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.
Irregular Periods Perimenopause. Irregular periods in perimenopause are common and completely normal due to your ovaries producing less progesterone and estrogen. Due to the decline of these hormones you may also begin to experience hot flushes and night sweats, loss of libido, vaginal dryness and mood swings.