Context: The great majority of asphalt used commercially is obtained from petroleum. Nonetheless, large amounts of asphalt occur in concentrated form in nature. Naturally occurring deposits of asphalt/bitumen are formed from the remains of ancient, microscopic algae (diatoms) and other once-living things. These remains were deposited in the mud on the bottom of the ocean or lake where the organisms lived. Under the heat (above 50 °C) and pressure of burial deep in the earth, the remains were transformed into materials such as asphalt/bitumen, kerogen, or petroleum.

Question: From where does most asphalt come?
Answer: petroleum

Question: What are the sources of natural deposits of asphalt?
Answer: once-living things

Question: How much heat is required for the natural production of asphalt?
Answer: above 50 °C

Question: Besides heat, what other requirement is needed to form asphalt?
Answer: pressure

Question: What other product of heat and pressure does the formation of asphalt and petroleum  produce?
Answer: kerogen

Question: Most of the petroleum used for commercial purposes is obtained from what?
Answer: Unanswerable

Question: Current living things are the source of what?
Answer: Unanswerable

Question: What product of heat and pressure does the formation of asphalt and microscopic algae produce?
Answer: Unanswerable

Question: Besides pressure, what is required to form mud?
Answer: Unanswerable

Question: Besides heat, what is required to form Besides pressure, what is required to form mud??
Answer: Unanswerable