Humans have altered Earth so much that scientists say a new epoch in the planet's geologic history has begun.

Say goodbye to the 10,000-year-old Holocene Epoch and hello to the Anthropocene.

Among the major changes heralding this two-century-old man-made epoch:

The idea, first suggested in 2000 by Nobel Prize-winning chemist Paul Crutzen, has gained steam with two new scientific papers that call for official recognition of the shift.

Vivid metaphor

In the February issue of the journal GSA Today, a publication of the Geological Society of America, Jan Zalasiewicz and Mark Williams of the University of Leicester and colleagues at the Geological Society of London argue that industrialization has wrought changes that usher in a new epoch.

Scientists of the future will have no trouble deciding if the proposal was timely. All they'll need to do is dig into the planet and examine its stratigraphic layers, which reveal a chronology of the changing conditions that existed as each layer is created. Layers can reflect volcanic upheaval, ice ages or mass extinctions.

"Sufficient evidence has emerged of stratigraphically significant change (both elapsed and imminent) for recognition of the Anthropocene �?currently a vivid yet informal metaphor of global environmental change �?as a new geological epoch to be considered for formalization by international discussion," Zalasiewicz's team writes.

The paper calls on the International Commission on Stratigraphy to officially mark the shift.

In a separate paper last month in the journal Soil Science, researchers focused on soil infertility alone as a reason to dub this the Anthropocene Age. (The term "age" is sometimes used interchangeably with "epoch" or to indicate a transition period between epochs.)

As an example, they said, agriculture in Africa "has so degraded regional soil fertility that the economic development of whole nations will be diminished without drastic improvements of soil management."

"With more than half of all soils on Earth now being cultivated for food crops, grazed, or periodically logged for wood, how to sustain Earth’s soils is becoming a major scientific and policy issue," said Duke University soil scientist Daniel Richter.

Richter's work was supported by the National Science Foundation, the U.S. Department of Agriculture, the Andrew W. Mellon Foundation.

Origin of a term

Earth's 4.5-billion-year history is divided into major eras, then periods and finally epochs. The Holocene Epoch began after the last Ice Age.

As early as the late 1800s scientists were writing about man's wholesale impact on the planet and the possibility of an "anthropozoic era" having begun, according to Crutzen, who is credited with coining the term Anthropocene (anthropo = human; cene = new) back in 2000. That year, Crutzen and a colleague wrote in the scientific newsletter International Geosphere-Biosphere Programme about some of the dramatic changes:

"Urbanization has ... increased tenfold in the past century. In a few generations mankind is exhausting the fossil fuels that were generated over several hundred million years."

Up to half of Earth's land has been transformed by human activity, wrote Crutzen and Eugene F. Stoermer of the University of Michigan. They also noted the dramatic increase in greenhouse gases and other chemicals and pollutants humans have introduced into global ecosystems.

The epochal idea has merit, according to geologist Richard Alley of Pennsylvania State University.

"In land, water, air, ice, and ecosystems, the human impact is clear, large, and growing,"Alley told ScienceNow, an online publication of the American Association for the Advancement of Science. "A geologist from the far distant future almost surely would draw a new line, and begin using a new name, where and when our impacts show up."