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.
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.n 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.