Pracrise Listening 34 - Science & Technology Biogeochemistry - Thấm Tâm Vy

Nội dung text: Pracrise Listening 34 - Science & Technology Biogeochemistry - Thấm Tâm Vy

1. Science & technology How and why, roughly 2 million years ago, early human ancestors evolved large brains and Biogeochemistry began fashioning relatively advanced stone tools, is one of the great mysteries of evolution. Gold Leaf Some researchers argue these changes were brought about by the invention of cooking. They If you’re looking for gold, don’t look down. Look up. point out that our bite weakened around the same time as our larger brains evolved, and that it In the good old days, gold miners could seek out visible specks of bling at the surface in order takes less energy to extract nutrients from cooked food. As a result, once they had mastered the to find deeper, richer veins. These days, prospectors must examine samples of dirt for more art, early chefs could pare back their digestive systems and invest the resulting energy savings in minute traces suggestive of a hidden seam below. Analysing water from boreholes can also yield building larger brains capable of complex thought. There is, however, a problem with the clues, but boreholes are scarce and new ones are costly and time-consuming to drill. cooking hypothesis. Trees offer an alternative that is finally bearing fruit in Australia. The idea has been around Most archaeologists believe the evidence of controlled fire stretches back no more than 790,000 since the 1940s but, until now, never practical. Some trees have roots that reach deep years. Roger Summons of the Massachusetts Institute of Technology has a solution. Together underground, drawing up water and, along with it, tiny quantities of minerals that end up with his team of geomicrobiologists, he analysed 1.7m-year-old sandstones that formed in an distributed throughout the tree. In this way, even lofty leaves bear traces of what lies far beneath. ancient river at Olduvai Gorge in Tanzania. The region is famous for the large number of human The quantities are minuscule. In areas where there is no gold, leaves may have a background fossils that have been discovered there, alongside an impressive assembly of stone tools. The level of 0.15 parts per billion of gold; on gold-rich sites that can rise to 4 parts per billion. In sandstones themselves have previously yielded some of the world’s earliest sophisticated theory, “biogeochemical” prospecting is a simple matter of collecting leaves from across a site Acheulean hand axes: large tear-drop-shaped stone tools that are associated with Homo erectus. and mapping mineral concentrations to reveal subterranean treasures. It is best applied to dry Creating an Acheulean axe by repeatedly knocking flakes off of a raw stone in order to create regions where plants seek out water with deep roots. Some even break down soil to extract two sharp cutting edges requires a significant amount of planning. Their appearance is therefore mineral nutrients, thus increasing the amount of telltale minerals in their leaves. Gold is the thought to mark an important moment in cognitive evolution. Trapped inside the Olduvai obvious element to look for, but checking for elements that are associated with gold deposits, sandstones, the researchers found distinctive but unusual biological molecules that are often such as antimony and bismuth, can also be sensible. interpreted as biomarkers for heat-tolerant bacteria. Some of these thrive in water between 85 Sampling is harder than it sounds, though. Different trees accumulate gold in different ways, so and 95°C. The molecules’ presence suggests that an ancient river within the gorge was once fed exactly the same species must be sampled across each site for valid comparisons. Acacia is one by one or more hot springs, fitting nicely with its location within the geologically active East of the trees of choice, but Australia has about 1,000 Acacia species, many of which look similar. African Rift. The findings are published in a paper posted to the online bioRxiv preprint server. To confuse matters further, the degree to which elements accumulate in leaves varies with the Dr Summons and his colleagues say the hot springs would have provided a convenient “pre- seasons. fire” means of cooking food. In Rotorua in New Zealand, the Maori have traditionally cooked In proof-of-principle studies over the last few years, Nathan Reid and his team at CSIRO, food in geothermal springs (see picture), either by lowering it into the boiling water or by Australia’s national science agency, have shown that biogeochemical prospecting closely tallies digging a hole in the hot earth. Similar methods exist in Japan and Iceland, so it is plausible, if with the surface and groundwater analyses. Inspired by these results, Marmota, an exploration difficult to prove, that early humans might have used hot springs to simmer meat and roots. firm, put the method to the test at its Aurora Tank site, 50 km from the highly-productive Richard Wrangham, a primatologist at Harvard University who devised the cooking hypothesis, Challenger mine in South Australia. is intrigued by the idea. Nonetheless, fire would have offered a distinct advantage to humans, Leaves collected immediately around a known deposit that lies beneath ten metres of rock once they had mastered the art of controlling it since, unlike a hot spring, it is a portable contained traces of gold, validating the approach. Further samples were taken 40 metres apart resource. [The Economist UK, May 25, 2019] around known deposits, and at wider spaces farther out. This turned up several anomalies, where gold seemed to be present but other tests had shown nothing. “The usual calcrete [surface Notes sample] testing was saying ‘Don’t drill here’,” says Colin Rose, Marmota’s executive chairman, - bling: jewelry; gold “but the tree sampling was saying ‘Drill here’.” - seam: mép nối Then came the pay-off. Drilling revealed a five-metre-thick vein with 27g of gold per tonne, - tally: vật đối chiếu more than 30 metres below the surface. A metre-thick inner layer held an impressive 105g per - anomaly: độ chênh lệch bất thường tonne. Five grams per tonne is considered high-grade. Marmota is keen to explore further. In the - geomicrobiologist: nhà nghiên cứu outer sampling zone, the company found four anomalies in an area whereonly one potential seam địa vi sinh had been identified. They have yet to be drilled but plans are afoot. Prospecting with trees is - flake: mảnh sót lại starting to look less like a scientific curiosity and more like a golden opportunity. [The Economist UK, May 25, 2019] - gorge: hẽm núi - plausible (= reasonable): có vẻ hợp lý Human Evolution Stone-age Hot Pots Geothermal springs could help explain how human brains got so big Not a fire in sight Tha63m Ta6m Vy, May 31, 2019 PRACTISE LISTENING 34