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.
If you are experiencing other symptoms alongside irregular periods, such as abdominal pain, it is important to see a doctor to rule out other conditions. Irregular periods can be a sign of a variety of other conditions, such as polycystic ovary syndrome (POCS) or uterine cancer.