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8th Grade Science:

T.2

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IXL brings 8th grade science to life! Set students up for success with thousands of skills that challenge learners at just the right level.

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This interactive module allows students to explore the science of Earth's deep history, from its formation 4.5 billion years ago to modern times.

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EarthViewer | This interactive module allows students to explore the science of Earth's deep history, from its formation 4.5 billion years ago to modern times.

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Fossil Dig

Topics Covered: Fossils, the law of superposition, evidence, evolution, transitional fossils, radiometric dating, absolute vs. relative dating, sedimentation and sedimentary rock formation, how igneous rock is used in radiometric dating.
Credits: Fossil images adapted from here with permission: Image by brgfx on Freepik

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Video computer games, virtual labs and activities for learning and reviewing biology content. Great for students and teachers.

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Fossils 101 educational video clip

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Fossils are echoes of an ancient past. Find out about the two major categories of fossils, how fossilization occurs, and how fossils can help paint a picture of the planet's history.

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Copy of the scale used in class

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Learning Module about the Law of Superposition

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The law of superposition is one of the most fundamental laws in the fields of geology and archeology. This ScienceStruck article explains the law of superposition, and explores its significance.

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What Does the Law of Superposition Mean?

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The law of superposition is one of the most fundamental laws in the fields of geology and archeology. This ScienceStruck article explains the law of superposition, and explores its significance.

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Informative Webpage Regarding Superposition and Uniformitarianism

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The Principles of Geology | Marcellus Community Science

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The principle of uniformitarianism states that processes that alter the earth's crust are the same processes that occurred millions of years ago. Furthermore, the results of processes today are the same as the results of the same processes millions of years ago.

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Fossils, Rocks, and Time Informative Webpage

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We study Earth's history by studying the record of past events that is preserved in the rocks. The layers of the rocks are the pages in our history book.
Most of the rocks exposed at the surface of Earth are sedimentary--formed from particles of older rocks that have been broken apart by water or wind. The gravel, sand, and mud settle to the bottom in rivers, lakes, and oceans. These sedimentary particles may bury living and dead animals and plants on the lake or sea bottom. With the passage of time and the accumulation of more particles, and often with chemical changes, the sediments at the bottom of the pile become rock. Gravel becomes a rock called conglomerate, sand becomes sandstone, mud becomes mudstone or shale, and the animal skeletons and plant pieces can become fossils.

An idealized view of a modern landscape and some of the plants and animals that could be preserved as fossils.

Originations of major life forms.

As early as the mid-1600's, the Danish scientist Nicholas Steno studied the relative positions of sedimentary rocks. He found that solid particles settle from a fluid according to their relative weight or size. The largest, or heaviest, settle first, and the smallest, or lightest, settle last. Slight changes in particle size or composition result in the formation of layers, also called beds, in the rock. Layering, or bedding, is the most obvious feature of sedimentary rocks.
Sedimentary rocks are formed particle by particle and bed by bed, and the layers are piled one on top of the other. Thus, in any sequence of layered rocks, a given bed must be older than any bed on top of it. This Law of Superposition is fundamental to the interpretation of Earth history, because at any one location it indicates the relative ages of rock layers and the fossils in them.

Layered rocks form when particles settle from water or air. Steno's Law of Original Horizontality states that most sediments, when originally formed, were laid down horizontally. However, many layered rocks are no longer horizontal. Because of the Law of Original Horizontality, we know that sedimentary rocks that are not horizontal either were formed in special ways or, more often, were moved from their horizontal position by later events, such as tilting during episodes of mountain building.

Rock layers are also called strata (the plural form of the Latin word stratum), and stratigraphy is the science of strata. Stratigraphy deals with all the characteristics of layered rocks; it includes the study of how these rocks relate to time.

Outcrop of the Ordovician Lexington Limestone, which is rich in fossil shells, near Lexington, Kentucky. These horizontally layered beds were deposited about 450 million years ago. The dark stains on the rocks are formed by water seeping from springs. The vertical marks on the rocks are drill holes in which dynamite charges were exploded to remove the rock so that an interstate highway could be built. Photograph courtesy of O.L. Karlkins.

Nearly vertical limestone beds that were disturbed from their original horizontal position by mountain building. The men are collecting Silurian fossil shells. These rocks are in the Arbuckle Mountains, near Ardmore, Oklahoma. Photograph courtesy of J.E Repetski.

This page is URL: https://pubs.usgs.gov/gip/fossils/rocks-layers.html
Last updated 14 August 1997 (krw)
Maintained by John Watson

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Fossils, Rocks, and Time: Rocks and Layers

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We study Earth's history by studying the record of past events that is preserved in the rocks. The layers of the rocks are the pages in our history book. Most of the rocks exposed at the surface of Earth are sedimentary --formed from particles of older rocks that have been broken apart by water or wind.

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Geologic Time Quiz Game

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Free gamified quizzes on every subject that students play in class and at home. Pick an existing quiz or create your own for review, formative assessment, and more.

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Test your knowledge of the geologic time scale :)

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Geological Eons and Eras Diagram | Quizlet

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Start studying Geological Eons and Eras. Learn vocabulary, terms, and more with flashcards, games, and other study tools.

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Radioactive Dating Game

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Learn about different types of radiometric dating, such as carbon dating. Understand how decay and half life work to enable radiometric dating. Play a game that tests your ability to match the percentage of the dating element that remains to the age of the object.