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 may be heavy the first day or so each time and then decrease on later days. Periods usually last between three and five days. It is normal to have periods that are shorter or longer, up to seven days. It is also normal if your periods are not the same number of days each month, especially in the first years.eep in mind that your periods may not be regular at first. You may have two in one month, or have a month without a period at all. Periods will become more regular in time. To learn about your own pattern, itâs a good idea to keep track of your periods on a calendar.