Limestone turns into the metamorphic rock marble when it is subjected to high amounts of pressure and heat. Marble is a metamorphic rock formed by the alteration of limestone by heat and pressure. The calcite in the limestone changes and fossils and layering in the original limestone disappear as interlocking grains grow. If the limestone is pure, a white marble is formed. The population of the world is never stable; the number of births and deaths affect its change. With better health facilities due to development in medical science, now the number of deaths is lower than before. Birth rate is a statistic that measures the number of live births per 1000 people.