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.
For a detailed explanation of where Earth's water is, look at the data table below. Notice how of the world's total water supply of about 332.5 million mi3 of water, over 96 percent is saline. Of total freshwater, over 68 percent is locked up in ice and glaciers. Another 30 percent of freshwater is in the ground.