Geology is the study of Earth's rocks and materials. Nicholas Steno developed ideas in the 1600s about how rocks and fossils form using the analogy of shark teeth resembling stones found in rocks. These ideas formed the basis for relative dating techniques. Relative dating determines the order events occurred in by applying principles like superposition, original horizontality, lateral continuity, cross-cutting relationships, inclusions, and faunal succession to analyze rock layers and fossils. Earth's age was originally calculated to be between 10-100 million years but is now estimated at 4.6 billion years based on radioactive dating techniques.

1. Chapter 28.1
Understanding Earth
CPO Science
Neistadt

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
shark’s teeth resembled
mysterious stones called
“tonguestones” that were
found in local rocks.

4. 28.1 Understanding Earth
 Steno’sexplanation helped
him develop ideas about how
rocks and fossils form.
 These ideas are used in a
technique called relative
dating.
 *Relative
dating is a way to
put events in the order in What 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
Steno’s idea called superposition.
 A stack of newspapers
illustrates superposition.
 *Superposition means
that the bottom layers of
rock are older than the
layers on the top.

6. 28.1 Understanding Earth
 *Original horizontality states that sediment particles fall
to the bottom of a basin, such as a riverbed, in response
to gravity and result in horizontal layers.

7. 28.1 Understanding Earth
 *Lateral continuity is the idea that layers of sediment
extend in all directions when they form and before they
become rock layers.
 The idea of lateral
continuity states that
layers of rock are
continuous unless a
geologic event like a
river interrupts the
layers or an
earthquake them.

8. Superposition
Lateral
Continuity
Original
Horizontality

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 contained
in another rock.
 *During the formation of a
rock with inclusions,
sediments or melted rock
surrounded the inclusion
and then solidified.
 *Therefore, the inclusions
are older than the
surrounding rock.

11. 28.1 Understanding Earth
 *Over geologic history,
many animals and plants
have lived and become
extinct.
 *Their remains have
become fossils.
 *The idea of faunal
succession states that
fossils can be used to
identify the relative age of
layers of a rock formation.

12. 28.1 Calculating Earth's Age
 William Thompson Kelvin
(1824-1907), known for
proposing the absolute
temperature scale that came to
be named after him,
meticulously calculated Earth’s
age to be between 10 million
and 100 million years.
 Lord Kelvin’s calculation was
not accurate because he did
not realize that Earth has
internal heat from the core and
radioactive decay.

13. 28.1 Calculating Earth's Age
 Earth’s age was estimated
by measuring the
radioactive decay of
uranium to lead.
 With improved techniques
and evidence from tree
rings and glaciers:
 *The age of Earth is
estimated to be about 4.6
billion years.

16. 28.1 The Layers of the Earth
 Earth’s surface is covered with a thin crust.
 There are two kinds of crust:
— continental
— oceanic

18. 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.

19. Structure of the Earth:

20. 28.1 Understanding Earth
Key Question:
 What story is hidden here?
*Read text section 28.1 BEFORE
Investigation 28.1