地球开启新纪元“人类世”?

Since the middle of the 20th century, humans have had a very strong effect on planet Earth. These effects have included climate change, species loss and pollution. Humanity's impact has been so strong that scientists say a new geological epoch began then.

The scientists call it the Anthropocene epoch. The word comes from the Greek terms for "human" and "new." This epoch started sometime between 1950 and 1954, the scientists say.

There is evidence worldwide of the harmful impact on the Earth's health of burning fossil fuels, dropping nuclear weapons and releasing fertilizers and plastics on land and in water.

"It's quite clear that the scale of change has intensified unbelievably and that has to be human impact," said University of Leicester geologist Colin Waters. He led the Anthropocene Working Group.

The scientists say the power of humans is comparable with the meteorite that crashed into Earth 66 million years ago. The meteorite killed off the dinosaurs and started the Cenozoic Era, or what is known as the age of mammals. While that meteorite started a whole new era, the working group is proposing that humans only started a new epoch. An epoch is a much smaller geological time period.

The scientists are proposing a small but deep lake outside of Toronto, Canada, to place a historic marker. The lake is called Crawford Lake. The group aims to decide on an exact start date of the Anthropocene by measuring plutonium levels at the bottom of Crawford Lake.

Crawford Lake is 29 meters deep and 24,000 square meters wide. It was chosen over 11 other sites because the yearly effects of human activity on the earth's soil, atmosphere and biology are clearly shown in its layers of sediment. That includes everything from the effect of nuclear weapons to pollution to rising temperatures.

There are clear signs in Crawford Lake showing that, starting in 1950, "the effects of humans overwhelm the Earth system," said Francine McCarthy. She is part of the working group who specializes in that site as an Earth sciences professor at Brock University in Canada.

The Anthropocene shows the power — and hubris — of humankind, several scientists said. Hubris is a great or foolish amount of confidence.

"The hubris is in imagining that we are in control," said former U.S. White House science adviser John Holdren. He was not part of the working group of scientists. He disagrees with the group's proposed start date. Instead, he wants one much earlier. Holdren said the power of humans to change the environment is far greater than their understanding of the impacts.

Geologists measure time in eons, eras, periods, epochs and ages, with eons being the longest. The scientific working group is proposing that Anthropocene Epoch followed the Holocene Epoch. Holocene started about 11,700 years ago at the end of an ice age.

The proposal still needs to be approved by three different groups of geologists. It could be signed at a major conference next year.

Naomi Oreskes is a science historian with Harvard University and a working group member. She said if there is no change to harmful human activities, "we are headed for tragedy."

I'm Dan Novak.

Dan Novak adapted this story for VOA Learning English based on reporting from Associated Press.

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species — n. a group of animals or plants that are similar and can produce young animals or plants

impact — n. a powerful or major influence or effect

geology — n. a science that studies rocks, layers of soil, etc., in order to learn about the history of the Earth and its life

epoch — n. a period of time that is very important in history

fertilizer — n. a substance that is added to soil to help the growth of plants

scale — n. : a device that is used for weighing people or things

meteorite — n. a piece of rock or metal that has fallen to the ground from outer space

sediment — n. material that sinks to the bottom of a liquid

overwhelm — v. to cause to have too many things to deal with

hubris — n. a great or foolish amount of pride or confidence