In-Depth Notes on Fossil Dating and Mesozoic Life

Determining the Age of Fossils

• Learning Goals
  • Determine relative and absolute ages of fossils using radiometric dating and stratigraphy principles.
  • Explain climate change during the Mesozoic and its relation to continental configurations.
  • Describe broad-scale changes in vegetation over the Mesozoic and their impacts on dinosaur diversification.

Properties of Atoms

• Each element is defined by its atomic number, which is the number of protons.
  • Example: Helium has an atomic number of 2.
• Atomic weight = number of protons + number of neutrons.
  • Example: Helium's atomic weight = 2 (protons) + 2 (neutrons) = 4.

Isotopes

• Isotopes are variants of the same element, differing in neutron count.
• Parent isotopes are unstable and decay into daughter products.

Dating with Radioactivity

• Provides numeric ages, denoted as absolute age dating.
• Uses decay products of radioactive elements in minerals for age determination.

Half-Life

• Definition: The time required for half of the parent isotope to decay into the daughter isotope.
• After one half-life: 50% of the parent has turned into the daughter.
• This information helps calculate the age of the material based on the parent/daughter ratio.

Carbon-14 Dating

• The half-life of Carbon-14 is approximately 5730 years.
• Specimens older than 55,000 years cannot be accurately dated using this method.

Rocks Suitable for Radiometric Dating

• Types of Rocks That Can Be Dated:
  • Igneous rocks (dating time of magma crystallization)
  • Metamorphic rocks (dating time of metamorphism, not the parent rock).

Lithostratigraphy

• Useful for interpreting the relative ages of Earth's layers.

Principle of Superposition

• In undisturbed sediment layers, the sequence is from oldest at the bottom to youngest at the top.

Principle of Cross-Cutting Relationships

• States that a rock or feature (like a dike) that cuts through another is younger than the rock it disrupts.

Principle of Inclusion

• The inclusions (pieces of one rock type within another) are older than the rock that contains them.
• Example: If granite inclusions are present in sandstone, granite is older.

Biostratigraphy

• Use of fossil types in rocks to determine ages and correlate rock sequences over wide areas.
• Fossils can provide relative age markers for dating rocks.

Factors Influencing Mesozoic Climate

• Global climate changes influenced by:
  • Sea level changes
  • Greenhouse gases
  • Volcanic activity
  • Continental configurations
  • Ocean configurations

Measuring Ancient Climate

• Direct measures of ancient climates are unavailable, hence researchers use proxies such as fossils and geochemical signatures to infer past climates.

Changes in Landscape and Flora

• Early Mesozoic landscapes dominated by ferns, lycopsids, and sphenopsids.
• Gymnosperms (naked seeds) and angiosperms (flowering plants) emerged and contributed to diverse ecosystems.
• Angiosperms evolved during the late Mesozoic, which coincides with rapid herbivore dinosaur diversification.

The Diversification of Dinosaurs

• Dinosaurs began to diversify significantly during the Jurassic and Cretaceous periods, influenced by climate and food availability.
• The breakup of Pangea led to geographical isolation and varying evolutionary paths, contributing to the diversification of dinosaur species and vegetation types.

Conclusion

• Overall, fossil dating combines both absolute and relative dating techniques involving atomic properties and geological principles to understand Earth and life’s history, particularly the evolution and diversification of dinosaurs during the Mesozoic era.