Which sentence incorrectly describes the formation of petroleum? About 300 million years ago, the seas and oceans were inhabited by tiny plants and other organisms. These organisms died and were buried on the ocean floor. Over time, their bodies were covered with silt and mud that was rich in organic material, forming layers of organic matter. This matter was subjected to high temperature and pressure. In such conditions, oxygen was available in abundance. Over a period of many years, the matter decomposed and formed oil and gas.