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.
Your period is irregular if. 1  it comes more frequently than 21 days. 2  you go 35 days or more between periods. 3  the length of your cycles varies greatly (even if they are typically within the 21 to 35-day range)