Nonrenewable describes natural resources that cannot be replaced once we use them up, at least not within a human lifespan or even thousands of years.

Coal, oil, and natural gas are nonrenewable resources. These fossil fuels formed over millions of years from ancient plants and animals buried deep underground. Once we burn them for energy, they're gone. We can't make more coal the way we can plant more trees or wait for the sun to rise again tomorrow.

The opposite of nonrenewable is renewable. Solar energy is renewable because the sun keeps shining. Wind power is renewable because wind keeps blowing. Trees are renewable because we can plant new ones. But the oil we pump from the ground took millions of years to form, so when it's gone, it's gone.

Many minerals and metals are also nonrenewable, though we can sometimes recycle them. The copper in pennies or the iron in steel came from ore that took millions of years to form in the Earth.

Understanding which resources are nonrenewable helps us make smart decisions about how we use them. It's like having a special collection that you can never replace: you might use pieces of it, but you'd think carefully about when and why, knowing that once it's gone, you can't get more.