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.
Here are some of the most common reasons that periods may be irregular: 1  Youâve just started menstruating. If you only recently got your period, it can take up to a year or more for your hormones to properly regulate. 2  If youâve been under a lot of stress. Stress can really effect hormones and female cycles. 3  If you have started birth control recently.