Dating Fossils

Outcomes:

• • Outline how the absolute and relative age of fossils can be determined.

  • Apply the Law of Superposition to determine the relative age of fossils.

Fossil Age Determination

Paleontology aims to understand how life evolved over time, but determining fossil ages is challenging. Stratigraphy, biostratigraphy, and carbon dating are methods used to estimate the age of fossils.

 Stratigraphy involves analysing layers of rock surrounding a fossil to determine its age. If a fossil is found between two rock layers with known ages, its age is thought to be between those two ages. 

Biostratigraphy matches rocks with particular fossils to other rocks with those fossils to determine age. Carbon dating is used to determine the age of fossils that are less than 60,000 years old and composed of organic materials. Scientists use the half-life of carbon isotopes to estimate the age of the fossil.

Biostratigraphy

Biostratigraphy matches rocks with short-lived species fossils. Eoplacognathus pseudoplanus, extinct chordate, existed in a brief period in the Middle Ordovician era. Rocks with its traces have mid-Ordovician age. Index fossils should be distinctive, globally distributed, and brief in duration. Wrongly dating index fossils leads to false outcomes. 

Relative Dating

Stratigraphy and biostratigraphy provide relative dating, often adequate for studying evolution. Some periods are challenging due to difficulty matching rocks across continents. Family trees can help estimate when lineages appeared. Molecular clocks, estimating branch divergence, assume constant DNA mutation rates but can be inaccurate and imprecise, particularly for the Cambrian explosion. Different approaches may produce varied results. 

Carbon Dating

Radiometric dating and stratigraphy are used to establish the geological time scale. Fossils in beds often lack the needed radioactive elements for radiometric dating. Radiocarbon dating calculates time by comparing the ratio of a radioactive element to its decay products. The rate of decay is measured by the element's half-life. 

Radiometric dating is a way to figure out how old rocks or materials are by looking at the amount of a special kind of element that breaks down over time. Carbon dating is a specific kind of radiometric dating that can only be used for materials that are less than 60,000 years old, like fossils or ancient wood. 

Scientists use the half-life of carbon-14, which is 5,730 years, to estimate how long ago these materials were alive. Carbon dating only works for materials that used to be alive and have carbon in them. 

1. What is the difference between relative and absolute dating methods for fossils?

2. How do scientists use biostratigraphy to date fossils?

3. What is radiocarbon dating, and how does it help determine the age of fossils?

4. How have advancements in technology, such as genetic analysis, helped refine the dating of fossils?

5. How do scientists use the geological time scale to date fossils and determine the history of life on Earth?