Nearly everything you own was either grown or mined. The phone in your pocket holds dozens of elements dug from the ground on several continents; the building you sit in is made largely of sand, gravel, limestone and iron. Earth science explains where these materials come from, why they are found where they are, and why some will be harder to get in future.

Renewable and nonrenewable

Some resources, such as sunlight, wind and river water, are renewed constantly. Others are not. Resources that form far more slowly than we use them, such as oil, coal and metal ores, are treated as nonrenewable. Oil is still forming today, but over millions of years, so on a human time scale the supply is fixed. Groundwater can fall on either side: a shallow aquifer refilled by rain each year is renewable, while ancient groundwater in a dry region is effectively being mined.

What makes an ore

Almost every rock contains a little copper, gold or iron, but usually far too little to bother with. An ore is rock in which a useful mineral is concentrated enough to be mined at a profit. That definition is partly economic: when prices rise or methods improve, rock that was waste becomes ore. Nature concentrates metals in several ways. Hot, mineral-rich fluids moving through cracks deposit veins of copper, lead, zinc or gold. Some minerals settle out of cooling magma. And placer deposits form when rivers sort sediment and gather heavy grains, such as gold, in their gravels, which is why the 1848 California gold rush began with flakes glinting in a stream. Most of the world's iron comes from vast banded layers laid down on ancient sea floors when the oceans first filled with oxygen.

Fossil fuels

Fossil fuels store energy captured by living things long ago. Coal formed from plants buried in ancient swamps, while most oil and natural gas formed from tiny sea organisms, such as plankton, buried in mud on the sea floor. Contrary to a popular image, dinosaurs contributed almost nothing. Burial must be just right: too shallow and the material never cooks into oil; too deep and hot, and it breaks down into gas. Oil and gas then seep upward until they are trapped beneath a layer of rock they cannot pass, where drillers find them. Burning these fuels also releases the carbon dioxide that is warming the climate.

Reserves and resources

Estimates of how much is left use two different terms. Reserves are deposits that are known and can be extracted profitably with today's methods; the larger total resource also includes deposits not yet found or not yet worth extracting. Reserves therefore change as prices and technology change. In 1956 the American geologist M. King Hubbert forecast that oil production in the lower forty-eight United States would peak around 1970. He was right: output peaked and fell for decades. But new methods, horizontal drilling and hydraulic fracturing, made oil in shale rock worth extracting, and US output passed its old peak in 2018. The lesson is that forecasts of running out rest on assumptions about price and technology, as well as geology.

The same logic applies to the minerals in electronics and clean energy. Rare earth elements are not especially rare in the crust; what is scarce is rich deposits that are easy to mine and separate. Their supply chains are concentrated in a few countries, which turns geology into geopolitics.

The hidden costs

The resource we use most after water is perhaps the least glamorous. Sand and gravel are the most extracted solid materials on Earth, mainly for concrete and roads. Desert sand is little use, since wind rounds its grains too smoothly to bind well, so builders dig riverbeds and beaches, sometimes causing erosion and flooding downstream. Mining can poison water when exposed rock reacts with air and rain to form acid. And the burdens of extraction often fall on people with little power: some cobalt in the Democratic Republic of the Congo, which supplies most of the world's cobalt, is dug by hand in dangerous small mines, at times by children. Recycling, more efficient use and better rules for mining are all ways to meet human needs without treating miners or their neighbors as mere means.

Worked example: a battery's journey

Follow the materials in an electric car battery. Its lithium may come from Australian hard rock or from salty brine pumped beneath the high salt flats of Chile, Argentina and Bolivia and evaporated in huge ponds, in a desert where local communities worry about water. Its cobalt may come from the Congo, its nickel from Indonesia, its graphite from China, its copper wiring from Chile or Peru. When lithium prices soared in 2021 and 2022, companies reopened and developed deposits that had not been worth mining, so reserves grew: the concept from this level in action. As batteries wear out, they become a new kind of ore, and recycling plants are being built to recover their metals, turning yesterday's products into tomorrow's raw materials.