Kysymyksiä

Dating Methods

Most people agree with the concept that the universe is very old but not everyone. If you have read any creation scientist literature or visited such websites you may be taken aback at some of the bold claims that are made that the earth is only 6,000 - 10,000 years old. To someone who does not have a background in science the creation "scientists" can sound quite convincing. So in the interest of true science and reason here is a little background about the tools that educated minds have used to accurately determine the age of the earth and universe.

Absolute Dating Methods

Radio Carbon Dating

In 1949 an American chemist Willard Libby discovered the radioactive charcoal contained in organic materials could be measured. Living plants absorb radioactive C14 from the atmosphere. The plant grows through photosynthesis using carbon dioxide. Three isotopes are produced from carbon. C12 and C13 are stable. C14 is unstable and decays. The rate of decay is known. C14 is being produced continuously in the atmosphere's upper layer while the C14 produced in the past is decaying. The unstable C14 is in proportion to the stable C12. Living creatures ingest and store up the C14 in their bodies. When a living creature dies the intake of C14 ceases and the decay of C14 proceeds at a known rate. The half-life of a substance is the time it takes for half of the substance to decay. The half-life of C14 is 5,570 yrs. It is possible to calculate the time since accumulation of C14 stopped by measuring the remaining C14. This is much like calculating how long a stove burner has been turned off by measuring its temperature. If it is at room temperature it was turned off a long time ago if it is still hot then it was more recently turned off. If an artifact has very little C14 it was "turned off" (died) a long time ago. The radiocarbon dating method works best on items between 500 and 50,000 yrs of age. This dating method can be used on most organic materials such as bone, hair, skins, wood or peat. The method works best on wood and charcoal and less well on bone and other animal artifacts. As this method works very well on wood this provides a means of cross-checking. Trees have have annual growth rings which can be compared to the radiocarbon dating results.The tools to conduct the dating are constantly being refined. With the accelerator mass spectrometric technique only a few milligrams of material are needed to produce reliable results. The radio carbon dating method is limited to artifacts of less than 70,000 yrs of age.

Thermoluminescent Dating

Artifacts are exposed to sunlight or heated by fire, trapping electrons. When the artifact is buried the electrons are released over time. The light emitted by residual electrons is compared to the original exposure to light allowing the calculation of the time since the object was buried. This dating method extends back to 100,000 years so it can date artifacts too old to be read by radiocarbon dating. It can also be used to cross check with radio carbon dating artifacts less than 70,000 yrs. of age

Potassium-Argon Dating

Potassium 40 decays into argon gas at a known rate. When a volcano erupts lava the lava cools forming mineral crystals. The argon gas is trapped in the crystals. The relative proportions of Potassium 40 and argon gas are measured. From this the time since the lava was formed can be calculated.

Uranium-Lead Dating

Uranium decays into other elements at a known rate. There are intermediate elements produced which eventually decay into the final elements. There are two main atomic isotopes U235 and U238. They decay at different rates and go through different intermediate steps. These rates are constant. The different rates of decay act as a cross-checking mechanism to make sure the dating is consistent. The range of this dating method can be used to date geological deposits over 4 billion years of age.

Fission-Track Dating

Uranium 235 can undergo spontaneous fission. Tracks are left by the atomic particles in the mineral. Hydrofluoric acid can etch the tracks and they can be counted. The rate at which fission occurs is known and it is possible to calculate the time since the mineral was formed.


Relative Dating Methods

Chemical Methods

The chemical composition of a fossil can change over time. One indicator of a fossil's age is the ammount of fluourine it contains. Another principle that can be utilized is the fact that the amino acids found in living organisms rotate polarized light to the left. When the creature dies the polarization changes and there is eventually the same proportions of left-rotating and right-rotating amino acids. This is called amino racemization. This process is affected by environmental factors so it is only useful under certain controlled conditions such as within a cave that is sealed off.

Varves

Varves are layers of sediment deposited by flowing rivers. Rivers flow faster during certain times of the year usually in spring when snow and ice melt and more sediment can be carried by the raging river. Each layer does not necessarily correspond to a year but there would not be that many summer storms that could produce flooding equal to a sustained high water flow during the spring thaw. It provides a general but not an absolute method to date a geological formation.

Paleomagnetism

The earth's magnetic field swings back and forth over time. Currently it is facing magnetic north but 3/4 of a million years ago it was facing to the south pole. Several hundred thousand years earlier it was to the north pole. This process keeps repeating. A magnetic signature sometimes remains in mineral formations. So by analyzing the direction of the signature the mineral formation can be categorized as to possible time intervals. By cross checking with other available information an accurate determination can be made.

Faunal Dating

This is a general dating system which is by no means absolute. Basically it means dating a fossil site by the evolutionary stage achieved by the fossilized animals. The method is to compare the fossils to fossils of the same species in other sites that are possible to date by absolute methods. For example a hominid skull of a certain cranial capacity can be compared to the cranial capacity of another fossil homid skull in a site that has been absolutely dated. This method of dating can fail if one geographical area evolved the species at a higher or slower rate than the other used for comparison.