There are many different and completely dating methods, both radiometric and non-radiometric, for determining the age of objects.
One of the most robust of the non-radiometric dating methods is ice core chronology. Ice cores are used almost exclusively in the fields of paleoclimatology and glaciology. The accumulation of "firns" in snow fields in the high latitudes stores a plethora of information pertaining to past climates. One important aspect of this information is "when" those climatic conditions occurred, thus the chronological aspect of ice cores.
There are several different and completely independent methods used in identifying annual layers in ice cores. Greenland Ice cores go back as far as 100,000 years, while Antarctic ice cores go back as far as 800,000 years. Here is a list of some of the methods and techniques used in dating ice cores:
1. Visual Layers. Visual stratigraphy in ice cores does not count individual layers of snowfall; it utilizes annual layers which have specific properties completely different from individual snowfalls. In the high latitudes where there are six months of sunlight and six months of darkness an annual "firn" is created. Regardless of the number of snowfalls during the time of continuous sunlight, ice crystals become enlarged. Conversely, during winter (no sunlight) they do not enlarge and become more compacted. That is why a "visual" annual layer consists of one dark and one light layer.
2. Electrical Conductivity. Nitric acid is produced in the atmosphere from the reaction of nitrogen, water vapor and UV irradiation during the summer months. This process is absent during the winter months due to the absence of sunlight. Therefore, summer snowfall is much more acidic than winter snowfall. Needless to say, this is an extremely robust method for identifying annual layers. Not only can extreme variations electrical conductivity be measured but pH as well.
3. Dust. Another annual marker is the amount of dust which is measured with laser light scattering. During late winter and early spring there is significantly more dust in the atmosphere than during other months.
4. Trace chemicals. Differences in amounts of trace chemicals containing calcium and sodium also vary significantly between summer and winter.
5. Isotope concentration. The heavy isotopes of oxygen (O-18) and hydrogen (H-2) also known as deuterium fractionate from the atmosphere during the winter months. Therefore, the ratios between O-18 and O-16 are significantly different between winter and summer months. As well, H-2 and H-1 exhibit the same physical characteristic.
6. Cosmogenic nuclides. Another is the concentration of cosmogenic nuclides, specifically C-14, Be-10, and Cl-36. In this method specific events are measured rather than annual layers which are used to synchronize chronologies. These events are due to magnetic disturbances in the Earth's magnetic field which are well known and are not just contained in ice cores but sediments world-wide.
7. Volcanic eruptions. Significant volcanic eruptions occur on average twice a century and eject enormous amounts of volcanic ash into the atmosphere. This dust can be radiometrically dated which are also cross-referenced to annual layer chronologies.
One of the most robust of the non-radiometric dating methods is ice core chronology. Ice cores are used almost exclusively in the fields of paleoclimatology and glaciology. The accumulation of "firns" in snow fields in the high latitudes stores a plethora of information pertaining to past climates. One important aspect of this information is "when" those climatic conditions occurred, thus the chronological aspect of ice cores.
There are several different and completely independent methods used in identifying annual layers in ice cores. Greenland Ice cores go back as far as 100,000 years, while Antarctic ice cores go back as far as 800,000 years. Here is a list of some of the methods and techniques used in dating ice cores:
1. Visual Layers. Visual stratigraphy in ice cores does not count individual layers of snowfall; it utilizes annual layers which have specific properties completely different from individual snowfalls. In the high latitudes where there are six months of sunlight and six months of darkness an annual "firn" is created. Regardless of the number of snowfalls during the time of continuous sunlight, ice crystals become enlarged. Conversely, during winter (no sunlight) they do not enlarge and become more compacted. That is why a "visual" annual layer consists of one dark and one light layer.
2. Electrical Conductivity. Nitric acid is produced in the atmosphere from the reaction of nitrogen, water vapor and UV irradiation during the summer months. This process is absent during the winter months due to the absence of sunlight. Therefore, summer snowfall is much more acidic than winter snowfall. Needless to say, this is an extremely robust method for identifying annual layers. Not only can extreme variations electrical conductivity be measured but pH as well.
3. Dust. Another annual marker is the amount of dust which is measured with laser light scattering. During late winter and early spring there is significantly more dust in the atmosphere than during other months.
4. Trace chemicals. Differences in amounts of trace chemicals containing calcium and sodium also vary significantly between summer and winter.
5. Isotope concentration. The heavy isotopes of oxygen (O-18) and hydrogen (H-2) also known as deuterium fractionate from the atmosphere during the winter months. Therefore, the ratios between O-18 and O-16 are significantly different between winter and summer months. As well, H-2 and H-1 exhibit the same physical characteristic.
6. Cosmogenic nuclides. Another is the concentration of cosmogenic nuclides, specifically C-14, Be-10, and Cl-36. In this method specific events are measured rather than annual layers which are used to synchronize chronologies. These events are due to magnetic disturbances in the Earth's magnetic field which are well known and are not just contained in ice cores but sediments world-wide.
7. Volcanic eruptions. Significant volcanic eruptions occur on average twice a century and eject enormous amounts of volcanic ash into the atmosphere. This dust can be radiometrically dated which are also cross-referenced to annual layer chronologies.
