1. The document discusses methods for dating rocks, including relative dating techniques based on stratigraphy and principles like superposition, as well as absolute dating using radiometric methods like radiocarbon, potassium-argon, and uranium-lead dating. 2. It explains key concepts in stratigraphy like how stratified rocks are formed through deposition of sediments in horizontal layers. The principles of superposition, original horizontality, cross-cutting relationships, inclusions, and fossil succession allow geologists to determine the relative ages of stratified rocks. 3. Absolute dating methods like radiocarbon, potassium-argon, uranium-lead, and rubidium-strontium dating determine the numerical ages of rocks by measuring the decay of

1. Earth Science
Quarter 2- Module 5
Dating the Earth

2. Objectives
At the end of the lesson, the learners will be able to:
1.DESCRIBE HOW STRATIFIED ROCKS ARE FORMED;
2.DESCRIBE THE DIFFERENT METHODS OF
DETERMINING THE AGE OF STRATIFIED ROCKS.

3. Concept
Map.

4. The Greek philosopher, Aristotle (384-322 BC), thought
that the Earth was in perpetual existence. The Roman poet,
Lucretius (15 BC to 99 BC), believed that the earth had not
existed for a long time based on the absence of accounts
prior to the Trojan war. One of the famous assumptions
came from James Ussher of Ireland, who believed that the
time of creation of the earth was 4004 BC. It was in the
1660s when Nicolas Steno, a Danish anatomist and a
priest, formulated the modern concepts of deposition of
horizontal strata. In the 1700s, James Hutton, a Scottish
geologist, proposed the principle of uniformitarianism
which states that the physical, chemical, and biological
processes that work today are the same forces that have
worked in the geologic past.

5. Relative Age
Relative dating is used to arrange geological events, and the
rocks they leave behind, in a sequence. The method of
reading the order is called stratigraphy (layers of rock are
called strata). Relative dating does not provide actual
numerical dates for the rocks. Sedimentary rocks have
bedding, a kind of planar feature in the rock. A layer of
sedimentary rock that is visually separable from other layer is
a bed or stratum/ strata.
How Stratified rocks are formed?
Stratification is a layered structure formed by the
deposition of sedimentary rocks. Changes between strata are
interpreted as the result of fluctuations in the intensity and

6. the depositional agent, e.g., currents, wind, or waves, or in
changes in the source of the sediment.
Stratigraphic Law
Stratigraphy is the study of strata, or sedimentary layers. The
principle of original horizontality states that sedimentary layers
are deposited horizontally or nearly so. The basic principles
considered by geologist in relating rocks to Earth’s history are;
1. Principle of superposition
states that in an undisturbed
sequence of stratified rocks,
each layer is older than the
one above it and younger than
the one below it.

7. 2. Principle of original horizontality
states that sediments that are
deposited in flat layers. Thus, if the
rock still maintains its horizontal
layers, it means that it is not yet
disturbed and still has its original
horizontality
3. Principle of cross-cutting
relationships states that when a fault
or a dike – a slab of rock that cuts
through another rock – or when
magma intrudes to the rock, that
fault or magma intrusions is younger
than the rock.

8. 4. Principle of inclusion states that a
rock mass that contains pieces of
rocks, called inclusions, is younger
than other rock masses.
5. Principle of fossil succession ( also
known as the law of faunal succession),
states that organisms evolve in a definite
order, that species evolve and become extinct,
never to re-‐evolve. Thus the evolution of
species and its extinction become time
markers separating time into three units one
before the organisms existed, one during the
existence of the organisms, and one after the
organism went extinct. Index, or guide fossils
are organisms that existed for a short period
of time, and then went extinct.

9. 6. Principle of unconformities states
that rock layers that formed without
interruption. Although there are
sections or strata that are considered
conformable, no place on Earth is
completely free from interruptions as
the rock layers are deposited. An
unconformity is a boundary between
rocks of distinctly different ages where
rocks were either deposited and then
eroded, or simply not deposited.
What is Absolute Dating?
Absolute dating is commonly used for methods of determining numerical
ages of rocks. It is also known as isotopic dating or radiometric dating. This
uses natural radioactive decay to measure the age of rocks by determining the
half-life of the radioisotope present in the rock. Half-life is the length of time it

10. takes half of the radioactive parent isotope of one element to decay into the
new daughter isotopes of another element. It gives rocks an actual date or
date range in number of years. Notice that absolute here does not denote
precise or accurate. This means that an absolute date may have error given
with a plus-or minus (±) sign, which indicates the range of possible values.
Radiocarbon dating is the use of the decay of carbon-14, an isotope of
carbon, to date events in the past. It can give ages of sedimentary rocks with
fossils because fossils have carbon. It involves reactions with carbon.
Carbon-14 has a short half- life compared to the age of many rocks and
cannot be used if the sample is over 70,000 yr. For rocks older than 70,000
yrs., isotopic dating generally applies to igneous and metamorphic rocks. We
can, however, combine isotopic and relative dating. Using what we call
indirect dating.
Different elements have different half-lives, ranging from fractions of a
second to billions of years. This is shown in the table below.

11. Table 1. Common Radioactive Isotopes used in Radiometric dating and their Half-
lives
Name of
Dating
System
Radioacti
ve Isotope
(Parent)
Used for
Dating
Rocks
Symb
ol of
paren
t
Isotop
e
Daughter
Isotope
Symbol
of
Daught
er
Isotop
e
Half
-life
Age
Rang e
Rock Type
Carbon-
14 dating
Carbon-14 14C Nitrogen-
14
14N 573
0 yr.
±30
100
and 70,00
0 yrs.
Sedimenetary
Potassiu
m-argon
dating
Potassium
-40
40K Argon-40 40Ar 1.3
Byr.
50,00
0 yr
to 4.6 Byr
Igneous/metamorphic
Uranium-
Lead dating
Uranium-
238
238U Lead-206 206Pb 4.56
Byr
10 M
to 4.6 Byr
Igneous/metamorphic
Uranium-
235
Uranium-
235
235U Lead-207 207Pb 704
Myr
10 M
to 4.6 Byr
Igneous/metamorphic
Rubidium
-strontium
dating
Rubidium-
87
87R Strontiu
m-87
87Sr 48.8
Byr
10 M
to 4.6 Byr
Igneous/metamorphic

12. Exercise 1. Relative Dating
Direction: Answer the following questions on a separate sheet of paper.
1.Use stratigraphic superposition to list the order of formation of the
sedimentary and volcanic rocks Fig. 7, from oldest to youngest.
___________________________________________________________
2.Does the principle of inclusions give the same results for D as stratigraphic
superposition?
___________________________________________________________

13. Exercise 2.
Direction: Identify the words described by the following phrases. Write
your answer in a separate sheet of paper.
_______________1. It states that a rock mass that contains pieces
of rocks, called inclusions, is younger than other rock
masses.
_______________2. It means that organisms evolve in a definite
order, that species evolve and become extinct, never to re-
evolve.
_______________3. These are organisms that existed for a short
period of time, and that went extinct.
_______________4. It states that rock layers that formed without
interruption.

14. _______________5. It states that when a fault or a dike – a slab
of rock that cuts through another rock.
______________ 6. These are sediments that are deposited in flat
layers.
______________ 7. It states that in an undisturbed sequence of
stratified rocks, each layer is older than the one above it and
younger than the one below it.
______________ 8. It is the study of strata, or sedimentary
layers.
______________ 9. A method used to arrange geological events,
and the rocks they leave behind, in a sequence.
____________ 10. This is a layered structure formed by the
deposition of