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 your periods have suddenly become exceptionally irregular, then it could also mean that you have a cyst that can burst. Yes every woman will know that the periods are never ever very regular, but in case of an ovarian cyst that can burst, they will become extremely erratic - much more than normal.