2 methods dating fossils
Carbon-14, or radiocarbon, is a naturally occurring radioactive isotope that forms when cosmic rays in the upper atmosphere strike nitrogen molecules, which then oxidize to become carbon dioxide.Green plants absorb the carbon dioxide, so the population of carbon-14 molecules is continually replenished until the plant dies.Fossils document the order of appearance of groups and they tell us about some of the amazing plants and animals that died out long ago.Fossils can also show us how major crises, such as mass extinctions, happened, and how life recovered after them.Carbon-14 has a half-life of 5,730 ± 40 years, meaning that every 5,700 years or so the object loses half its carbon-14.Samples from the past 70,000 years made of wood, charcoal, peat, bone, antler or one of many other carbonates may be dated using this technique.Repeated recalibrations and retests, using ever more sophisticated techniques and equipment, cannot shift that date. With modern, extremely precise, methods, error bars are often only 1% or so.The fossil record is fundamental to an understanding of evolution.
After death the amount of carbon-14 in the organic specimen decreases very regularly as the molecules decay.These demonstrate that, of course, we do not know everything (and clearly never will), but we know enough.Today, innovative techniques provide further confirmation and understanding of the history of life.Though still heavily used, relative dating is now augmented by several modern dating techniques.Radiocarbon dating involves determining the age of an ancient fossil or specimen by measuring its carbon-14 content.
Early geologists, in the 1700s and 1800s, noticed how fossils seemed to occur in sequences: certain assemblages of fossils were always found below other assemblages. Since 1859, paleontologists, or fossil experts, have searched the world for fossils.