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 cool would that be to stand amongst the company of fellow laureates like Mother Teresa or Albert Einstein? We have some ideas for scoring you one (nominating yourself isn't one of them).
He's ventured to the abyss of black holes, wagered on the information paradox and floated around in zero gravity. Meet the man, the legend, the super scientist: Stephen Hawking.