Answer:
Carboniferous
Step-by-step explanation:
The Carboniferous was a geological period in which the Earth was much warmer, with the climate being warm and wet in most of it. During this period, the land was covered with dense rain forests. These rainforests were dominated by gymnosperms. Gymnosperms are the plants that have seeds that are not enclosed in an ovary, but instead they are ''naked seeds''. These plants, or rather trees were the ones that actually gave the material for the formation of the large coal deposits.