A shellfish alive today in a lake within a limestone catchment, for instance, will yield a radiocarbon date which is excessively old.The reason for this anomaly is that the limestone, which is weathered and dissolved into bicarbonate, has no radioactive carbon.Evidence from radiometric dating indicates that Earth is about 4.54 billion years old.The geology or deep time of Earth's past has been organized into various units according to events which took place in each period.
Museum paleontologist Tom Deméré, who was involved in the excavation and has also been part of this study, said the project took five months and covered almost 600 square feet.
This clock representation shows some of the major units of geological time and definitive events of Earth history.
The Hadean eon represents the time before fossil record of life on Earth; its upper boundary is now regarded as 4.0 Ga (billion years ago).
SYNONYMS OR RELATED TERMS: morphological type; morphology CATEGORY: typology DEFINITION: A descriptive and abstract grouping of individual artifacts whose focus is on overall similarity rather than specific form or function.
SYNONYMS OR RELATED TERMS: typology CATEGORY: technique DEFINITION: The classification of artifacts into types to compare artifacts or features across time and space, or to determine relative dates for sites.