June 6, 2012. Earth may be nearing an ecological tipping point that threatens biodiversity, food production and water supplies as humans consume resources at an unsustainable pace. About 43 percent of the Earth's surface has been built upon or is being used for agriculture to support the planet's 7 billion inhabitants, according to Anthony Barnosky, a professor of integrated biology at the University of California, Berkeley. As that figure approaches 50 percent, there may be irreversible and significant environmental changes. Humans consume 2.25 acres of resources per capita, and with the Earth's population projected to reach 9 billion by 2045, half of all land may be in use by 2025, Barnosky said. That includes Antarctica, Greenland and other mostly uninhabitable regions. Small-scale ecosystems have shown that once 50 percent of an area is altered, biodiversity is often lost and animal and plant species are at risk of extinction, he said.