HISTORY OF THE EARTH Fluorine dating:
Bones from fossils absorb fluorine from the
4,567,000,000 years ago, Earth was covered in
groundwater. The amount of fluorine absorbed
molten lava. Earth was completely unrecognizable. In its
indicates how long the fossil has been buried in the
earliest stage of formation, it was inhabitable as it
sediments.
clumped from a cloud of dust.
II. Absolute Dating
Since about 1,000,000,000 years ago, Earth had
its first signs of life. Single-celled organisms consumed ➤ It determines the age of a rock/object using
the sun’s energy. As a waste product, these radiometric techniques.
cyanobacteria eventually filled the oceans and ➤ Absolute dating is quantitative.
atmosphere with oxygen. ➤ This technique helps determine the exact age of the
Next, an oxygenated atmosphere paved the remains.
way for more complex life forms to exist. At about ➤ It
100,000,000 years ago, dinosaurs roamed the Earth is
until their abrupt extinction. more
Finally, 10,000,000 years ago was the age of
mammals. And these mammals are our direct
ancestors. It was only 100,000 years ago when homo
sapiens truly evolved.
specific than relative dating.
➤ Absolute dating is expensive and time-consuming.
➤ It works best for igneous and metamorphic rocks.
Radiometric dating:
This technique solely depends on the traces of
radioactive isotopes found in fossils. The rate of decay
of these elements helps determine their age, and in
I. RELATIVE DATING turn the age of the rocks.
➤ It determines if an object/event is Dendrochronology:
younger or older than another object/event Each tree has growth rings in its trunk. This
from history. technique dates the time period during which these
➤ Relative dating is qualitative. rings were formed.
➤ This technique helps determine the
relative age of the remains. Thermoluminescence:
➤ It is less specific than absolute dating. It determines the period during which certain
➤ Relative dating is comparatively less object was last subjected to heat. It is based on the
expensive and time-efficient. concept that heated objects absorb light, and emit
➤ It works best for sedimentary rocks electrons. The emissions are measured to compute the
having layered arrangement of sediments. age.
Cross dating: Amino acid dating:
This method compares the age of remains or Physical structure of living beings depends on
fossils found in a layer with the ones found in other the protein content in their bodies. The changes in this
layers. The comparison helps establish the relative age content help determine the relative age of these fossils.
of these remains.
Archaeologists and paleontologist rely on
stratigraphy to provide context to their findings during
the excavation process. They can accurately determine
the history of various animals dating back to historical
and pre-historical periods.
Principles of Stratigraphy
Depositional Succession
Sedimentary rocks
deposited as beds or horizons in rock units
record and preserve depositional events
III. STRATIGRAPHY AND THE PRINCIPLES OF
beds often discontinuous
RELATIVE DATING
beds can be eroded or lost
Stratigraphy
result: a gap in the temporal record known as an
The study of stratified rocks is known as
unconformity or hiatus
stratigraphy.
It is a branch of geology that deals with the
correlation, interpretation, and description of Unconformities
stratified sediments and rocks that are found on
Characteristic Features:
or below the surface of the earth.
• Distinct change in rock type, age, orientation or
Stratigraphy is a science that primarily deals
structure
with the study of layered sedimentary rocks
(called strata) but may also include layered
igneous rocks.
Stratigraphy is an important field of modern
archaeology.
Importance of Stratigraphy
Stratigraphy deals with different periods of
geological past by revealing their details from the
beginning to the present period. It is, therefore, an Laws Governing Stratigraphic Relationships
important field in explain various environmental effects
and how they shaped our present. Nicolaus Steno- In 1669, Niels Stensen (1638-1686),
better known then and now by his Latinized name
Stratigraphy enables us to understand the Nicolaus Steno, formulated a few basic rules that
details of geography, climate, glaciations, orogeny, helped him make sense of the rocks of Tuscany and the
epeirogeny, and how the various factors affected the various objects contained within them. His short
evolution and migration of plants and animals. preliminary work, De Solido Intra Solidum Naturaliter
Contento — Dissertationis Prodromus(Provisional report
Through stratigraphic analyses, scientists and on solid bodies naturally embedded in other solids),
geologists are provided with valuable clues about the included several propositions that have since become
age of the earth and its history. These findings are used fundamental to geologists studying all kinds of rocks.
in a myriad of other scientific fields and disciplines Three of these are known as Steno's principles, and a
ranging from city planners, prospecting geologists, fourth observation, on crystals, is known as Steno's
petrologists, and engineers. Law.
• Superposition • Younger units cross-cut older units
relative ages from sequence of rock deposition erosion surfaces
• Initial Horizontality intrusions
orientation of beds when deposited Unconformities
• Lateral Continuity Recorded Sequence of Events:
spatial correlation of individual horizons and rock units 1. Deposition of fossiliferous sediments (A)
• Cross-Cutting Relationships 2. Folding (deformation) of A
sequence of events records in rock relationships 3. Intrusion of igneous rock (B)
Law of Superposition 4. Erosion to create surface (C)
-Order of Layered Units 5. Deposition of fossiliferous sediments (D)
• Definition:
- A rock unit is younger than the one below and
older than the one above
• Stratigraphic Column
- temporal succession of rock units
- deposition not necessarily continuous,
but sequential
Law of Initial Horizontality
Constraints on Original Orientation
• Sediments are deposited as horizontal beds
• Principle applies to sedimentary rocks formed in an
aqueous environment
Evidence of Deformation
• Non-horizontal sedimentary rocks
• Modified by post-depositional events, e.g. folding
Law of Lateral Continuity
Spatial Relationships
Sediments form as continuous layers
Individual horizons or layers thin or end only when
the environment of deposition changes
Enables correlation of beds with specific
characteristics
Cross-Cutting Relationship
Event Sequence
