Exam 11: Geologic Time

In the late 1700s James Hutton published his important work entitled______.

The principle of cross- cutting relationships which states that a geologic feature that cuts across another feature must be younger than the feature it cuts is important because______ .

One type of fossil that can preserve details of organic soft parts is ______.

When a rock first crystallizes it has unstable isotopes but as of yet no daughter products. After three half- lives, how much total mass has been lost due to decay?

If you observe a nonconformity, you would infer that the region had experienced ______.

Modern geochronology studies recognize that most radiometric dates record a time when a mineral cools below a temperature where the mineral closes to gain or loss of parent and daughter isotopes. This "closure temperature" varies between different minerals and different isotopic systems. This has allowed the absolute dating of sedimentary rocks through dating of single crystals. For example, if a rock is heated above the closure temperature of the rocks constituent minerals, the date of that mineral provides a minimum age. In contrast, if the rock contains a mineral with a closure temperature higher than the maximum temperature reached by the rock, that mineral will retain the age from its source. The mineral zircon dated by U- Pb methods is an example. So, you look at a rock that has Cretaceous fossils in it, but your paleontologist friend looks at them and cannot determine if they are Early or Late Cretaceous in age. The rock contains the mineral apatite, which accumulates through the decay or U and Th, but closes to He loss at temperature of around 75°C. You know from the stratigra section that the rocks were originally buried at least 3km. The local geothermal gradient is about 35°C/km. You obtain an apatite He date of 105 +/- 2 million years. You also date 100 grains of zircon from the rock. The zircons yield dates that range in age from 2.1 billion years to 125 million years. Three different zircon grains yield ages between 125 and 127 million years. You google "cretaceous time scale" and learn that the Cretaceous begins at about 144 million years and ends at about 65 million years ago. The Early Cretaceous ends about 100 million years ago. How old are these sedimentary rocks?

The phrase, "The present is the key to the past," refers to the doctrine of ______ .

James Hutton stated "We have a chain of facts which clearly demonstrates that the materials of the wasted mountains have traveled through the rivers". He was referring to ______.

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

Assume that man's recorded history can be stretched back to 4600 years before the present. This is approximately what fraction of geologic time?

Who is credited with formulating the doctrine of uniformitarianism?

Paleontology is the study of______ .

Assume that you have just examined several flat- lying sedimentary layers. After much study you determine that there is a considerable span of time missing between two of the sedimentary rock layers at this site. You have just discovered an_______.

Examine the words and/or phrases below and determine the relationship among the majority of words/phrases. Choose the option that does not fit the pattern.

By applying the law of superposition,______ dates can be determined.

The principle of inclusions which states that the source of rock fragments found in a unit must be older than the unit with the fragments is important because______ .

Most sedimentary rocks are readily dated by ______methods.

An important tool in understanding the actual numerical dates of past geologic events is______ .

______is an erosional contact between tilted, older strata below and horizontal, younger strata above.

Consider the below diagram of sedimentary layers. We know that the top layer is youngest. Which of the below is not one of the reasons we know this?