What are Braxton Hicks contractions? Braxton Hicks contractions can begin as early as the second trimester. However, they are most commonly experienced in the third trimester. When this happens, the muscles of the uterus tighten for approximately 30 to 60 seconds, and sometimes as long as two minutes.
Main articles: Hydrology and Water distribution on Earth. Water covers 71% of the Earth's surface; the oceans contain 96.5% of the Earth's water. The Antarctic ice sheet, which contains 61% of all fresh water on Earth, is visible at the bottom. Condensed atmospheric water can be seen as clouds, contributing to the Earth's albedo.
* Meteoric water-is water in circulation * Connate water - fossil water, often saline. * Juvenile water-water that comes from the interior of the earth. * Surface water-water in rivers, lakes, oceans and so on. * Subsurface water-Groundwater, connate water, soil, capillary water * Groundwater-exists in the zone of saturation, and may be fresh or saline. The movement of water is referred to as the global water cycle (hydrologic cycle). Precipitation, evaporation/transpiration, and runoff (surface runoff and subsurface infiltration) are the primary phases in the hydrologic cycle. The global water budget is based on the recycling (movement, storage, and transfer) of the Earths water supply.