2. Integrated Science Unit 10, Chapter 28 3. 28.1 Understanding
Earth *Geologyis the study of rocks and materials that make up
Earth and the processes that shape it. In1666, Nicholas Steno
(1638-87) noticed that sharks teeth resembled mysterious stones
called tonguestones that were found in local rocks. 4. 28.1
Understanding Earth Stenosexplanation helped him develop ideas
about how rocks and fossils form. Theseideas are used in a
technique called relative dating. *Relativedating is a way to put
events in the order inWhat happened here and in what order? which
they happened. 5. 28.1 Understanding Earth *The approximate age of
each layer of a rock formation can be determined by applying Stenos
idea called superposition. A stack of newspapersillustrates
superposition. *Superposition meansthat the bottom layers ofrock
are older than thelayers on the top. 6. 28.1 Understanding Earth
*Original horizontality states that sediment particles fallto the
bottom of a basin, such as a riverbed, in responseto gravity and
result in horizontal layers. 7. 28.1 Understanding Earth *Lateral
continuity is the idea that layers of sedimentextend in all
directions when they form and before theybecome rock layers. The
idea of lateralcontinuity states thatlayers of rock arecontinuous
unless ageologic event like ariver interrupts thelayers or
anearthquake them. 8. Superposition
LateralContinuityOriginalHorizontality 9. 28.1 Understanding Earth
Anotherimportant idea, developed by Scottish geologist James Hutton
(1726-97), is that the "present explains the past." *The idea of
cross- cutting relationships states that a vein of vein rock is
younger than the rock that surrounds a vein. 10. 28.1 Understanding
Earth Sometimes rock pieces called inclusions are containedin
another rock. *During the formation of arock with
inclusions,sediments or melted rocksurrounded the inclusionand then
solidified. *Therefore, the inclusionsare older than thesurrounding
rock. 11. 28.1 Understanding Earth *Over geologic history,many
animals and plantshave lived and becomeextinct. *Their remains
havebecome fossils. *The idea of faunalsuccession states
thatfossils can be used toidentify the relative age oflayers of a
rock formation. 12. 28.1 Calculating Earths Age William Thompson
Kelvin (1824-1907), known for proposing the absolute temperature
scale that came to be named after him, meticulously calculated
Earths age to be between 10 million and 100 million years. Lord
Kelvins calculation was not accurate because he did not realize
that Earth has internal heat from the core and radioactive decay.
13. 28.1 Calculating Earths Age Earths age was estimatedby
measuring theradioactive decay ofuranium to lead. With improved
techniquesand evidence from treerings and glaciers: *The age of
Earth isestimated to be about 4.6billion years. 14. 28.1 The Layers
of the Earth Earths surface is covered with a thin crust. There are
two kinds of crust: continental oceanic 15. 28.1 Convection inside
Earth The rocky material of the mantle moves in very slow
convection currents. This movement is related to density and
temperature differences in the mantle. Hot material is less dense
and rises. Cold material is denser and sinks. 16. Structure of the
Earth: 17. 28.1 Understanding EarthKey Question: What story is
hidden here?*Read text section 28.1 BEFOREInvestigation 28.1
