Relative and Absolute Dating and Marker Fossils in Geologic Time

Summary

This 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

00:00

🌏 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.

05:01

📊 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.

Keywords

💡Relative Dating

Relative dating is a method used by geologists to determine the age of rocks and the order of geological events without necessarily determining their absolute age. It involves comparing the ages of different rock layers or the fossils they contain. In the video, relative dating is discussed as a technique that helps in understanding the sequence of geological events, such as the order in which rock layers were formed.

💡Absolute Dating

Absolute dating is the process of determining an exact age or date for a rock or fossil, usually in years. It is often done through methods like radiometric dating, which uses the decay rates of radioactive isotopes. The video mentions that the age of the Earth is based on radioactive isotopic dating of meteorites, highlighting the importance of absolute dating in establishing a timeline for Earth's history.

💡Marker Fossils

Marker fossils are fossils that are distinctive and occur in the rock record in a short, limited time span. They are used by geologists to correlate rock layers across different regions and to determine the relative age of the rocks. The video emphasizes the use of marker fossils in defining periods of geologic time, as they can indicate a specific time period and help in creating a more detailed geological timeline.

💡Rock Record

The rock record refers to the preserved history of the Earth's crust, which is recorded in the layers of rock. It is not a complete record, as some events may not leave a trace or may be erased over time. The video discusses how the rock record provides evidence for the history of life on Earth and is essential for understanding the geologic time scale.

💡Fossil Record

The fossil record is the part of the rock record that contains evidence of past life, including preserved remains or traces of plants and animals. It is a crucial source of information for understanding evolution and the history of life on Earth. The video highlights the fossil record as evidence for Charles Darwin's theory of evolution, showing an increase in complexity of life over time.

💡Geologic Time Scale

The geologic time scale is a system of chronological measurement used by geologists to describe the timing and relationships of events that have occurred during Earth's history. It is divided into a hierarchy of units based on significant events in Earth's history. The video explains that the geologic time scale is based on the rock record and is used to understand the subdivisions of Earth's long history.

💡Nicolas Steno

Nicolas Steno was a 17th-century Danish scientist who is considered one of the founders of geology. He formulated principles such as the law of superposition, which states that in a sequence of undisturbed sedimentary rocks, the oldest layer is at the bottom and the layers get progressively younger as you go up. The video mentions Steno as one of the first to recognize the correspondence between rocks and time.

💡Stratigraphy

Stratigraphy is the study of rock layers, particularly the order and relationships of strata. It is a fundamental discipline in geology and is used to understand the history of the Earth and the evolution of life. The video discusses stratigraphy as the basis for understanding the rock record and the geologic time scale.

💡Biostratigraphy

Biostratigraphy is a subdiscipline of stratigraphy that uses fossils to correlate and establish the relative ages of rock layers. It is particularly useful in dating rocks where other methods may not be applicable. The video mentions biostratigraphy as a method that deals with the use of fossils to determine the age of rocks.

💡Index Fossils

Index fossils are a specific type of marker fossil that are used to identify and define the boundaries of geologic time periods. They are typically widespread, easily identifiable, and have a short geological time range. The video explains that index fossils are distinctive and can be used to define periods of geologic time.

💡Radiometric Dating

Radiometric dating is a technique used to date rocks and minerals based on the decay rates of naturally occurring radioactive isotopes. It provides numerical dates for the geologic time scale and is essential for absolute dating. The video mentions radiometric dating as the method used to assign numerical dates to the geologic time scale.

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