inheriting the mantle wind. Science 324:50-53.