From LiveScience:
Humanity's Longest-Lasting Legacy: Miles of Holes
It's estimated that humans have altered over half of the planet's surface, and those changes are easy to see – the ice sheets are melting, forests are shrinking and species are going extinct.*A Day in the Life, Beatles, 1967.
People have changed the planet so dramatically that some geologists think the Earth has entered a new phase in its geological timeline, named the "Anthropocene." But what about the marks humans are leaving deep underground?
"Because it's not in our immediate living environment, it doesn't seem as significant," said Jan Zalasiewicz, a senior lecturer in palaeobiology at the University of Leicester, in the United Kingdom. But, as Zalasiewicz and two of his colleagues argue in a new study, human activity below the surface is permanently changing Earth, and a sprawling web of holes from mining and energy exploration provides more evidence the planet has entered the Anthropocene. [World's Weirdest Geological Formations]
Out of sight, out of mind
The distance to the center of the Earth is roughly 3,960 miles (6,373 kilometers). Animal life stops 1.2 miles (2 km) below the surface — the depth where miners discovered deep-dwelling worms in South African gold mines. All known microbial life stops at a depth of around 1.7 miles (2.7 km). But humans have left a permanent mark well beyond those depths, geologists say.
When an animal dies, it only leaves behind one skeletal record of itself, but the same animal might leave hundreds of so-called trace fossils in the form of burrows. Most animals leave behind trace fossils a few inches deep. The deepest burrowers are Nile crocodiles, which dig dens up to 39 feet (12 meters) deep. The deepest-reaching plant roots belong to the Shepherd's tree in Africa's Kalahari Desert, which can reach 223 feet (68 m) deep. Humans also leave trace fossils behind, but these typically reach as deep as 7.6 miles (12.3 km) and are permanently changing rock layers....MORE
There are about 1 million boreholes in the United Kingdom,
according to the National Geoscience Data Centre.
Credit: British Geological Survey © NERC 2014
Credit: British Geological Survey © NERC 2014
