Fifty percent of the total mass of the atmosphere is located in the lower 5.6 km (18,000 ft) of the troposphere. It is primarily composed of nitrogen (78%) and oxygen (21%) with only small concentrations of other trace gases.
Having irregular periods is very common. I see them in my practice all the time. The causes can range from something insignificant to something that requires treatment. For example, if you're a teen, your body's hormones can fluctuate and take some time until they find a balance.
While 3-5 days is most common, anywhere between 2 and 7 days is considered normal. See your doctor if your period lasts longer than a week or suddenly changes from what's regular for you.1  Previous. 2  Continue.or most women, periods usually occur from 21 to 35 days apart. In young girls and teenagers, periods are commonly irregular and have cycles ranging between 21 and 45 days. Keep track of your periods on a calendar (which can help you and your doctor determine what pattern is normal for you). 1  Previous. 2  Continue.