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Most water in Earth's atmosphere and crust comes from saline seawater, while fresh water accounts for nearly 1% of the total. The vast bulk of the water on Earth is saline or salt water, with an average salinity of 35‰ (or 3.5%, roughly equivalent to 34 grams of salts in 1 kg of seawater), though this varies slightly according to the amount of runoff received from surrounding land.
The deuterium to hydrogen ratio for ocean water on Earth is known very precisely to be (1.5576 ± 0.0005) × 10 −4. [36] This value represents a mixture of all of the sources that contributed to Earth's reservoirs, and is used to identify the source or sources of Earth's water.
Newborn. 0-3 months. 14-17 hours (including naps_ Infant. 4-12 months. 12-16 hours (including naps) Toddler. 1-2 years. 11-14 hours (including naps) Preschool
Can you really get by with just 6 hours of sleep a night? Here's what to know and how to get more sleep.
Is six hours of sleep enough? Doctors explain how much sleep you need, quality sleep basics, health effects of sleeping 6 hours and tips for better sleep.
The average sleep requirement is between seven and nine hours per day for an adult and nine to ten hours per day for a child; elderly people usually sleep for six to seven hours. Having less sleep than this is common among humans, even though sleep deprivation can have negative health effects. A sustained restriction of adult sleep to four ...
The American Sleep Foundation reports additional possible explanations, including menstruation, menopause, and pregnancy, all of which can interrupt sleep and lead to women staying in bed a little ...
It's suggested that idiopathic insomnia is a neurochemical problem in a part of the brain that controls the sleep-wake cycle, resulting in either under-active sleep signals or over-active wake signals. Sleep state misperception is diagnosed when people get enough sleep but inaccurately perceive that their sleep is insufficient. [128]