Earth & Space Science Chapter 8: Geologic Time

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Questions and Answers

What was the primary basis of Aristotle's explanations for Earth processes and materials?

Religious texts and scriptures

Observation and experimentation

Arbitrary ideas and philosophical beliefs (correct)

Research and collaboration with other scholars

According to Aristotle, what was responsible for the formation of rocks?

The influence of the stars (correct)

The movement of tectonic plates

The actions of ancient humans

Geological processes such as erosion and sedimentation

What was James Usher's contribution to the field of geology?

He proposed the concept of continental drift

He discovered the process of fossilization

He developed a new theory of plate tectonics

He constructed a chronology of human and Earth history (correct)

What was the date that James Usher determined to be the creation of the Earth?

4004 B.C. Signup and view all the answers

What was the impact of Aristotle's explanations on the development of modern geology?

They slowed down the development of modern geology Signup and view all the answers

What is the main goal of geology/earth science?

To understand Earth history Signup and view all the answers

What method is used today to determine numerical dates?

Radiometric dating methods Signup and view all the answers

Who recognized the Principle of Superposition in 1669?

Nicolas Steno Signup and view all the answers

What is the Principle of Original Horizontality?

Layers of sediment are generally deposited in a horizontal position Signup and view all the answers

What can be concluded when a fault cuts through other rocks?

The fault is younger than the rocks affected Signup and view all the answers

What is the Principle of Inclusions?

Rocks adjacent to the one containing the inclusions must have been there first Signup and view all the answers

What is an unconformity?

A long period during which deposition ceased, erosion removed the material, and deposition resumed Signup and view all the answers

What is the purpose of unconformities?

To identify what intervals of time are not represented by the rocks Signup and view all the answers

What type of unconformity consists of folded/tilted sedimentary rocks that are overlain by younger, more flat-lying strata?

Angular unconformity Signup and view all the answers

Who published the Theory of the Earth in 1795?

James Hutton Signup and view all the answers

What principle states that the physical, chemical, and biological laws that operate today also operated in the geologic past?

Uniformitarianism Signup and view all the answers

What idea emerged during the 17th and 18th centuries to fit the rates of Earth processes to the age of the Earth?

Catastrophism Signup and view all the answers

What is the primary way that mountains are shaped, according to Hutton?

Weathering and water Signup and view all the answers

What concept does Hutton's principle of uniformitarianism support?

A very lengthy Earth history Signup and view all the answers

What is the significance of Hutton's work in the context of geologic processes?

He demonstrated that geologic processes can continue over extremely long periods of time Signup and view all the answers

What is the idea that Earth's landscape has been shaped primarily by great catastrophes?

Catastrophism Signup and view all the answers

What is the phrase that summarizes the principle of uniformitarianism?

The present is the key to the past Signup and view all the answers

What happens when an electron is captured by the nucleus?

The atomic number decreases by 1, but the mass number remains unchanged Signup and view all the answers

What is the term used to describe the process of calculating the numerical ages of Earth materials and events?

Radiometric dating Signup and view all the answers

What is the term used to describe the time required for one-half of the radioactive isotopes to decay into the daughter products?

Half-life Signup and view all the answers

What is the ratio of parent to daughter products when a single half-life has occurred?

1:1 Signup and view all the answers

Which radioactive isotope is the most versatile due to its abundance in silicate minerals?

Potassium-40 Signup and view all the answers

What is the age of the oldest rock found on Earth?

4.28 billion years Signup and view all the answers

What is the half-life of carbon-14?

5,730 years Signup and view all the answers

What is the purpose of radiocarbon dating?

To date recent events Signup and view all the answers

Why is the fossil record incomplete and biased?

Because fossilization is contingent upon specific conditions. Signup and view all the answers

What is the term used to describe the division of geologic time into units of varying magnitude?

Geologic time scale Signup and view all the answers

What is the principle of fossil succession?

That fossils are always found in the same order. Signup and view all the answers

What is the main characteristic of index fossils?

They are widespread geographically but limited to a short span of geologic time. Signup and view all the answers

Why can sedimentary rocks rarely be dated using radiometric techniques?

Because they contain particles from many sources Signup and view all the answers

What is radiometric dating used for?

To determine the numerical age of rocks. Signup and view all the answers

What is the result of the spontaneous breakdown of the nucleus in some isotopes?

Radioactivity. Signup and view all the answers

What determines an element's atomic number?

The number of protons in the nucleus. Signup and view all the answers

What is the result of alpha particle emission?

The mass number decreases by 4 and the atomic number decreases by 2. Signup and view all the answers

What is the combination of correlation and radiometric dating used for?

To determine the numerical age of rocks and develop a comprehensive geologic history. Signup and view all the answers

Why are fossils useful in correlating rock units?

Because they are time indicators and can be used to match rocks of similar age in different regions. Signup and view all the answers

What is the significance of William Smith's observation?

That fossil organisms succeed one another in a definite and determinable order, and therefore any time period can be recognized by its fossil content. Signup and view all the answers

What is the term used to describe the study of fossils?

Paleontology Signup and view all the answers

What is the primary purpose of fossils in interpreting the geologic past?

To understand environmental conditions in which the organism lived Signup and view all the answers

What is the process of fossilization where minerals precipitate out of solution and fill in the pores of an organism?

Permineralization Signup and view all the answers

What type of fossil is formed when the hollow spaces created by a mold are filled with mineral matter?

Cast Signup and view all the answers

What is the term used to describe a fossilized piece of dung or stomach contents?

Coprolite Signup and view all the answers

What is the term used to describe the polished stones found in the stomachs of some extinct reptiles?

Gastroliths Signup and view all the answers

What is the term used to describe the break between older metamorphic or igneous rocks and younger sedimentary strata?

Nonconformity Signup and view all the answers

What is the primary condition that must exist to enhance fossilization?

Rapid burial Signup and view all the answers

What type of fossil is formed when fine sediment encases the remains of an organism and pressure squeezes out liquids and gases, leaving a thin residue of carbon?

Carbonization Signup and view all the answers

What is the term used to describe the fossilized remains of an organism's tracks or footprints?

Track Signup and view all the answers

Study Notes

A Brief History of Geology

• Earth processes and materials have been a focus of investigation for centuries • Aristotle's explanations were not based on observation but rather arbitrary ideas, e.g., rocks were created under the "influence" of the stars, earthquakes developed when air in the ground was heated by fires in the Earth, and fossilized fish lived motionless in the Earth until discovered • Aristotle's explanations were continued for centuries, hindering a more modern approach to Earth processes • James Usher constructed a chronology of human and Earth history in the mid-1600s, determining the Earth was created in 4004 B.C. • The idea of catastrophism developed in the 17th and 18th centuries, stating that the Earth's landscape was shaped primarily by great catastrophes • James Hutton published the Theory of the Earth in 1795, proposing the principle of uniformitarianism, which states that the physical, chemical, and biological laws that operate today also operated in the geologic past

Principles of Geology

• Rocks can be viewed as the pages of Earth's history, but many have been removed, destroyed, or modified by the same processes that formed them • Interpreting Earth history is one of the main goals of geology • Scientists who developed the geologic time scale revolutionized how people perceive our planet and think of "time" • Early attempts to determine the Earth's age in the late 1800s and early 1900s were unsuccessful • Today, scientists use radiometric dating methods to determine numerical dates

Principles of Relative Dating

• To understand and apply relative dating techniques, several principles had to be discovered and applied • The principle of superposition states that in an undeformed sequence of sedimentary rocks, each bed is older than the one above and younger than the one below • The principle of original horizontality states that layers of sediment are generally deposited in a horizontal position • The principle of cross-cutting relationships states that when a fault cuts through other rocks or when magma intrudes and crystallizes, we can conclude that the fault or intrusion is younger than the rocks affected • The principle of inclusions states that the rock unit containing the inclusion is the younger of the two

Unconformities

• Unconformities represent a long period during which deposition ceased, erosion removed the material, and deposition resumed • There are three basic types of unconformities: angular unconformity, disconformity, and nonconformity • Angular unconformity consists of folded or tilted sedimentary rocks that are overlain by younger, more flat-lying strata • Disconformity often resembles a bedding plane, and there is little evidence of erosion • Nonconformity separates older metamorphic or igneous rocks from younger sedimentary strata

Fossils: Evidence of Past Life

• Fossils are essential for interpreting the geologic past • The study of fossils is called paleontology • Fossils help scientists understand environmental conditions in which the organism lived • Fossils are crucial in correlating rocks from different locations • There are several ways in which fossilization can occur, including permineralization, molds and casts, carbonization and impressions, and amber

Correlation of Rock Layers

• To develop a geologic time scale for the entire Earth, rocks of similar age in different regions must be matched • Correlation over short distances is relatively easy, but correlation over great distances is far more complex • Correlation of rock units separated by great distances can be accomplished by using fossils • The principle of fossil succession states that fossil organisms succeed one another in a definite and determinable order • Index fossils are widespread geographically but limited to a short span of geologic time

Dating with Radioactivity

• Radiometric dating is a reliable method for determining the numerical ages of Earth materials and events • Radioactive isotopes decay at a fixed rate, and the time required for one-half of the radioactive isotopes to decay into the daughter products is termed the half-life • There are many radioactive isotopes in nature, but five have proven to be very useful in providing radiometric ages • Potassium-40 is the most versatile radioactive isotope due to its abundance in silicate minerals

The Geologic Time Scale

• The geologic time scale is divided into units of varying magnitude: eons, eras, periods, and epochs • The geologic time scale was developed before radiometric dating • The detail of the geologic time scale does not begin until after the Precambrian (4 billion years of Earth history) • The geologic time scale is dynamic, and as new evidence is uncovered, it will be modified to reflect the new conclusions

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Description

Explore the history of geology, from ancient Greek philosophers like Aristotle to modern understanding of earth processes and materials.