What are some difficulties in dating the geologic time scale

Radiometric Dating and the Geological Time Scale

One difficulty with the time scale is that we can not differentiate fine time increments. Using radioactivity in dating Reviewing basic atomic structure Nucleus —Protons — positively charged particles with mass —Neutrons — neutral particles. My presentations Profile Feedback Log out. Auth with social network: Registration Forgot your password? Determining geological ages Relative age dates — placing rocks and events in their proper sequence of formation Numerical dates. Download ppt "Chapter 9 Geologic Time. About project SlidePlayer Terms of Service. To avoid problems, one safeguard is to use only fresh, unweathered material.

Half-life of only years 2.

Circular Reasoning or Reliable Tools?

Used to date very recent events 3. Carbon is produced in the upper atmosphere. Useful tool for anthropologists, archeologists, and geologists who study recent Earth history. Radiometric dating is a complex procedure that requires precise measurement 2.


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Rocks from several localities have been dated at more than 3 billion years 3. Confirms the idea that geologic time is immense.

Hadean — the oldest eon. Collectively, the Hadean, Archean, and Proterozoic eons are often referred to as the Precambrian. Not divided into smaller time units because the events of Precambrian history are not known in great enough detail. Precambrian rocks have been subjected to a great many changes.

Geologic Time Deciphering Earth History and Time Scale.

The grains composing detrital sedimentary rocks are not the same age as the rock in which they occur b. The age of a particular mineral in a metamorphic rock may not necessarily represent the time when the rock formed. Explain the difference between relative and absolute dating of earth materials. Briefly explain other principles used in relative age dating. List and briefly explain the three types of unconformities. Briefly discuss fossilization, including the origin and types of fossils.

Discuss the correlation of rock layers using physical criteria and fossils. Briefly explain radioactivity and how it relates to absolute age dating.

Geologic Time Scale

Discuss the procedure of radiometric dating and explain how it is used to obtain absolute ages. List the isotopes commonly used in the radiometric dating of earth materials. List and briefly discuss the major subdivisions of the geologic time scale. Briefly explain the significance of the Precambrian division of the geologic time scale. Two types of dates are used in determining geological ages A. Relative dates — placing rocks and events in their proper sequence of formation B.

Earth Science, 12e Geologic Time Chapter 11

Numerical dates — which specify the actual number of years that have passed since an event occurred II. Principles and rules of relative dating A.


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  2. Earth Science, 12e Geologic Time Chapter 11.
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  8. Law of superposition 1. In an undeformed sequence of sedimentary rocks or layered igneous rocks , the oldest rocks are on the bottom B. Principle of original horizontality 1. Rock layers that are flat have not been disturbed C. Principle of cross-cutting relationships — a younger feature cuts through an older feature D.

    One rock unit is enclosed within another Rock containing the inclusions is younger II. An unconformity is a break in the rock record, a long period during which deposition ceased, erosion removed previously formed rocks, and then deposition resumed 1. Types of unconformities a. Angular unconformity — tilted rocks are overlain by flat-lying rocks b. Disconformity — strata on either side are parallel c. Nonconformity — older metamorphic or intrusive igneous rocks in contact with younger sedimentary strata III. Fossil — the remains or traces of prehistoric life B.

    Types of fossils 1. Gastroliths polished stomach stones C. Conditions favoring preservation 1. Possession of hard parts IV.

    Correlation of rock layers A. Matching rocks of similar age in different regions often relies upon fossils 1. William Smith lates—early s noted that sedimentary strata in widely separated areas could be identified and correlated by their distinctive fossil content 2. Principle of fossil succession — fossil organisms succeed one another in a definite and determinable order, and therefore any time period can be recognized by its fossil content V. Dating with radioactivity A. Reviewing basic atomic structure 1. Different mass number than the parent atom B. Types of radioactive decay I. An electron beta particle is given off from the nucleus a Mass number remains unchanged and the atomic number increases by 1 iii.

    Electron capture a An electron is captured by the nucleus b Electron combines with a proton to form a neutron c Mass number remains unchanged and the atomic number decreases by 1 b. Half-life — the time for one-half of the radioactive nuclei in a sample to decay C.