Final answer:
Petroleum forms through the decomposition and transformation of organic material over millions of years. Oil and natural gas are the result of this process, with their formation depending on various factors such as the type of organic matter and burial conditions.
Step-by-step explanation:
Petroleum forms through the breakdown of vast quantities of microscopic plants and animals in the oceans. Over hundreds of millions of years, these organic remains are compressed and transformed under layers of silt or shale rock, resulting in the formation of oil and natural gas. The specific type of fossil fuel formed depends on factors such as the type of organic matter, the burial conditions, and the temperature and pressure levels.
The process begins with the burial of organic material under ocean or river sediments. Heat, pressure, and bacteria then combine to decompose and transform the organic material. In most areas, oil forms first, while in deeper, hotter regions underground, natural gas is formed.