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.
There is an unequal distribution of land and water between the two hemispheres. The Southern Hemisphere has less land and more water. The Northern hemisphere is about 60.7% water and 39.3% land. The Southern hemisphere is about 80.9% water and 19.1% land. 63.7% of Earth's land mass is above the Equator.