Dating Notes Donald’s 101 to Dating

Earth Science Trivia If you were contracted to construct a timeline of the Earth’s history What are at least 2 things that you would have to study to create the time scale? What type of scientist could you be? Rock Layers and Fossils Paleontologist (studies fossils) or Geologist (studies rocks)

Why is Geological Dating Important in Science? To know when an organism existed and construct a history of prehistoric Earth! Geological Time Scales are made by piecing together the fossil record

The Fossil Record Paleontologists group similar organisms together Structure Habitat Location They also arrange organisms in the order in which they lived, from earliest to latest

Geologic Time Scale A CHRONOLOGICAL record of the life forms and geological events in Earth’s history Developed from studying ROCK LAYERS and INDEX FOSSILS

But, How Do Scientists Know How Old Something is??? Through the use of 2 dating techniques Relative Dating Determining the order of events by examining the positions of rock layers Absolute Dating Determining the age, in years, of an event through the use of technological tools and tests

Relative Dating Relies on the Principle of Superposition! Remember…oldest rocks are the bottom layer etc. etc. etc. Used for giving the ORDER of events ONLY (this is older than this, this is younger than that) Will NOT tell an exact age in years

Relative Dating UNCONFORMITIES ONE PROBLEM Most rock layers are not pristine (they have been disturbed) Uplift, rock layer tilting and EROSION angle and remove rock layers causing GAPS in the fossil record known as… UNCONFORMITIES

Unconformity Angular Unconformity - Result when horizontal layers lie on top of tilted layers

Unconformity Disconformity /Nonconformity - Results when top rock layer is eroded away BEFORE a new layer is deposited = GAP in record

So what do we really use this for? Correlation of rock layers To identify gaps called… UNCONFORMITIES To help us understand early Earth and continental positioning This means we have to study land ALL aver the world!

Absolute Dating Relies on atoms and their radioactive decay Assigns a number in years to the event

Important Vocab Radioactive Decay: When an atom releases energy as it changes to a new kind of atom Isotope: An atom of the same element with a different number of neutrons Parent Material: Original isotope (pre-decay)

Important Vocab Daughter Material: What the parent becomes as it decays Half Life: The time it takes for HALF of the radioactive atoms to decay Page 347: Using Math 5 lives have past, 5 x 1600 = 8000 years

Absolute Dating Radiometric Dating Age calculation from measuring the parent to daughter material ratio and applying the elements half life Types Carbon - 14 Potassium - Argon

Absolute Dating Carbon - 14 Dating: Carbon-14 decays to nitrogen-14 ALL plants and animals contain carbon Scientists measure the amount of carbon-14 left in the remains Carbon-14 half life is 5730 years

C - 14 Problems EXPENSIVE Difficult Accuracy Recent = 200 year span Older = 500-1000 year span EXPENSIVE Difficult Sample - Only useful for dating once living materials UP TO 50,000 years old

Sample Problems Homework!

Summary Geologic Dating is important because… Two types of dating are… Relative dating is… Absolute Dating is… They are different because…