Here's a breakdown:

1. Swampy Environments: Coal primarily forms in swampy environments, where large amounts of dead plants, like ferns, trees, and mosses, accumulate in waterlogged conditions.

2. Lack of Oxygen: The lack of oxygen in these swamps prevents the plant matter from fully decaying.

3. Burial and Pressure: Over time, layers of sediment (like mud, sand, or clay) bury the plant matter, increasing pressure and heat.

4. Transformation: The pressure and heat transform the partially decayed plant matter into peat, then lignite, then bituminous coal, and finally anthracite, the hardest and most carbon-rich type of coal.

Key Factors:

* Time: The process of coal formation takes millions of years.

* Plant Matter: The abundance of plant life in swampy environments is crucial.

* Pressure and Heat: These factors contribute to the transformation of plant matter into coal.

Let me know if you'd like more detail about any of these steps!