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Humans have so profoundly altered the Earth that, some scientists argue, our current geologic epoch requires a new name: the Anthropocene. But defining the precise start of the era is tricky. Would it begin with the spread of domesticated farm animals or the appearance of radioactive elements from nuclear bomb tests? Scientists report in ACS' Environmental Science & Technology a method to measure levels of human-made contaminants in sediments that could help pinpoint the Anthropocene's onset.
The geologic record can sometimes provide clear-cut evidence of epoch changes. For example, when a meteorite collided with Earth 66 million years ago, levels of the metal iridium from the space rock spiked in sediments around the world. This clearly marked the end of the Cretaceous period. However, trying to define the start of the proposed—and much debated—Anthropocene could be more complicated. Human influence over the climate and environment began with the Industrial Revolution in the 1800s, and accelerated dramatically in the second half of the 20th century. Many markers of human impact on the planet from agriculture, waste disposal and other activities have been archived in the planet's sedimentary records. The rise in industrial chemicals, such as pesticides and pharmaceuticals, is another example of a human-driven activity that has been captured in...
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