News from Nature & More
Another article has been published relating to some of the predictions made in my New Year's prediction list (although to be fair, this paper was pre-published online in December), Nature (today's edition-subscription required) has a discussion on the fossils found in the Doushantuo fossil beds (China). The original findings indicated that the fossils included embryonic forms of metazoans. What the study indicated was that, at 599 million years old, these fossils were some of the oldest evidence of complex life. What's more, these fossils preceded the so-called "Cambrian Explosion" (~523 million years ago) by nearly 80 million years. These findings would suggest that the Cambrian 'explosion' was something more like a slow burn. So that's where the science stood until today.
Authors Bailey et al. argue that many of the putative 'eggs' and 'embryos' are in fact sulphur-reducing bacteria and thus far simpler forms that metazoan life. The study was based on structural and size similarities to modern-day sulphur-reducing bacteria. Thus, according to these findings, the metazoan origin of some of the fossils at Doushantuo should be questioned. In fact, one of the original problems with these finds is how exactly eggs and embryos were preserved, but not the metazoans that produced them.
A word of warning. The 'hype' on this find is sure to focus on the fact that some of the 'eggs' and 'embryos' have been misindentified and that the deeper origins of the Cambrian explosion should be dropped. However, the authors make no such assertion. In fact, in their concluding statement they make it very clear that this is not their argument:
We do not suggest that the Doushantuo microbiota is composed entirely of sulphur bacterial remains, because there are many structures in the Doushantuo that clearly do not resemble sulphur bacteria.
As usual, science examines every find with a careful and critical eye. This study will no doubt cause the original investigators (along with others) to re-evaluate the fossil finds at Doushantuo.
On another note, a very interesting article is to appear in the journal Earth and Planetary Science Letters that is sure to create a few fireworks. Ophiolites are rocks that are thought to represent ancient seafloor that is obducted (thrust onto) continental crust during the process of collision. This process is relatively common in modern-style plate tectonic regimes. There is some debate about whether or not modern-style plate tectonics existed in the Archean (pre 2500 million years ago). The earth was hotter then and presumably oceanic crust was able to remain afloat and not sink as it does today when it ages. Thus, one of the major debates in Earth science is when modern style tectonics started.
In 2004, Tim Kusky and co-authors published an article in Science on the 'world's oldest ophiolite' from China. The rocks nearby the ophiolite (but not the actual ophiolite itself) dated to 2,500 million years old and Kusky and co-authors argued that modern style plate tectonics occurred by the end of the Archean. The previous record for oldest ophiolite was about 500 million years younger than this. The paper caused a stir, but subsequent papers questioned the interpretation of the rocks offered by Kusky along with the age. The paper in EPSL again mentions possible problems with the study and reports a new age on the 'ophiolitic rocks' of only 297 million years! These sorts of controversies usually result in some fireworks amongst the competing scientists!