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.
But, anywhere from 2 to 7 days is normal. For the first few years after menstruation begins, longer cycles are common. A woman's cycle tends to shorten and become more regular with age. Most of the time, periods will be in the range of 21 to 35 days apart. Your period suddenly stops for more than 90 days. 2  Your periods become very irregular after having had regular, monthly cycles. 3  Your period occurs more often than every 21 days or less often than every 35 days. 4  You are bleeding for more than 7 days.