Marl, a natural mixture of clay and calcium carbonate. It is a loose, earthy substance, usually gray or bluish in color. Marl deposits are formed in shallow lakes. The calcium carbonate marl is derived from the biological action of certain aquatic plants on dissolved carbonates. Shell marl contains shellfish remains. Greensand marl contains glauconite, or greensand, a silicate of potassium and iron. Marl is used to neutralize acid soils. Portland cement is sometimes made with marl instead of limestone.
How do scientists find details about the early days of our solar system? One way is to investigate comets. Find out how the Deep Impact spacecraft fired an impactor into Comet Tempel 1 to get some answers.
While routinely scanning the stars, NASA scientists came across something they didn't expect to see: a vast area of space empty of stars, planets and matter.