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Science Square (Issue 103)
Jan 1, 2015

Earth's most abundant mineral identified

Tschauner O. et al. Discovery of bridgmanite, the most abundant mineral in Earth, in a shocked meteorite. Science, November 2014.

A team of scientists has identified and characterized the Earth's most abundant mineral: "Bridgemanite" makes up about 70 percent of the Earth's lower mantle and 38 percent of its total volume. It is made of a high-density form of magnesium iron silicate and named after 1964 Nobel laureate physicist Percy Bridgman. For decades, scientists knew of the existence of dense Bridgemanite layers in the Earth's lower mantle (660 to 2890 km beneath the surface) through theoretical and some experimental studies. However, since the mysterious mineral never survived the trip to the surface, no one had been able to prove its existence. Conveniently, shock-compression that occurs in collisions of asteroids creates an identical hostile temperature (2100 C°) and high-pressure (240,000 times greater than sea-level) conditions to those found in deep layers of the Earth. As such, scientists decided to look at meteorites closely, particularly one that had fallen in Australia in 1879. By using a micro-focused X-ray beam in conjunction with electron microscopy, they were able to successfully detect the Bridgemanite grains for the first time. The discovery of the Bridgmanite's crystal chemistry will have a significant impact on the future studies of chemistry and geology of the Earth's deep mantle, and perhaps studies on the formation of the universe.

Male smokers lose Y chromosomes

Dumanski et al. Smoking is associated with mosaic loss of chromosome Y. Science, December 2014.

The Y chromosome is one of two sex-determining chromosomes in men, who have one X chromosome and one Y (women have no Y chromosomes, but two X chromosomes). During normal cell division, copies of all of the 23 chromosomes, including X and Y, are synthesized and sorted into the two new daughter cells. This complicated process sometimes goes wrong and chromosomes are lost. Cells with missing chromosomes usually die, but cells can still survive without a Y chromosome. Scientists initially thought that men lose Y chromosomes as they age and this is a part of the normal aging process. But later studies have shown that the age-dependent loss of Y chromosomes can have serious health implications, as it is linked to a shorter life span and an increased risk of dying from cancer. Even more troubling results came from a recent study that screened for associations between behavioral and lifestyle choices, and diseases. Comparison of the DNA in blood cells of over 6000 men suggested that blood cells from actively smoking men are 3-4 times more likely to be missing Y chromosomes than the nonsmokers in the control. These findings may explain why male smokers have a slightly increased risk of death from the majority of cancers than female smokers. The scientists hypothesized that the Y chromosome loss may create defective immune cells that cannot fight cancer and ultimately make the body susceptible to tumors. The study gives some good news to smokers though. Y chromosome damage by smoking is both reversible and dose-dependent, so you are always better off not smoking; it is never too late to quit.

The world's oldest case of cancer

Lieverse AR et al. Paleopathological Description and Diagnosis of Metastatic Carcinoma in an Early Bronze Age (4588+34 Cal. BP) Forager from the Cis-Baikal Region of Eastern Siberia. PLOS ONE, December 2014.

Cancer is responsible for one in four deaths in the Western world. It is widely assumed that cancer is a disease of modern times. Since people in older eras were exposed to fewer toxins, ate only natural foods, and adapted physically active lifestyles, many people thought that no one in older civilizations would have had cancer. Yet an analysis of a 4500-year-old skeleton from a cemetery in the Cis-Baikal region of Siberia has seriously challenged this idea. Researchers estimated that the Siberian man was about 35 to 45 years old before he died from a severe lung or prostate cancer. The ancient man's bones, from head to hip and including his upper arms and upper legs, were covered by lesions and big holes. It is almost certain that the deterioration of his bones left him immobile and eventually caused him a very agonizing death. It is also clear that those around him recognized his situation and placed him in a circular grave in the fetal position with some artifacts ,which is completely different from the rest of the burials in the cemetery. Although ancient skeletons with the scars of cancer are relatively rare, scientists suspect that cancer may have been considerably more common in ancient times than is generally predicted, especially when considering other variables such as naturally occurring carcinogens and longer life expectancies.