Previous studies have already pinned some pretty global effects on humans. There is, for instance, the fact that humans are now the largest earth-moving force on the planet. There are the rising sea levels linked to global warming and the wave of extinctions being seen around the world. There is even a carbon isotope difference in today's sediments, caused by humans burning fossil fuels. All will leave lasting marks on the geologic record. Some researchers argue that the change came when coal arrived on the scene, around 1800, followed by steam engines that dramatically increased the power of humans to reshape the surface of the Earth. It's the difference between a plow pulled by a horse and a bulldozer, Zalasiewicz told Discovery News. "Humans can basically do a whole lot more," said Zalasiewicz. There were also a lot more humans around -- about a billion by 1800, he said. "If this suggestion is going to be taken seriously by mainstream geologists, then we have to discuss when the (human-caused) changes became dominant," said Zalasiewicz. Some researchers are in favor of establishing the Anthropocene, but consider the geologists' criteria too conservative. "They are Earth scientists trying to look at it a traditional way," said civil and environmental engineer Braden Allenby of Arizona State University. In other words, geologists are trying to anticipate how the present epoch will appear in the geological record to geologists tens of thousands of years from now. But it's clear today that there are big changes underway all over the planet. "In terms of biology," said Allenby, "there's probably not a place on Earth that's not affected by humans." Which raises another question: Are we truly in a new epoch, or just serving the same role as an asteroid impact, i.e., ending one epoch and making room for the next? Two centuries may be a lot in terms of human history, but it's insignificant in terms of geological time. "We don't know just yet," Allenby told Discovery News. "We're just beginning the story here. It may be that we're just a flash in the pan."
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