Relative and Absolute Dating and Marker Fossils in Geologic Time
Summary
TLDRThis educational video delves into the methods of determining geological time subdivisions, focusing on relative dating, absolute dating, and the role of marker fossils. It explains the significance of the rock record and its limitations, highlighting how fossils provide evidence for evolution. The video also touches on the contributions of geologists like Nicolas Steno and Abraham Gottlieb Werner to the understanding of geological time, emphasizing the importance of fossils in correlating rock layers and defining geological periods.
Takeaways
- 🌏 The Earth has a 4.6 billion-year history, with the oldest dated rocks being around 3.8 billion years old.
- 🔬 Radioactive isotopic dating of meteorites is used to determine the age of the Earth.
- 🦠 The oldest known fossils are of simple-celled organisms, dating back to 3.8 billion years ago.
- 🌱 The first multicellular organisms evolved around 1 billion years ago.
- 📚 The rock record is the primary source for understanding Earth's history, but it is incomplete and requires interpretation.
- 🔍 Fossils, including their remains and traces, provide evidence for evolution and are crucial for the geologic time scale.
- 🕰 The geologic time scale is divided into eons, eras, periods, and epochs, based on significant Earth events.
- 🎯 Nicolas Steno's principles of superposition, original horizontality, and lateral continuity form the foundation of stratigraphy.
- 🌋 Abraham Gottlieb Werner, a German geologist, was one of the first to subdivide the rock record into time units using the law of superposition.
- 🔬 William Smith observed that each layer of sedimentary rock contains a distinct set of fossils, which can be used to correlate rock units.
- 📊 Index fossils, which are distinctive, widespread, and have a limited time range, are used to define periods of geologic time.
Q & A
What are the two main methods discussed in the script for determining the age of the Earth?
-The two main methods discussed are relative dating, absolute dating, and the use of marker fossils.
How old is the Earth according to the script?
-The Earth is approximately 4.6 billion years old based on radioactive isotopic dating of meteorites.
What is the oldest dated rock from Earth mentioned in the script?
-The oldest dated rock from Earth is about 3.8 billion years old.
When did the first multicellular organisms evolve according to the script?
-The first multicellular organisms evolved around a billion years ago.
What is the rock record and why is it important?
-The rock record is the history of the Earth recorded in rocks. It is important because it provides evidence for the Earth's history, including the evolution of life and significant geological events.
Why is the rock record considered incomplete?
-The rock record is considered incomplete because some events do not leave a record or are not preserved, and some parts of the rock record may have been lost through the recycling of rocks.
What is the significance of fossils in the rock record?
-Fossils in the rock record provide compelling evidence for Charles Darwin's theory of evolution, showing an increase in complexity of life over time.
What is the largest hierarchical interval in the geologic time scale?
-The largest hierarchical interval in the geologic time scale is the eon.
What significant event occurred around 66.4 million years ago?
-A mass extinction event, which led to the extinction of the dinosaurs, occurred around 66.4 million years ago.
Who is Nicolas Steno and what is his contribution to geology?
-Nicolas Steno is one of the first to recognize the correspondence between rocks and time. His principles, namely superposition, original horizontality, and lateral continuity, became the foundation of stratigraphy.
What is the law of superposition and how was it used by Abraham Gottlieb Werner?
-The law of superposition states that within a sequence of layers of sedimentary rocks, the oldest layer is at the base and layers become younger as you go up. Abraham Gottlieb Werner used this law to establish temporal relationships among rock units.
What is the role of index fossils in defining periods of geologic time?
-Index fossils are distinctive, widespread, and have a limited geologic time range, making them useful in defining periods of geologic time by providing a reference point for the age of rock layers.
Outlines
🌏 Understanding Earth's History Through Dating and Fossils
This paragraph delves into the methods used to determine the age of the Earth and its geological history. It introduces the concepts of relative dating and absolute dating, with the Earth's age confirmed at 4.6 billion years through radioactive isotopic dating of meteorites. The oldest rocks on Earth are about 3.8 billion years old, and the oldest known fossils, simple-celled organisms, are found in these rocks. The paragraph emphasizes the importance of the rock record in understanding Earth's history, despite its inherent incompleteness. It also touches upon the significance of fossils in tracing the evolution of life, supporting Darwin's theory of evolution through the observation of increasing complexity over time. The geologic time scale is mentioned as a hierarchical timeline based on significant events interpreted from the rock record, such as mass extinctions like the one that led to the dinosaurs' extinction around 66.4 million years ago.
📊 Geologic Time Scale and Contributions of Pioneering Geologists
Paragraph 2 discusses the contributions of early geologists to the understanding of the geologic time scale. Nicolas Steno's principles of superposition, original horizontality, and lateral continuity are highlighted as foundational to stratigraphy, the study of layered rocks. Abraham Gottlieb Werner, a German geologist, is recognized for his early attempts to subdivide the rock record into primary, secondary, tertiary, and quaternary units, using the law of superposition to establish temporal relationships. William Smith's work in identifying distinct fossil assemblages in different rock strata, which allowed for the correlation of rock units over long distances, is also mentioned. Charles Lyell's approach to using the proportion of living to extinct fossils to subdivide geologic time is briefly touched upon. The paragraph concludes with a mention of index fossils, which are used to define periods of geologic time, and the assignment of numerical dates to the geologic time scale through absolute dating methods like radiometric dating.
Mindmap
Keywords
💡Relative Dating
💡Absolute Dating
💡Marker Fossils
💡Rock Record
💡Fossil Record
💡Geologic Time Scale
💡Nicolas Steno
💡Stratigraphy
💡Biostratigraphy
💡Index Fossils
💡Radiometric Dating
Highlights
Introduction to relative dating, absolute dating, and marker fossils for determining geologic time subdivisions.
The Earth's history spans 4.6 billion years, with the oldest dated rocks at 3.8 billion years old.
Oldest known fossils are of simple-celled organisms from 3.8 billion-year-old rocks.
Multicellular organisms evolved around 1 billion years ago.
The rock record is the primary source for Earth's history but is incomplete and requires interpretation.
Fossils in rocks provide evidence for Darwin's theory of evolution and increasing complexity of life.
Geologic time scale is based on the rock record and is divided into eons, eras, periods, and epochs.
Mass extinction event 66.4 million years ago, pivotal for the rise of mammals.
Activity involving filling a table and creating a pie chart of the geologic time scale.
Nicolas Steno's principles of stratigraphy: superposition, original horizontality, and lateral continuity.
Pie chart represents the relative proportions of major geologic time subdivisions.
Precambrian time, comprising Hadean, Archaean, and Proterozoic eons, is largely mysterious due to incomplete records.
Abraham Gottlieb Werner's early attempts to subdivide the rock record into primary, secondary, tertiary, and quaternary units.
William Smith's use of distinct fossil assemblages to correlate rock strata across distances.
Charles Lyell's recognition of the utility of fossils in subdividing geologic time.
Stratigraphy and its subdiscipline, biostratigraphy, focus on the study of rock layers and correlation using fossils.
Index fossils, as marker fossils, are used to define periods of geologic time and must be distinctive, widespread, and have a limited time range.
The geologic time scale's numerical dates come from absolute dating through radiometric dating of rocks.
Transcripts
hey guys so i am
i'm not back in this video we're going
to talk about
how relative dating absolute dating
and marker fossils were used to
determine the subdivisions of
geologic time
that was a lot the earth has a very long
history
4.6 billion years of history
the age of the earth is based from the
radioactive isotopic
dating of meteorites the oldest dated
rock from the earth is only about
3.8 billion years old
why i don't know
the oldest known fossils are
simple-celled organisms
found in rocks that are 3.8 billion
years old
the first multicellular organism evolves
around million years ago
the history of the earth is recorded in
rocks
which what we call the rock record now
the rock record is not a video
documentary
a large amount of analysis and
interpretation is required
to extract information from rocks but
the rock record is inherently incomplete
some events do not leave a record or are
not
reserved some of the rock record may
have also been lost
through the recycling of rocks right
remember
the rock cycle
now preserve in rocks are fossils or
their mains and traces of plants and
animals
that have lived and died throughout the
earth's history
the fossil record provides scientists
with one of the most compelling evidence
for charles darwin's theory of evolution
this is about increasing complexity of
life
through time right
so the crux of darwin's theory of
evolution focuses
on the elimination of inferior species
gradually over time
through a process called natural
selection
now this figure the geologic time scale
which is the timeline of the history of
the earth
is based on the rock record
time is divided into hierarchical
intervals
the largest being ion followed by
era period and epoch
the subdivisions of geologic time is
based on significant events
in the earth's history as interpreted
from the rock record
the mass extinction which led the
extinction of the dinosaurs
occurred around 66.4 million years ago
now remember this mass extinction event
may have been pivotal
in the race of the dominance of the
mammals
during the cenozoic era i don't
understand
i don't understand
now let's have an activity what you need
to do
is you have to fill this table up
afterwards
you have to make a pie chart with
respect to the geologic time scale
provided in the table are you kidding me
now i'm getting angry i'll give you
five minutes to accomplish this
[Music]
okay so while you're doing this listen
so one of the first
to recognize the correspondence between
rocks and time
is nicolas steno okay
stannis principle namely superposition
original horizontality
and lateral continuity became the
foundation
of stratigraphy again stratigraphy is
the study of
layered rocks so this is the correct
answer okay so remember you have to make
a pie
chart with respect to the geologic time
scale provided in the table
assuming that you have done the pie
chart
this figure shows relative proportion
of the major subdivisions of geologic
time
now if you notice the precambrian
which is the hadiyan archaean and
proterozoic
represents a large part of the geologic
time which is about 87
yet we know very little of what happened
during this period okay so meaning that
record is imperfect or incomplete
one of the earliest attempts to
subdivide the rock record into units of
time
was made by abraham gottlieb werner
a german geologist werner divided the
rock record into the following rock time
units
from oldest to youngest okay
so we have the primary secondary
tertiary
and quaternary werner extensively used
the law of superposition to establish
temporal relationship
among the rock units he states that
within
sequence of layers of sedimentary rocks
the oldest layer is at the base
and layers become younger as it goes off
okay
so if you remember our previous
discussion about this
yes that's it
so i just want you to know that abraham
werner
is also considered to be the father of
german geology and he is also the
proponent
of neptunism what was that
that is the idea that all of the earth's
rocks
were formed from an all-encompassing
ocean
fossils are also useful in determining
relative ages of rocks
while working in a coal mine william
strata smith
observed that each layer or strata of
sedimentary rock
contains a distinct assemblage of
fossils
which can be used to establish
equivalence
between rock units separated by long
distances
moreover he observed that this fossils
succeed
each other vertically in a definite
order
so this figure shows the geological map
of
england and wales and part of scotland
in 1815 okay and this one
is meets 1820 map called
a new geological map of england in wales
which illustrates the complex geology
surrounding bath england so this
figures are from nasa earth observatory
in contrast to william smith who
primarily used
fossils to identify rock players charles
yell
a british lawyer and geologist
recognized
the utility of fossils in subdividing
geologic time on the basis of fossils
he was able to subdivide the tertiary by
examining the proportion of living
versus extinct fossils in the rocks but
the bottom line is
fossils are essential in the subdivision
of the geologic time so this figure
shows the evolution of
life through time the underlying reason
for this definite and orderly succession
of fossils in the rock record
is seriously what the are you doing
organic evolution so we have studied
stratigraphy right as we have said
stratigraphy is a branch of geology
concerned with the study of rock layers
and layering it's primarily used in the
study of sedimentary and layered
volcanic rocks
now a subdiscipline is what we call
biostratigraphy
this deals with the use of fossils in
the correlation and establishments
of the relative ages of rocks
in the next video we're going to study
the geologic time scale
okay it's over we are screwed
now we have this thing called index
fusions so this figure or table
shows some of them index fossils are
marker fossils
used to define periods of geologic time
so ideally index fossils
are distinctive meaning they can easily
be identified
and distinguished from other fossils
they are widespread meaning the
distribution
is not confined to a few locality
and lastly they have limited geologic
time
range meaning they lived
during only one short period of time
ultimately the geologic time scale was
assigned
numerical dates from absolute dating
through the radiometric dating of
rocks
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