Conditions that promote karst development are well-jointed, dense limestone near the surface; a moderate to heavy rainfall; and good groundwater circulation. Limestone (calcium carbonate) dissolves relatively easily in slightly acidic water, which occurs widely in nature.
Crowther said first he had to figure out how many trees are on Earth and that number was far more than anyone expected: 3.04 trillion trees, according to a study published Wednesday in the journal Nature. 14 Photos Trees Around The World.
Nearly 4 billion trees worldwide are cut down each year for paper, representing about 35 percent of all harvested trees. This world map shows the Earth's vegetation.Source: NASA. Take a minute to look around the room youâre in and notice how many things are made out of paper.