Coal is formed from ancient dead plants that were buried in swamps, then slowly “cooked” by heat and pressure inside Earth over millions of years, turning first into peat and then into different ranks of coal like lignite, bituminous, and anthracite. This very slow process is called coalification or carbonation, which is why coal is considered a non‑renewable fossil fuel.

Quick Scoop

From swamp plants to peat

Long ago (often in the Carboniferous Period, about 300 million years ago), dense forests and swamp plants died and fell into waterlogged, low‑oxygen bogs where they could not fully rot. Layer upon layer of this dead vegetation built up, was partly decomposed, and compacted into a soggy, carbon‑rich material called peat, which is the first step toward coal.

Peat buried and “cooked”

Over time, sediments like sand and mud buried the peat deeper underground, increasing temperature and pressure. As the peat was squeezed and heated, it lost water and gases such as carbon dioxide and methane, concentrating the carbon and slowly transforming it into coal; this long transformation is known as coalification or carbonation.

Stages and types of coal

Coal passes through several stages, each with more carbon and energy content and less moisture. The main stages are:

  • Peat → not yet coal, partially decayed plant material.
  • Lignite → “brown coal,” soft, low carbon, relatively low energy.
  • Bituminous coal → “soft coal,” higher carbon and widely used for power and industry.
  • Anthracite → “hard coal,” very high carbon, shiny, and the highest energy content among the coal ranks.

Why it takes so long

Coal formation requires:

  1. Huge amounts of plant growth in swampy, low‑oxygen environments.
  2. Burial by sediments during changing sea levels and tectonic movements.
  3. Millions of years of sustained heat and pressure at depth.

Because all these steps take geological timescales, the coal we burn today records ancient environments and cannot be replaced on human timescales, so it is classed as a non‑renewable fossil fuel.

Today’s context and impact

Modern coal use mainly involves burning bituminous and sub‑bituminous coals for electricity and industry, taking advantage of their high combustibility. However, burning coal releases large amounts of carbon dioxide and other pollutants, making it a major driver of climate change and air‑quality problems and a focus of current energy and environmental policy debates.

Information gathered from public forums or data available on the internet and portrayed here.