Download Essential Standard: 8.E.2 Understand the history of Earth and its life

What You Need to Know
Essential Standard: 8.E.2 Understand the history of Earth and its life forms
based on evidence of change recorded in fossil records and landforms.
Clarifying Objective: 8.E.2.2 Explain the use of fossils, ice cores, composition of
sedimentary rocks, faults, and igneous rock formations found in rock layers as
evidence of the history of the Earth and its changing life forms.
Students need to know:
 that a variety of artifacts are used to determine the geological history of
the Earth, as well as how its life forms have changed over time.
-
Ice cores are cylinders of ice that are drilled out of glaciers and polar ice
sheets. Ice cores play an important role in helping scientists to gain an
understanding of the Earth’s history, particularly how earth’s climate has
changed over time. When snow falls it carries with it the compounds that are
in the air at the time. In areas where temperatures are rarely above freezing
(ice sheets and glacial areas), this builds up layer upon layer of compacted
snow which becomes ice. Within these ice layers there is a record of the
atmosphere at the time that the snow creating the ice layers fell.
-
Sedimentary rock makes up about 75% of the rocks on the Earth’s surface.
Sedimentary rocks form on the surface of the Earth, anywhere that sand,
mud, or other types of sediment collect. Scientists can gain an understanding
of Earth’s climate, biological, and geologic history by examining the contents
of different layers of sedimentary rock. Sedimentary rock layers can be
disturbed by igneous rock. This happens when molten rock forces it way up
through the layers above it. This forms igneous rock sections within and
across the sedimentary layers. The sedimentary rock layers must be there
first, therefore the igneous rock intrusions are younger than the layers it cuts
through. Sometime the molten rock will force its way to the surface and
erupt, creating a younger igneous layer at the surface. With time, more
sedimentary layers can form on top of the igneous rock. Igneous rock is
always younger than rock layers it cuts through.
 that a fault is a break in the rocks that make up the Earth’s crust that is
formed due to the movement of rock on either side of the fault.
-
Generally, faults occur where there is movement (a slip) of tectonic plates.
Sudden movement of this type is associated with earthquakes. Students
know that the two main types of faults involve dip slips and strike slips. In a
dip slip, two pieces of land change their vertical position compared to one
another. Afterward, one side of the fault is higher than the other. In a strike
slip, two pieces of land move horizontally.
BOTTOMLINE: Sediments of sand and smaller particles (sometimes containing the remains
of organisms) are gradually buried and are cemented together by dissolved minerals to form
solid rock again. Sedimentary rock buried deep enough may be re-formed by pressure and heat,
1|Page
perhaps melting and recrystallizing into different kinds of rock. These re-formed rock layers may
be forced up again to become land surface and even mountains. Subsequently, this new rock too
will erode. Rock bears evidence of the minerals, temperatures, and forces that created it. Rocks,
fossils, and ice cores show: 1. Life forms have changed over time and 2. Earth’s climate and
surface have changed over time. The Law of Superposition states that each undisturbed rock
layer is older than the layer above it. This law is used to read rock layers. Thousands of layers of
sedimentary rock confirm the long history of the changing surface of the earth and the changing
life forms whose remains are found in successive layers. By studying rocks and fossils, scientists
have developed a geologic time scale which outlines the major divisions of Earth’s history.
Geologists have concluded that all rocks of the crust form in one of three ways: Igneous rocks
are formed by the cooling and hardening of hot molten rock from inside the Earth. Sedimentary
rocks are formed by the hardening and cementing of layers of sediments. The sediments may
consist of rock fragments, plant and animal remains, or chemicals that form on a lake and ocean
bottom. Metamorphic rocks are formed when rocks that already exist are changed by heat and
pressure into new kinds of rocks. A fault is a fracture in the continuity of a rock formation
caused by a shifting or dislodging of the earth’s crust, in which adjacent surfaces are displaced
relative to one another and parallel to the plane of fracture. There are several types of faults.
Reference: North Carolina Department of Public Instruction, Essential Standards:
Grade 8 Science, Unpacked Content, September 2012 Revision,
http://scnces.ncdpi.wikispaces.net/file/view/Unpacked_Content_Grade8Science_Re
visedSeptember2012.docx.pdf/368725266/Unpacked_Content_Grade8Science_Revi
sedSeptember2012.docx.pdf
2|Page