8.1 Relative and absolute dating methods

Geological dating methods are crucial for understanding Earth's history. They fall into two categories: relative dating, which determines the sequence of events, and absolute dating, which provides specific ages. These methods help geologists piece together the Earth's timeline.

Relative dating uses principles like superposition and cross-cutting relationships to order events. Absolute dating, including radiometric techniques, measures isotope decay to calculate precise ages. Together, these methods reveal the Earth's fascinating geological story.

Geological Dating Methods

Relative vs absolute dating methods

Top images from around the web for Relative vs absolute dating methods

• 

  Overview of Relative and Absolute Dating – Introductory Physical Geology Laboratory Manual ... View original

  Is this image relevant?

• 

  The Geologic Time Scale – Physical Geology Laboratory View original

  Is this image relevant?

• 

  How do scientists date rocks and fossils? — Earth@Home View original

  Is this image relevant?

• 

  Overview of Relative and Absolute Dating – Introductory Physical Geology Laboratory Manual ... View original

  Is this image relevant?

• 

  The Geologic Time Scale – Physical Geology Laboratory View original

  Is this image relevant?

1 of 3

Top images from around the web for Relative vs absolute dating methods

• 

  Overview of Relative and Absolute Dating – Introductory Physical Geology Laboratory Manual ... View original

  Is this image relevant?

• 

  The Geologic Time Scale – Physical Geology Laboratory View original

  Is this image relevant?

• 

  How do scientists date rocks and fossils? — Earth@Home View original

  Is this image relevant?

• 

  Overview of Relative and Absolute Dating – Introductory Physical Geology Laboratory Manual ... View original

  Is this image relevant?

• 

  The Geologic Time Scale – Physical Geology Laboratory View original

  Is this image relevant?

1 of 3

• Relative dating methods determine sequence of events without specific ages based on geological principles and observations providing chronological order of events (Law of Superposition)
• Absolute dating methods provide specific numerical ages for rocks or events utilizing radioactive decay of isotopes measuring time in years (Radiometric dating)

Principles of relative dating

• Principle of superposition states younger layers deposited on top of older layers except in overturned beds or thrust faults
• Principle of original horizontality explains sedimentary layers initially deposited horizontally tilted or folded layers indicate later deformation
• Cross-cutting relationships show features that cut through other rocks are younger applies to intrusions, faults, and unconformities (dikes cutting through bedrock)
• Inclusions demonstrate rock fragments within another rock are older than the host rock used to determine relative age of igneous intrusions (xenoliths in granite)

Radiometric dating fundamentals

• Based on decay of radioactive isotopes in rocks and minerals measures ratio of parent to daughter isotopes
• Half-life concept represents time required for half of parent isotope to decay unique to each isotope
• Common radiometric dating methods include Potassium-Argon dating for volcanic rocks and Uranium-Lead dating for zircon crystals
• Importance in geology provides numerical ages for rocks and events allows calibration of geological time scale crucial for understanding Earth's history and processes

Carbon dating process and applications

• Carbon dating principles based on decay of radiocarbon (Carbon-14) cosmic rays produce C-14 in atmosphere living organisms incorporate C-14 through carbon cycle
• Carbon dating process:
  1. Measure C-14 to C-12 ratio in sample
  2. Compare to known atmospheric ratio
  3. Calculate age using C-14 half-life of 5,730 years
• Applications include dating organic materials up to about 50,000 years old archaeology (artifacts, human remains) paleontology (fossils, ancient plant material)
• Limitations include not suitable for materials older than 50,000 years affected by variations in atmospheric C-14 levels requires calibration with other dating methods