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.
Regular Periods. Before we can define an irregular period, we must first determine what a regular period is. People often say that a regular period occurs every 28 days, but actually, every woman's menstrual cycle is different. Depending on your body and your hormones, you may get your period every 20 days or your may get your period every 35 days.