The document discusses the history of the Earth and methods used to determine geological timescales. It describes how rocks form records of past events and processes. Early scientists estimated the age of the Earth to be between 24-100 million years based on studies of heat loss and sodium accumulation in oceans. The principle of uniformitarianism states that past and present geological processes were similar. Relative dating methods order events but do not provide absolute ages. Radiometric dating using radioactive isotopes provides absolute ages and was used to construct the geologic timescale in eras, periods, and epochs marked by significant events in Earth's history.

1. HISTORY OF THE EARTH

2. OBJECTIVES:
• Describe how layers of rocks (stratified rocks) are formed;
• Describe the different methods (relative and absolute
dating) to determine the age of stratified rocks;
• Explain how relative and absolute dating were used to
determine the subdivisions of geologic time; and
• Describe how the Earth’s history can be interpreted from
the geologic time scale.

3. ROCKS
THE RECORDERS OF TIME
Rocks are recorders of time
long before humans
invented its concept.
Processes that happened
long ago are preserved in
rocks through which we
interpret the story.

4. HOW OLD IS EARTH?

5. 1897
“Lord Kelvin”
William Thomson, known as Lord Kelvin, was one of the
most eminent scientists of the nineteenth century
Estimated the age of the Earth from conduction and
radiation studies and found it to be around 24-40 million
years.

6. 1901
John Joly
He proposed to calculate the age of the earth from the
accumulation of sodium in the waters of the oceans. He
calculated the rate at which the oceans should have
accumulated sodium from erosion processes, and
determined that the oceans were about 80 to 100 million
years old.

7. 1700S
James Hutton
“The father of Modern Geology”
He published his Theory of the Earth.
He presented his fundamental principle on
uniformitarianism which states that processes operating
today (rivers flowing, volcanoes erupting, etc.) have been
operating since the formation of Earth, albeit at different
rates, and will continue to do so in the future.
Theory of the Earth is summarized by saying that “THE PRESENT IS THE KEY TO THE PAST”.

8. KNOWING THE
AGE EVENTS
Relative age- refers to the order in which events
occurred. (Comparative)
Absolute Age- refers to the age in years. (Entire)

9. RELATIVE DATING
1. Law of Superposition
States that in an undisturbed sequence of
rocks, the oldest strata/ layer will be found
on the bottom of the basin.
is the process of determining if one rock or geologic
event is older or younger than another, without
knowing their specific ages using field observations.
HEAVIEST-DEEPEST-OLDEST
LIGHTEST-SETTELED ON TOP-YOUNGEST

10. RELATIVE DATING
2. Principle of Original
Horizontality
States that sediments will assume a
horizontal manner (due to gravity)
and will assume such orientation
until lithification process preserves it.
is the process of determining if one rock or geologic
event is older or younger than another, without
knowing their specific ages
Lithification, complex process whereby freshly deposited
loose grains of sediment are converted into rock.
Sediments are deposited in flat layers.
If nor disturbed, they maintain original horizontality.

11. RELATIVE DATING
3. Principle of Cross-
cutting Relationships
When faults/fractures cuts through
rocks, the event of faulting/fracturing is
always younger than the rocks it cuts.
is the process of determining if one rock or geologic
event is older or younger than another, without
knowing their specific ages
THERE IS MAGMA INTRUSION.
FAULTS IS YOUNGER THAN THE OTHER LAYERS.

12. RELATIVE DATING
4. Inclusions
Are pieces of rocks contained within
another. In the same way, anything
(mineral, etc.) that is enclosed/
embedded in rocks are older than the
rock unit surrounding it.
is the process of determining if one rock or geologic
event is older or younger than another, without
knowing their specific ages

13. RELATIVE DATING
5. Unconformities
An undisturbed sequence of rocks
would look like horizontal layers
stacked up of each other.
Conformable (of strata in contact)
deposited in a continuous sequence,
and having the same direction of
stratification.
is the process of determining if one rock or geologic
event is older or younger than another, without
knowing their specific ages

14. 5. UNCONFORMITIES
1. ANGULAR UNCOMFORMITIES
Tilted strata overlain by more
horizontal younger strata.

15. 5. UNCONFORMITIES
2. DISCONFORMITY
Are evidence of erosive agents
acting on the surface of rocks
(sometimes forming a soil layer)
which represents a time when
deposition is at a minimum.

16. 5. UNCONFORMITIES
3. NONCONFORMITY
Igneous rocks sometimes
intrudes/cut through layers of
rocks, inserting a younger rock
unit that cuts across older rocks.

17. 5. UNCONFORMITIES
4. PARACONFORMITY
It is the absence of horizon or
strata based on fossil assemblage.
It represents a period of non-
deposition.
paraconformity (plural paraconformities) (geology) A type
of unconformity in which strata are parallel; there is no
apparent erosion and the unconformity surface resembles
a simple bedding plane.

18. IS THE USE OF RECORDS OF RADIOACTIVE DECAY IN
ROCKS.
ABSOLUTE DATING

19. ISOTOPES
Atoms of the same element
(same number of proton) but
with different number of
neutrons.
Will not emit radioactive
particle or will not decay
spontaneously because it
is stable.

20. ISOTOPES
Atoms of the same element
(same number of proton) but
with different number of
neutrons.
Not stable
Will release radioactive particle or
radiation to become stable or what we
called the RADIOACTIVE DECAY.

21. The half-life of a substance
is the time it takes for half of
the substance to decay. The
word "half-life" was first used
when talking about radioactive
elements where the number of
atoms get smaller over time by
changing into different atoms.
A useful concept is half-life (symbol is t1/2),
which is the time required for half of the
starting material to change or decay. Half-lives
can be calculated from measurements on the
change in mass of a nuclide and the time it takes
to occur.

24. Parent- unstable Isotope and radioactive
Daughter- stable element or the decay product

25. HUMAN SKELETON
75% Nitrogen-14
25% Carbon-14
Carbon-14
Half-life= 5730 years
1 half-life=50% Carbon-14 and 50% Nitogen-14
2 half-life=25% Carbon-14 and 75% Nitogen-14
The fossil has undergone two half lives.
2 x 5730= 11,460 years

28. GEOLOGIC TIME SCALE
It is a hierarchical set of divisions describing geologic time.
Serves as the calendar of events in Earth’s history.
Serves as standard timeline used to describe the age of rocks,
fossils and the events that forms them.
Units of time include eon, era, period, epoch and age.

29. EON ERA PERIOD EPOCH
Represents the longest
amount/subdivision of time
Smallest unit in GTS
Accounts for 88 % of Earth’s history
• Proterozoic
• Archena
• Hedean
Means visible life

31. Beginning of the Earth
Forms the
oldest
fossils
Earliest Life
Form-
Bacteria and
blue green
algae

32. • Beginning of
early life
• Pangaea
• Terrestrial Plants

33. • Age of Dinosaurs
• Laurasia and
Godwana

34. • Age of recent life
• Age of mammals
• Rocks are
accessible

35. • Age of
invertebrates like
trilobites and
cephalopodes

36. • Age of fishes
(fishes became
dominant creatures

37. • Carboniferous
period
• Atmospheric
oxygen

38. • Amphibians
• Reptiles
• Conifers plants

39. • Mammals and
Dinosaur

40. • Birds

41. • Extinction of
dinosaurs
• Age of reptiles

43. • Period where
humans evolve

44. a division of time that is
a subdivision of a
period and is itself
subdivided into ages,
corresponding to a
series in
chronostratigraphy.

45. GEOLOGIC TIME SCALE
Is divided into a series of
time intervals according to
significant events in the
Earth’s history such as mass
extinction.
• Change in Climate
• Large volcanic Eruption
• Meteorite/ asteroid
impact

46. REFERENCES: