Fossils and Dating Methods (Exam 3)

How old is the Earth?

4.6 billion years old

When did Pangea begin to pull apart into the present continents?

225 million years ago

Who is responsible for Geologic Time and where is it from?

Charles Lyell, Principles of Geology (1830)

What time frame does the Paleozoic Era cover?

540-250mya

What fossils were found in the Paleozoic Era?

Vertebrae fossils (500mya)

• Fish, amphibians, reptiles

• Mammal-like reptiles (250mya)

What time frame does the Mesozoic Era cover?

250mya-65mya

What fossils were found in the Mesozoic Era?

• Dinosaurs

• Mammals in early Mesozoic

• Placental mammals in late Mesozoic

What time frame does the Cenozoic Era cover?

65mya-Present

What are the sub-eras in the Cenozoic Era in order of oldest to newest?

• Paleocene epoch: 65-2mya

• Eocene epoch: 55-34mya

• Oligocene: 34-23mya

• Miocene: 23-5mya

• Pliocene: 5-1.8mya

What time frame does the Quaternary Period cover?

1.8mya-Present

What are the sub-eras in the Quaternary Period in order of oldest to newest?

o   Pleistocene: 1.8mya-10,000 years ago

o   Holocene/Recent: 10,000 years ago-present

What are fossils?

Preserved remains of a long-dead organism

What can fossils reveal based on their Stratigraphic layer?

Can date the fossils/rocks

• Find out when it died/how old it is

What can fossils reveal based on the Associated Fossils found near them?

Clues about habitat/ecosystem

What can fossils reveal based on the Plant Pollen or Leaves found within them?

Reconstruct habitat, what the animal ate

What is Absolute Dating?

Gives you an approximate age estimation in years (ex: fossil A is x years old)

What is Relative Dating?

Puts fossils/artifacts in a chronological order but without an actual date

• Compare to other sites with real dates to figure out ages

What is the Law of Superposition?

-          In undisturbed sedimentary rock or soil layers, the oldest strata are at the bottom and the youngest are on top

What is Paleomagnetism?

Uses polarity of the Earth’s geomagnetic field to establish a chronological timeline

• Normal polarity – directed north

• Reversed polarity – directed south

What is Biostratigraphy?

Use presence of particular species of animal to establish a chronological order

• Compare to other sites with same species and real dates

What is Radioactive Dating?

Uses decay of radioactive atoms

• Radiocarbon dating

• Potassium-argon dating

What do atoms consist of?

• Nucleus composed of protons and neutrons

• Electrons orbit the nucleus

What are Isotopes?

Elements with various numbers of neutrons

• Some unstable – undergo radioactive decay

• Some elements have radioactive and non-radioactive isotopes (Ex: carbon, potassium)

What happens when atoms decay?

Radioactive parent element decays to form a stable daughter element

• Ex: Uranium, the parent element, ultimately decays to the stable daughter element, lead

• Decay rates are uniform. Occur at a constant exponential rate

What is a Half-life?

The time it takes for half the parent element to decay to daughter product

• Each radioactive isotope has unique half-life

What is Carbon-14 Dating?

The measurement of the decay of Carbon-14 to Nitrogen-14

When can Carbon-14 dating be used on a material?

When the material is <70,000 years old

What is the problem with Carbon-14 dating?

Assumes rate of carbon-14 production (and amount of cosmic rays) has been constant over the past 70,000 years

What is the Potassium-Argon Dating method?

Potassium-40 decays to Argon-40

• Used to date volcanic materials

  • Argon-40 released during eruptions, then accumulates after the eruption cools at a known rate, can them be measured to determine age of rock

When can Potassium-Argon dating be used on a material?

When the material being measured is as old as between 100,000 years to 1.25 billion years old

What is the time range of Radiocarbon dating?

What is the time range of Potassium-argon dating?

>100,000 years old