How and when was oil formed? (Site 1)

70% of oil deposits existing today were formed in the Mesozoic age (252 to 66 million years ago), 20% were formed in the Cenozoic age (65 million years ago), and only 10% were formed in the Paleozoic age (541 to 252 million years ago).

Oil is a fossil fuel that has been formed from a large amount tiny plants and animals such as algae and zooplankton. These organisms fall to the bottom of the sea once they die and over time, get trapped under multiple layers of sand and mud. The more heat, the lighter the oil.