Quarter 4 Week 7 Defining and Identifying Subdivisions of Geologic Time Scale Using Index Fossil.pptx
- 1. ng Subdivisi ons of Geologic Time Scale Using Index Fossils EARTH SCIENCE 11 STEM Nobility Quarter 4
- 3. Fossils Fossils are remains or traces of organisms that lived in the past. They are mostly formed in sedimentary rocks.
- 4. Index Fossils These are fossils used to determine the ages of rock layers wherein the age of the rock it is in can be determined.
- 5. Index Fossils It is the relative age of the rock layers that is identified using index fossils. Relative age means the age of one object compared to the age of another object.
- 6. Index Fossils It is not the exact age that is identified. The relative age of rocks and fossils can be determined using two basic methods: ordering of rock layers and index fossils.
- 7. Characteristics for a fossil to be considered an index fossil. • An organism must have lived only during a short part of Earth’s history. • Many fossils of the organisms must be found in rock layers. • The fossil must be found over a wide area of Earth. • The organism must be unique.
- 8. Characteristics for a fossil to be considered an index fossil. • The shorter time the period a species lived, the better an index it is. Fossils that are found in many rock layers, therefore living long periods of time, do not qualify as index fossils).
- 9. The Geologic Time Scale • is a record of Earth’s history. For example, the extinction of dinosaurs marked the end of Cretaceous period.
- 10. The Geologic Time Scale In creating the geologic time scale, rock layers were correlated by geologists.
- 11. The Geologic Time Scale The relative ages of rocks were determined using Steno’s laws, which state that “older rocks are at the bottom and younger rocks are at the top”.
- 12. The Geologic Time Scale But it was only the order of events that was shown in the early geologic time scale. Not until in the late 1800s when scientists discovered radioactivity that enabled them to determine the exact age of some rocks in years.
- 13. Absolute Dating The method of measuring the direct age measurements of fossils is known as absolute dating.
- 14. The Geologic Time Scale The names indicated in the different periods of the geologic time scale were derived from various origins.
- 15. The Geologic Time Scale Key fossils or type fossils are the other names of index fossil. They are used in defining the periods of geologic time such as, the ages, epochs, periods, and eras in the formal architecture of geologic time.
- 16. The Geologic Time Scale Some of the boundaries of these subdivisions are defined by mass extinction events, like the Permian-Triassic extinction. The evidence for these events is found in the fossil record wherever there is a disappearance of major groups of species within a geologically short amount of time.