Outline the method for dating rocks and fossils using radioisotopes
sapiens: .1 million years – large brain, flat face, reduced teeth, reduced robustness, chin D.5.4 State that adaptations (or micro-evolutionary steps) may occur as the result of an allele frequency increasing in a population over a period of time. p squared = frequency of homozygous dominants p squared = (.463)(.463) = .214 2pq = frequency of heterozygotes 2pq = 2 (.463)(.537) = .497 If there is random mating in a population, the chance of inheriting two copies of the first of the two alleles is (p)(p). erectus: .4 - 1.8 million years – more complex tools so meat significant part of diet and changed teeth. neanderthensis .5 million years – larger brains and bones, larger teeth and jaw, shorter limbs for the cold H. If q = frequency of t allele, q squared = .288 so q = .537 If p = frequency of T allele, p = (1 - q) = .463 The frequency of homozygous dominants (TT) and heterozygotes (Tt) can be calculated.Typically commonly occurring fossils that had a widespread geographic distribution such as brachiopods, trilobites, and ammonites work best as index fossils.If the fossil you are trying to date occurs alongside one of these index fossils, then the fossil you are dating must fall into the age range of the index fossil. In a hypothetical example, a rock formation contains fossils of a type of brachiopod known to occur between 410 and 420 million years. africanus: 2.3 - 3 million years – flatter face, larger molars for plant based diet A. afarensis: 3 - 3.9 million years – ape-like face A. habilis: 1.6 - 2.4 million years – smaller teeth and jaw for meatier diet, first with tools, size like humans H. robustus: 1.4 - 2.2 million years – very large molars, bones and skull H.
The atoms in some chemical elements have different forms, called isotopes. There are two main methods determining a fossils age, relative dating and absolute dating.Relative dating is used to determine a fossils approximate age by comparing it to similar rocks and fossils of known ages.The same rock formation also contains a type of trilobite that was known to live 415 to 425 million years ago.Since the rock formation contains both types of fossils the ago of the rock formation must be in the overlapping date range of 415 to 420 million years.
Carbon-14, the radioactive isotope of carbon used in carbon dating has a half-life of 5730 years, so it decays too fast.