August, 2006

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Fossil Embryos of Complex Animals Revealed to be Older

Major gap in the record of metazoan evolution exists between Cambrian and Precambrian because the Precambrian metazoans were too small and soft to leave fossilized remains. A research team led by Chen Junyuan of the Nanjing Institute of Geology and Palaeontology, CAS, has recently revealed the discovery of fossil embryos that resemble those of modern bilaterally symmetrical animals such as molluscs and annelids. Their work was published in the recent issue of Science ( Science 312, 1644-1646).

They have isolated several dozen thousands of embryos in the last few years through acetic acid solution from the phosphate rocks. These rocks come from Wengan, Guizhou, deposited at least 580 million years ago and they predate by 40 million years the start of the Cambrian time, when metazoans diversity exploded.

Through electronic scanning microscope observation, they surprisingly discovered 248 embryos that had presence of an acellular protrusion (called polar lobe) from one of the cleavage cell in each embryo. These 580 million embryos consist of trilobed, J-shaped and five-lobed structures that are the early cleavage morphologies unique to modern lobe-forming embryos in bilaterally symmetrical animals such as molluscs and annelids. Through the protrusion and absorption of the polar lobe from embryos, these animals ensure segregation of maternal cytoplasmic substances (including a number of critical important morphogenesis factors) to certain cell (or cells), but not others.

This research team includes members from different institutions in China (including Taiwan), USA and French, specialized in diversified research fields. This team successfully proved that the presence of predicated neck-like structure of polar lobe by using the state-of-the-art synchrotron radiation microtomography. Xian Dingchang, o ne of the research members from the Institute of High Energy Physics (CAS Member, CAS), says that it is the first time to use this technology for a non-destructive study of fossil internal structure and the result shows its great potential for fossil study.

The study of Chen's team proves the result not only reveal that complex animal life including bilaterally symmetrical animals had a very ancient history, but also implies that polar lobe delivering certain molecules to one of the cells in the early embryos is a very ancient process of the symmetry-break mechanism.-12

¡°Thermal Depression¡± Considered to be a Key Factor Causing Dust Storms

A research team headed by Research Fellow Kuang Yaoqiu from the Guangzhou Institute of Geochemistry, CAS, considered that there are misunderstandings about the source areas of dust storms among domestic researchers, based on their studies on key areas of source of dust storms in the world. They suggested that deserts might not be the source areas of dust storms and the monsoon might not definitely cause dust storm. According to the monitoring results from satellites, the ground temperatures of the source areas of dust storms are obviously lower than that of the neighboring areas, which causes a ¡°depression¡± with noticeably lower temperature. Such ¡°thermal depression¡± is one of the key factors that lead to the instability of the atmospheric system. It is the underlying surface with temperature markedly lower than that of its neighboring area that makes the air currents go downwards and raises the sand and dust from the ground. Hence the sand and dust storms are formed.-13

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