Posted by: paulgarner | April 9, 2009

Science, Nature and Nature Geoscience: a miscellany

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.

References

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.

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Responses

  1. The K-T boundary is the boundary between Flood and post-Flood deposits? The thickness of Cenozoic sediments is greater than 25,000 feet (7600 m) along the Gulf of Mexico coast in Louisiana and Texas. To say that all of this was deposited after the Flood is extremely unrealistic.

    • Several lines of evidence suggest that the Flood/post-Flood boundary is at or near the Cretaceous/Palaeogene boundary. Perhaps most importantly, this is where thick, uniform and transcontinental sedimentary packages give way to regional- to local-scale ones, and where palaeocurrents change from consistent continent-wide patterns to scattered basin-controlled patterns. Furthermore, above this boundary we find evidence of mammalian stratomorphic series (e.g. the famous horse series) in which the morphological changes appear to track a change in climate from wetter to drier and from warmer to cooler, consistent with an earth recovering from the global flood. The dramatic tectonic and climatic changes that North America would have experienced at this time, with such phenomena as superquakes, supervolcanoes and hypercanes, are likely to explain the rapid accumulation of sediments along the Gulf coast and elsewhere. The post-Flood world was undoubtedly a wild kind of place and I may post more on this in the near future.

  2. I’m only sort-of clear on the terms here: K-T = Cretaceous/Palaeogene = Flood? (roughly?)

    Then the Cenozoic layer comes on top, right? This would all be stuff laid down after the Flood was done?

    So a 4.7 miles thick layer of dirt are laid down after the Flood is done?? Am I missing something? That’s a whole mountain range of stuff being laid down across an area. I could see that being done by a global flood, but after the floodwaters have already receded? Am I understanding that correctly?

    • Many creationists (me included) regard the Palaeozoic and Mesozoic sediments as having been deposited during the Flood. The Cretaceous/Palaeogene boundary (i.e. the top of the Mesozoic) thus represents the transition from Flood to post-Flood geological activity. This placement of the boundary is supported by the various lines of evidence outlined above in my response to Kevin.

      Yes, this means that we have to explain substantial thicknesses of post-Flood sediments in some localities, although, as pointed out above, the Cenozoic sequences are generally much smaller in scale than the transcontinental packages characterising the Flood deposits. We need to remember that the early post-Flood period was very active geologically. Not only was there residual catastrophism from the Flood, but also dramatic isostatic readjustments and associated superquakes, the melting of plates that had been rapidly subducted during the Flood (leading to the development of volcanic chains like the Cascades) and lots of precipitation – factors that would have resulted in high rates of erosion and sedimentation.


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