What makes peat a nonrenewable energy source?

Peat is considered a nonrenewable energy source because it forms over thousands of years from the accumulation of partially decayed plant material in waterlogged conditions. The rate of peat formation is much slower than the rate at which it is being harvested for energy use, making it unsustainable in the long term. Once peat is extracted and burned, it cannot be easily replaced within a human lifetime.