2 Measuring vitamin D levels is also expensive, costing between $50 and $220 per test in commercial laboratories for patients without insurance. Another challenge is that the level of 25-hydroxy-vitamin D that should be considered normal is unclear.
The closer a planet is to the sun, the shorter the time to complete one revolution is. Mercury, for example, has an orbital period of 88 days while it takes Jupiter about 11.86 years. The period of the Earth's orbit is usually thought to be 365 days as calendars show. However when averaged it is actually about 365.25 days, which requires an extra day on the calendar every four years (causing a leap year). Contradictions within orbit times are probably caused by the ages of the sources.
Best Answer: A period or age is a time span of many millions of years that are assumed to have had similar characteristics. On the geologic time scale, a period is longer than an epoch and shorter than an era. Since, Earth is about 4.6 billion years old. Earth scientists divide its age into shorter blocks of time. The largest of these are eons, of which there are three in Earthâs history.