chapter 8: history of life on earth -...

Chapter 8: History of Life on Earth

Objectives for the Chapter: 1. Summarize how radioisotopes can be used to determine Earth's age. 2. Compare 2 models that describe how the chemicals of life organized. 3. Describe how cellular organization might have begun. 4. Recognize the importance that a mechanism for heredity has to the development of life. 5. Distinguish between 2 groups of prokaryotes. 6. Describe the evolution of eukaryotes. 7. Recognize an evolutionary advance first seen in protists. 8. Summarize how mass extinctions have affected the evolution of life on Earth. 9. Relate the development of ozone to the adaptation of life on land. 10. Identify the first multicellular organisms to live on land. 11. Name the first animals to live on land. 12. List the first vertebrates it leave the oceans.

Vocabulary

Radiometric dating Radioisotope

Half-life Fossil

Cyanobacteria Eubacteria

Archaebacteria Endosymbiosis

Protist Extinction

Mass extinction Mycorrhizae Mutualism Arthropod Vertebrate

Continental drift

Assignment: Using the picture on the front cover, hypothesize what you think the Earth conditions were like 4.5

billion years ago.

15 points

Vocabulary

Radiometric dating Radioisotope

Half-life Fossil

Cyanobacteria Eubacteria

Archaebacteria Endosymbiosis

Protist Extinction

Mass extinction Mycorrhizae Mutualism Arthropod Vertebrate

Continental drift

Assignment: Using the picture on the front cover, hypothesize what you think the Earth conditions were like 4.5

billion years ago.

15 points

The Age of the Earth

When the Earth formed, about 4.5 billion years ago, it was a fiery ball of molten rock. Eventually, the planet's surface cooled and formed a rocky crust. Water vapor in the atmosphere condensed to form the vast oceans. Most scientists think life first evolved in these oceans and all life evolved from there. By measuring the age of objects, we can get a measurement of Earth's age. This is called radiometric dating (the measurement of an object's age by measuring its content of radioactive isotopes). An isotope is a form of an element whose atomic mass differs from that of other atoms of the same element. Radioactive isotopes, or radioisotopes, are unstable isotopes that break down and give off energy in the form of radiation. The radiation is measured and compared to the amount of time it takes for that element to decay completely. The time it takes for 1/2 of a given amout of a radioisotope to decay is called its half-life. Scientists can then compute how many half-lives have past since the rock was formed.

Formation of the Basic Chemicals of Life

Most scientists think life on Earth developed through natural chemical and physical processes. Discussion of 2 models, on the next page, will help us better understand this.

The Age of the Earth

When the Earth formed, about 4.5 billion years ago, it was a fiery ball of molten rock. Eventually, the planet's surface cooled and formed a rocky crust. Water vapor in the atmosphere condensed to form the vast oceans. Most scientists think life first evolved in these oceans and all life evolved from there. By measuring the age of objects, we can get a measurement of Earth's age. This is called radiometric dating (the measurement of an object's age by measuring its content of radioactive isotopes). An isotope is a form of an element whose atomic mass differs from that of other atoms of the same element. Radioactive isotopes, or radioisotopes, are unstable isotopes that break down and give off energy in the form of radiation. The radiation is measured and compared to the amount of time it takes for that element to decay completely. The time it takes for 1/2 of a given amout of a radioisotope to decay is called its half-life. Scientists can then compute how many half-lives have past since the rock was formed.

Formation of the Basic Chemicals of Life

Most scientists think life on Earth developed through natural chemical and physical processes. Discussion of 2 models, on the next page, will help us better understand this.

In the 1920s, A.I. Oparin and J.B.S. Haldane suggested that the Earth's oceans contained large amounts of organic molecules, like soup is filled with many different vegetables and meat. They hypothesized that these molecules formed spontaneously in chemical reactions activated by the sun, volcanic eruptions, and lightning.

Along with Harold Urey, they also proposed the Earth's atmosphere lacked oxygen. Instead, it was rich in nitrogen gas, hydrogen gas, water vapor, ammonia, and methane. In 1953, scientist Stanley Miller tested their hypothesis by placing all the above gases in an apparatus (on the next page) and used electricity sparks to mimic lightning. He found simple organic molecules could be formed this way.

Reevaluating the Miller-Urey ModelRecent discoveries have caused scientists to reevaluate the Miller-Urey experiment. We now know that the reductant molecules used in their experiment could have not existed in abundance on early Earth. 4 billion years ago the Earth did not have a protective layer of gas, ozone. Without ozone, UV radiation would have destroyed any ammonia or methane present in the atmosphere. When these gases are absent from the Miller-Urey experiment, organic molecules cannot be made. So where did they come from?

The "Primordial Soup" Model

In the 1920s, A.I. Oparin and J.B.S. Haldane suggested that the Earth's oceans contained large amounts of organic molecules, like soup is filled with many different vegetables and meat. They hypothesized that these molecules formed spontaneously in chemical reactions activated by the sun, volcanic eruptions, and lightning.

Along with Harold Urey, they also proposed the Earth's atmosphere lacked oxygen. Instead, it was rich in nitrogen gas, hydrogen gas, water vapor, ammonia, and methane. In 1953, scientist Stanley Miller tested their hypothesis by placing all the above gases in an apparatus (on the next page) and used electricity sparks to mimic lightning. He found simple organic molecules could be formed this way.

Reevaluating the Miller-Urey ModelRecent discoveries have caused scientists to reevaluate the Miller-Urey experiment. We now know that the reductant molecules used in their experiment could have not existed in abundance on early Earth. 4 billion years ago the Earth did not have a protective layer of gas, ozone. Without ozone, UV radiation would have destroyed any ammonia or methane present in the atmosphere. When these gases are absent from the Miller-Urey experiment, organic molecules cannot be made. So where did they come from?

The "Primordial Soup" Model

The Bubble Model

In 1986, Louis Lerman suggested that they key processes that formed the chemicals needed for life took place within the bubbles on the ocean's surface. Find the steps to the process below.

Precursors of the First CellsScientists disagree about the details of the process that led to the origin of life, but most have accepted under certain conditions, the basic molecules of life form spontaneously. The question is, since the process can not be duplicated in a laboratory setting, where did the first chain of RNA, eventually making DNA, come from?

Thomas Cech believed RNA molecules can act as enzymes which provides a surface in which chemical reactions can occur on. He hypothesized RNA was the first self-replicating information-storage molecule and it catalyzed the assembly of the first proteins. In 1989, he received a Nobel Prize Award for his work.

Although many scientists disagree about the details of the origin of heredity, many agree double-stranded DNA evolved after RNA. Each day more and more experiments and evidence collection is taking place and a single, new discovery could lead scientists to the answer.

The Bubble Model

In 1986, Louis Lerman suggested that they key processes that formed the chemicals needed for life took place within the bubbles on the ocean's surface. Find the steps to the process below.

Precursors of the First CellsScientists disagree about the details of the process that led to the origin of life, but most have accepted under certain conditions, the basic molecules of life form spontaneously. The question is, since the process can not be duplicated in a laboratory setting, where did the first chain of RNA, eventually making DNA, come from?

Thomas Cech believed RNA molecules can act as enzymes which provides a surface in which chemical reactions can occur on. He hypothesized RNA was the first self-replicating information-storage molecule and it catalyzed the assembly of the first proteins. In 1989, he received a Nobel Prize Award for his work.

Although many scientists disagree about the details of the origin of heredity, many agree double-stranded DNA evolved after RNA. Each day more and more experiments and evidence collection is taking place and a single, new discovery could lead scientists to the answer.

Assignment: Answer the following

questions and email your responses to

[email protected]. The subject of the email

should be Chapter 8, Assignment 1.

1. Explain how radioisotopes are used to determine the age

of a rock. 2. Critique 2 scientific models that explain the origin of life. 3. Describe the first step that

may have lead to cellular organization.

10 points

The Evolution of ProkaryotesWhen did the first organisms form? To find out, scientists study the best evidence of early life forms: fossils. Fossils are the preserved or mineralized remains or imprints of and organism that lived long ago. Recall, prokaryotes are single-celled organisms that lack internal organelles. Among the first to appear were marine Cyanobacteria. Cyanobacteria are photosynthetic prokaryotes that can produce their own energy. The beginnings of oxygen on Earth is credited to them. Through photosynthesis, oxygen was produced as a by-product. Eventually, enough oxygen was produced to form our ozone and to allow organisms to revolve outside of water.

2 Types of Prokaryotes1. Eubacteria - prokaryotes that contain peptidoglycan in their cell walls. Many eubacteria cause disease and decay. 2. Archaebacteria - prokaryotes that lack peptidoglycan in their cell walls. They have uniques lipids in their cell membranes.

Assignment: Answer the following

questions and email your responses to

[email protected]. The subject of the email

should be Chapter 8, Assignment 1.

1. Explain how radioisotopes are used to determine the age

of a rock. 2. Critique 2 scientific models that explain the origin of life. 3. Describe the first step that

may have lead to cellular organization.

10 points

The Evolution of ProkaryotesWhen did the first organisms form? To find out, scientists study the best evidence of early life forms: fossils. Fossils are the preserved or mineralized remains or imprints of and organism that lived long ago. Recall, prokaryotes are single-celled organisms that lack internal organelles. Among the first to appear were marine Cyanobacteria. Cyanobacteria are photosynthetic prokaryotes that can produce their own energy. The beginnings of oxygen on Earth is credited to them. Through photosynthesis, oxygen was produced as a by-product. Eventually, enough oxygen was produced to form our ozone and to allow organisms to revolve outside of water.

2 Types of Prokaryotes1. Eubacteria - prokaryotes that contain peptidoglycan in their cell walls. Many eubacteria cause disease and decay. 2. Archaebacteria - prokaryotes that lack peptidoglycan in their cell walls. They have uniques lipids in their cell membranes.

Th Evolution of Eukaryotes Eukaryotes began appearing about 1.5 billion years ago. Recall, eukaryotes are organisms that have organelles in their cells, like a nucleus and mitochondria. Other eukaryotes, like plants and protists, have chloroplasts. Many biologists think that those organelles (mitochondria and chloroplasts) originated through a theory called endosymbiosis. This theory was proposed by Lynn Margulis in 1966 and states mitochondria are the descendants of symbolic, aerobic eubacteria and chloroplasts are the descendants of symbiotic, photosynthetic eubacteria.

Multicellularity

Many biologists group all living things into 6 broad categories called kingoms. The 2 oldest kingdoms are eubacteria and archaeabacteria that are sometimes grouped together in a kingdom called Monera. The first eukaryotic kingdom was the kingdom Protista, which includes all protists. This kingdom includes both single-celled and multicellular organisms. The development of multicellular organisms was an important milestone in the evolution of life. The other 3 kingdoms, Plantae, Animalia, and Fugi, evolved later.

Th Evolution of Eukaryotes Eukaryotes began appearing about 1.5 billion years ago. Recall, eukaryotes are organisms that have organelles in their cells, like a nucleus and mitochondria. Other eukaryotes, like plants and protists, have chloroplasts. Many biologists think that those organelles (mitochondria and chloroplasts) originated through a theory called endosymbiosis. This theory was proposed by Lynn Margulis in 1966 and states mitochondria are the descendants of symbolic, aerobic eubacteria and chloroplasts are the descendants of symbiotic, photosynthetic eubacteria.

Multicellularity

Many biologists group all living things into 6 broad categories called kingoms. The 2 oldest kingdoms are eubacteria and archaeabacteria that are sometimes grouped together in a kingdom called Monera. The first eukaryotic kingdom was the kingdom Protista, which includes all protists. This kingdom includes both single-celled and multicellular organisms. The development of multicellular organisms was an important milestone in the evolution of life. The other 3 kingdoms, Plantae, Animalia, and Fugi, evolved later.

Origins of Modern OrgansismsMost animal phyla that exists today originated during a relatively short time during the late Precambrian and early Cambrian periods. This rapid diversification of animals is sometimes known as the "Cambrian Explosion.". In 1909, scientists uncovered a multitude of fossils in the Burgess Shale in Canada. Many of the fossils found were from strange organisms not alive today. For example, a Trilobitie, which is a marine organism.

Assignment: Answer the following questions

and email responses to [email protected]. The subject of the email should be

Chapter 8, Assignment 2.

1. Contrast 2 major groups of prokaryotes.

2. Explain Margulis's theory of endosymbiosis.

3. Compare bacteria with eukaryotes.

4. Justify the argument that today's organisms would not

exist if mass extinctions had not occurred.

10 points

Mass ExtinctionsThe fossil record indicates throughout Earth's history there has been periods where all of a single species dies (extinction) and also other times when many species die at the same time (mass extinction). 5 total mass extinctions have occurred in the past and scientists think we are currently in our 6th mass extinction. This is because the Earth's ecosystems are being destroyed hand over fist for human development and advancement.

1. Contrast 2 major groups of prokaryotes.

2. Explain Margulis's theory of endosymbiosis.

3. Compare bacteria with eukaryotes.

4. Justify the argument that today's organisms would not

exist if mass extinctions had not occurred.

10 points

Mass ExtinctionsThe fossil record indicates throughout Earth's history there has been periods where all of a single species dies (extinction) and also other times when many species die at the same time (mass extinction). 5 total mass extinctions have occurred in the past and scientists think we are currently in our 6th mass extinction. This is because the Earth's ecosystems are being destroyed hand over fist for human development and advancement.

Life Invaded the LandThe first multicellular organisms to live on land may have been fungi living together with plants or algae. Such paired organisms were able to live on land because each group possessed a quality needed by the other.

Early plants and fungi formed a biological partnership called mycorrhizae which enabled them to live in rocky environments. Fungus provides minerals and plants provide energy.

This kind of relationship is called mutualism. In a mutualistic relationship, both species benefit. Plants and fungi began living together on land about 430 million years ago.

Arthropods After 100 million years of fungi and plant union, the Earth was covered in dense forests. Theses forests were able to provide a food source not yet seen on our planet, paving the way for land-dwelling animals. The first of those animals were the Arthropods. An arthropod is an animal with a hard outer skeleton, a segmented body, and paired, jointed limbs. Examples include lobsters, crabs, insects, and spiders.

A unique kind of terrestrial arthropod -the insect- evolved the ability to fly. They have grown to become the most plentiful and diverse group of animals in Earth's history.

Life Invaded the LandThe first multicellular organisms to live on land may have been fungi living together with plants or algae. Such paired organisms were able to live on land because each group possessed a quality needed by the other.

Early plants and fungi formed a biological partnership called mycorrhizae which enabled them to live in rocky environments. Fungus provides minerals and plants provide energy.

This kind of relationship is called mutualism. In a mutualistic relationship, both species benefit. Plants and fungi began living together on land about 430 million years ago.

Arthropods After 100 million years of fungi and plant union, the Earth was covered in dense forests. Theses forests were able to provide a food source not yet seen on our planet, paving the way for land-dwelling animals. The first of those animals were the Arthropods. An arthropod is an animal with a hard outer skeleton, a segmented body, and paired, jointed limbs. Examples include lobsters, crabs, insects, and spiders.

A unique kind of terrestrial arthropod -the insect- evolved the ability to fly. They have grown to become the most plentiful and diverse group of animals in Earth's history.

FishesFishes were among the first of the vertebrates (organisms with a backbone) on our planet. The first of their kind were the jawless fishes which appeared 530 million years ago. Jawed fishes followed about 430 million years ago. In the beginning, vertebrates stayed in the oceans, but eventually evolved the ability to live outside of water. Fishes are the most abundant and successful living vertebrates today. They make up over 1/2 of all living vertebrates.

AmphibiansAmphibians appeared 370 million years ago as the first vertebrates to live out of the sea.

Their characteristics included smooth skin, 4 legs, skeleton for walking, and lungs. Examples are frogs, newts, salamanders, and toads. Even though they adapted to lie outside the water, amphibians need a moist environment to live in.

FishesFishes were among the first of the vertebrates (organisms with a backbone) on our planet. The first of their kind were the jawless fishes which appeared 530 million years ago. Jawed fishes followed about 430 million years ago. In the beginning, vertebrates stayed in the oceans, but eventually evolved the ability to live outside of water. Fishes are the most abundant and successful living vertebrates today. They make up over 1/2 of all living vertebrates.

AmphibiansAmphibians appeared 370 million years ago as the first vertebrates to live out of the sea.

Their characteristics included smooth skin, 4 legs, skeleton for walking, and lungs. Examples are frogs, newts, salamanders, and toads. Even though they adapted to lie outside the water, amphibians need a moist environment to live in.

Mammals and Birds

Birds evolved from featured dinosaurs during or after the Jurassic period. Therapsids gave raise to mammals about the same time dinosaurs evolved. Birds have sophisticated flight, eggs with hard shells, and feathers. Mammals have mammary glands, hairs, and teeth. Humans evolved later with growing intelligence.

Reptiles

Reptiles evolved from amphibians about 340 million years ago. Examples include snakes, lizards, turtles, and crocodiles. Reptiles are better suited for dry environment because they have scaled skin that traps moisture and they lay water-tight eggs.

Mammals and Birds

Birds evolved from featured dinosaurs during or after the Jurassic period. Therapsids gave raise to mammals about the same time dinosaurs evolved. Birds have sophisticated flight, eggs with hard shells, and feathers. Mammals have mammary glands, hairs, and teeth. Humans evolved later with growing intelligence.

Reptiles

Reptiles evolved from amphibians about 340 million years ago. Examples include snakes, lizards, turtles, and crocodiles. Reptiles are better suited for dry environment because they have scaled skin that traps moisture and they lay water-tight eggs.

1. Summarize why ozone was important in enabling life on

land. 2. Name the first multicellular organisms that colonized land.

3. Identify the first kinds of animals to live in land.

4. Describe the first kinds if vertebrates that inhabited land.

10 points

End of Chapter 8

1. Summarize why ozone was important in enabling life on

land. 2. Name the first multicellular organisms that colonized land.

3. Identify the first kinds of animals to live in land.

4. Describe the first kinds if vertebrates that inhabited land.

10 points

End of Chapter 8

chapter 8: history of life on earth -...

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