Lead 210 dating
The simplest form of isotopic age computation involves substituting three measurements into an equation of four variables, and solving for the fourth.
In many cases, there are independent cues (such as geologic setting or the chemistry of the specimen) which can suggest that such assumptions are entirely reasonable.Over time the uranium-238 very slowly decays into uranium-234 (half-life = 248,000 ).Radium-226 in the soil exhibits the same level of radioactivity as uranium-238 from which it was originally derived, because of a natural phenomenon called secular equilibrium.From the accumulation rate, the age of sediment from a particular depth in the sediment column can be estimated.) and for these purposes can be considered to be present at an unchanging concentration (over time) in the earth's crust.Although the concentration of uranium varies from location to location, it is present in essentially all soils and sediments, at least at some low level.Since the 1960s, however, there has been a growing concern about the health effects of lead.
For instance, scientists have found that lead can cause mental and physical problems in growing children.
However, the methods must be used with care -- and one should be cautious about investing much confidence in the resulting age...
especially in absence of cross-checks by different methods, or if presented without sufficient information to judge the context in which it was obtained.
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One of the oldest examples of lead is a small statue found in Egypt.