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.
Over seven million species of plants and animals live on planet earth, according to the best estimates made by biologists. If you add in the world's species that aren't plants or animals, such as lichens, mushrooms and bacteria, the total number of species leaps much higher. Tallying the estimates of all living things brings the number to 11.3 million species currently on earth.