是什么导致了早期美国例如电报、蒸汽船和织布机的重大发明的大量涌现？
What accounts for the great outburst of major inventions in early America—breakthroughs such as the telegraph, the steamboat and the weaving machine?
地球历史上的这次重大灾难以物种的大量消亡为标志；当时，地球上多达一半的物种都灭绝了。
This break in Earth's history is marked by a mass extinction, when as many as half the species on the planet became extinct.
该地区的农民们注意到了沼泽地生产力的重大下降，以及随之而来的干旱使得大量动物种群迁出。
Farmers in the area have seen a significant decline in the marsh's productivity as successive droughts have driven away many animal populations.
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