Exam 11: Geologic Time

Numerical dates based on radioactivity are very important for studying Precambrian geologic history because fossils are rare or absent.

A major difference between Catastrophism and Uniformitarianism is ________.

Paleozoic Mesozoic Phanerozoic Cenozoic

Which of the following is an essential characteristic of an index fossil?

The subdivision of the geologic time scale that represents the longest time span is called a(n)________.

In the last few years improvements in technology have allowed geologists to date single grains of some minerals in rocks.A geologist separates 5 grains of the mineral zircon,which can be dated by the Uranium-lead method,and the crystal retains parent and daughter through weathering,erosion,and deposition.Thus,dating each mineral grain only gives the age of the source rock that was eroded,to produce that sand,from which the zircon grain is derived.The 5 grains yield ages of 160,110,2020,66,and 162 million years.What do these ages tell you about the age of the sedimentary strata?

The Morrison Formation is exposed in the western United States and represents a nonmarine deposit with abundant dinosaur fossils.Much of the Morrison is pure mudstone,yet it is common to find highly polished pebbles and cobbles in the mud.Which of the following do you think is the best explanation of these cobbles?

After two half-lives,there is no longer any of the original radioactive material remaining.

The era known as the "age of mammals" is the ________ era.

What term denotes blocks of older rock enclosed in a body of younger igneous rock?

Which of the following denotes the divisions of the geologic time scale in correct order of decreasing lengths of time beginning with the longest time interval and ending with the shortest?

In the late 1800's various principles (original horizontality,inclusions,cross cutting relations,etc.arête)were established and used to ________.

Assume that you have just examined several flat-lying sedimentary layers.After much study you determine that there is a considerable span of time for which no sedimentary rock layer exists at this site.You have just discovered a(n)________.

The geologic time scale was devised before numerical dating using radioactivity was invented.

We now live in the ________ era.

The principle of horizontality which states that sediments are usually deposited in relatively flat layers is important because ________.

The principle of lateral continuity proposes that sedimentary rock layers continue in all directions until they grade into a different rock type or thin out on the edge of a basin is important because ________.

Which of the following is not a very long-lived,radioactive isotope?

What general term denotes a buried,erosional surface where rock layers are missing?

Little Johnnie from down the street from your house brings an object that looks like a bone,and Johnnie says "look,I found a dinosaur bone." Which of the following would not be useful in evaluating Johnnie's claim?