keannu
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Source : 12 graders' mockup test, April, 2022, No 39
Ore deposits represent work that nature does for us. For instance, Earth’s crust contains an average of about 55 ppm (parts per million) of copper, whereas copper ore deposits must contain about 5,000 ppm (0.5%) copper before we can mine them. Thus, geologic processes need to concentrate the average copper content of the crust by about 100 times to make a copper ore deposit that we can use. We then use industrial processes to convert copper ore into pure copper metal, an increase of about 200 times. By a fortunate coincidence, elements and materials that we use in large amounts need less natural concentration than those that we use in small amounts. Thus, we are likely to have larger deposits of mineral commodities that we use in large amounts. As long as energy costs remain high, the relation between work that we can afford to do and work that we expect nature to do will control the lower limit of natural concentrations that we can exploit, and this puts very real limits on our global mineral resources.
I don't understand the two bold sentences. What do they mean? This is a scientific writing, hard to understand.
Ore deposits represent work that nature does for us. For instance, Earth’s crust contains an average of about 55 ppm (parts per million) of copper, whereas copper ore deposits must contain about 5,000 ppm (0.5%) copper before we can mine them. Thus, geologic processes need to concentrate the average copper content of the crust by about 100 times to make a copper ore deposit that we can use. We then use industrial processes to convert copper ore into pure copper metal, an increase of about 200 times. By a fortunate coincidence, elements and materials that we use in large amounts need less natural concentration than those that we use in small amounts. Thus, we are likely to have larger deposits of mineral commodities that we use in large amounts. As long as energy costs remain high, the relation between work that we can afford to do and work that we expect nature to do will control the lower limit of natural concentrations that we can exploit, and this puts very real limits on our global mineral resources.
I don't understand the two bold sentences. What do they mean? This is a scientific writing, hard to understand.
