After the second half-life has elapsed, yet another 50% of the remaining parent isotope will decay into daughter isotopes, and so on.
For all practical purposes, the original isotope is considered extinct after 6 half-life intervals. A small portion of a meteorite is vaporized in the device forming ions.
The early sculptures known as the Venuses of Tan-Tan and Berekhat Ram, are such crude representations of humanoid shapes that some experts doubt whether they are works of art at all.
Also used to describe the process of genetic change within a population, as influenced by natural selection.
adaptive landscape: A graph of the average fitness of a population in relation to the frequencies of genotypes in it.
Peaks on the landscape correspond to genotypic frequencies at which the average fitness is high, valleys to genotypic frequencies at which the average fitness is low. adaptive logic: A behavior has adaptive logic if it tends to increase the number of offspring that an individual contributes to the next and following generations.
If such a behavior is even partly genetically determined, it will tend to become widespread in the population.
Trees undergo spurts in growth in the spring and summer months while becoming somewhat dormant in the fall and winter months.
When a tree is cut down, these periods are exhibited in a cross section of the trunk in the form of rings.Characteristics The earliest forms of prehistoric art are extremely primitive.The cupule, for instance - a mysterious type of Paleolithic cultural marking - amounts to no more than a hemispherical or cup-like scouring of the rock surface.Despite seeming like a relatively stable place, the Earth's surface has changed dramatically over the past 4.6 billion years.Mountains have been built and eroded, continents and oceans have moved great distances, and the Earth has fluctuated from being extremely cold and almost completely covered with ice to being very warm and ice-free.Meteorites are among the oldest objects we know about - formed about 4.5 billion years ago. This article describes the principles and methods used to make that determination.