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.
World Population 2017. The current US Census Bureau world population estimate in 2016 shows that there are approximately 7,346,235,000 people on earth as of August 23, 2016, which far exceeds the population of 7.2 billion from 2015.