6. the average copper ore mined in 1900 was five percent copper by weight. copper ore mined in 1990 was approximately 0.5 percent copper by weight. what factors could account for this difference? "

The volume of miners and industries using copper in the 20th century presented an exponential growth. Mining tends to extract the highest grade resources first, once they are the most profitable. With the intense activity achieved during the last century, the higher grade non renewable sources were quickly depleted, forcing the industry to start exploring lower grades sources to satisfy the demand.

It is also noteworthy that mining copper of higher quality causes more damage to the environment, having its protocols and restrictions consequently addressed by the legislation. Therefore the costs of mining 5% copper might be outweighed by a higher margin of profit from 0.5% copper which also is less damaging to the environment.

d.he wanted to send diplomats to communist countries.

jim crow law, in u.s. history, any of the laws in which racial was enforced, in the south between the finish of reconstruction in 1877 and the start of the social liberties development during the 1950s.

jim crow was the name of a minstrel routine( jump jim crow) performed starting in 1828 by its creator, thomas dartmouth ("daddy") rice, and by numerous imitators, including on-screen character joseph jefferson.

the term came to be a defamatory sobriquet for african americans and an assignment for their segregated life. the segregation rule was stretched out to parks, graveyards, theaters, and eateries with an end goal to keep any contact among blacks and whites as equivalents.

it was classified on neighborhood and state levels and most broadly with the "separate yet equivalent" choice of the u.s. preeminent court in plessy v. ferguson (1896).