Photosynthesis is the primary process by which carbon moves from the atmosphere into living things. Research has been ongoing since the s to determine what the proportion of 14 C in the atmosphere has been over the past fifty thousand years. Geologists measure the abundance of these radioisotopes instead to date rocks. The Holocene , the current geological epoch, begins about 11, years ago when the Pleistocene ends. China hosts 20 million years of early Cretaceous era fossils, including amazingly detailed fossils of feathered dinosaurs, like the Sinosauropteryx, which sported short, bristle-like feathers. Together with stratigraphic principles, radiometric dating methods are used in geochronology to establish the geological time scale. Carbon dating is used by archeologists to date trees, plants, and animal remains; as well as human artifacts made from wood and leather; because these items are generally younger than 50, years.


The age of fossils can be determined using stratigraphy, biostratigraphy, and radiocarbon dating. Paleontology seeks to map out how life evolved across geologic time. A substantial hurdle is the difficulty of working out fossil ages. There are several different methods for estimating the ages of fossils, including:. Paleontologists rely on stratigraphy to date fossils. Stratigraphy is the science of understanding the strata, or layers, that form the sedimentary record. Strata are differentiated from each other by their different colors or compositions and are exposed in cliffs, quarries, and river banks. These rocks normally form relatively horizontal, parallel layers, with younger layers forming on top. Because rock sequences are not continuous, but may be broken up by faults or periods of erosion, it is difficult to match up rock beds that are not directly adjacent. Fossils of species that survived for a relatively short time can be used to match isolated rocks: this technique is called biostratigraphy. For instance, the extinct chordate Eoplacognathus pseudoplanus is thought to have existed during a short range in the Middle Ordovician period.

A child mummy is found high in the Andes and the archaeologist says the child lived more than 2, years ago. How do scientists know how old an object or human remains are? What methods do they use and how do these methods work? In this article, we will examine the methods by which scientists use radioactivity to determine the age of objects, most notably carbon dating. Carbon dating is a way of determining the age of certain archeological artifacts of a biological origin up to about 50, years old.

It is used in dating things such as bone, cloth, wood and plant fibers that were created in the relatively recent past by human activities. For example, every person is hit by about half a million cosmic rays every hour. It is not uncommon for a cosmic ray to collide with an atom in the atmosphere, creating a secondary cosmic ray in the form of an energetic neutron, and for these energetic neutrons to collide with nitrogen atoms.

When the neutron collides, a nitrogen seven protons, seven neutrons atom turns into a carbon atom six protons, eight neutrons and a hydrogen atom one proton, zero neutrons. Carbon is radioactive, with a half-life of about 5, years. For dating your ex step information on cosmic rays and half-life, as well as the process of radioactive decay, see How Nuclear Radiation Works.

Animals and people eat plants and take in carbon as well. The ratio of normal carbon carbon to carbon in the air and in all living things at any given time is nearly constant. Maybe one in a trillion carbon atoms are carbon The carbon atoms are always decaying, but they are being replaced by new carbon atoms at a constant rate. At this moment, your body has a radiocarbon dating is used for estimating the ages of percentage of carbon atoms in it, and all living plants and animals have the same percentage.

The ratio of carbon to carbon at the moment of death is the same as every other living thing, but the carbon decays and is not replaced. The carbon decays with its half-life of 5, years, while the amount of carbon remains constant in the sample. By looking at the ratio of carbon to carbon in the sample and comparing it to the ratio in a living organism, it is possible to determine the age of a formerly living thing fairly precisely.

So, if you had a fossil that had 10 percent carbon compared to a living sample, then that fossil would be:. Because the half-life of carbon is 5, years, it is only reliable for dating radiocarbon dating is used for estimating the ages of up to about 60, years old. However, the principle of carbon dating applies to other isotopes as well.

Potassium is another radioactive element naturally found in your body and has a half-life of 1. The use of various radioisotopes allows the dating of and geological samples with a high degree of continue reading. However, radioisotope dating may not work so well in the future.

Anything that dies after the s, when Nuclear bombsnuclear reactors and open-air nuclear tests started changing things, will be harder to date precisely. How Carbon is Made. Dating a Fossil. Lots More Information. Geological Survey's Publication "Geotime". Related Content " ". What will Earth look like in 5, years? What's the difference between stalactites and stalagmites?