Chapter 9 The History of Life on Earth

Evidence of the Past Paleontologists - use fossils to reconstruct the history of life millions of years before humans existed Fossils show us that life on Earth has changed a great deal They also provide us with clues of how those changes occurred Paleontologists - use fossils to reconstruct the history of life millions of years before humans existed Fossils show us that life on Earth has changed a great deal They also provide us with clues of how those changes occurred

Fossils Fossils - are traces or imprints of once living organisms preserved in rock Animals, plants, fungi, and bacteria can be fossilized Fossils are usually formed when a dead organism is covered by a layer of sediment These sediments may be pressed together to form sedimentary rock The rock cycle - the process by which one type of rock changes into another Fossils - are traces or imprints of once living organisms preserved in rock Animals, plants, fungi, and bacteria can be fossilized Fossils are usually formed when a dead organism is covered by a layer of sediment These sediments may be pressed together to form sedimentary rock The rock cycle - the process by which one type of rock changes into another

The Age of Fossils

Relative Dating A cross section of sedimentary rock shows many layers The oldest layers are on the bottom with the newer layers on top If fossils are found in rock, a scientist could examine the sequence of fossils in the order that the organisms existed This is known as relative dating A cross section of sedimentary rock shows many layers The oldest layers are on the bottom with the newer layers on top If fossils are found in rock, a scientist could examine the sequence of fossils in the order that the organisms existed This is known as relative dating

Absolute Dating Absolute dating - when scientists estimate the age of a fossils by measuring the ratio of unstable atoms to stable atoms in a sample If the “strong” force can no longer hold the particles of an atom together, atoms begin to break down This is known as radioactive decay Because different types of atoms break down at different rates (half life), scientists can accurately estimate the age of fossils Half-life - the amount of time it takes half of a radioactive sample to decay Absolute dating - when scientists estimate the age of a fossils by measuring the ratio of unstable atoms to stable atoms in a sample If the “strong” force can no longer hold the particles of an atom together, atoms begin to break down This is known as radioactive decay Because different types of atoms break down at different rates (half life), scientists can accurately estimate the age of fossils Half-life - the amount of time it takes half of a radioactive sample to decay

The Geologic Time Scale Because the length of time is so great from the formation of the Earth to now, scientists use a “calendar” to divide Earth’s history into smaller units of time Geologic time scale - the “calendar” scientists use to outline the history of life on Earth After a fossil has been dated, a paleontologist can place the fossil in chronological order with other fossils Because the length of time is so great from the formation of the Earth to now, scientists use a “calendar” to divide Earth’s history into smaller units of time Geologic time scale - the “calendar” scientists use to outline the history of life on Earth After a fossil has been dated, a paleontologist can place the fossil in chronological order with other fossils

Divisions in the Geologic Time Scale Paleontologists have divided the time scale into large blocks of time called Eras Each era is characterized by the type of animal that dominated the Earth at that time i.e. the Mesozoic area was dominated by dinosaurs and reptiles The end of each era is marked by the extinction of certain organisms Each era has been subdivided into smaller blocks called Periods Paleontologists have divided the time scale into large blocks of time called Eras Each era is characterized by the type of animal that dominated the Earth at that time i.e. the Mesozoic area was dominated by dinosaurs and reptiles The end of each era is marked by the extinction of certain organisms Each era has been subdivided into smaller blocks called Periods

Mass Extinctions Mass extinctions - periods of large-scale extinctions Extinct - when a plant or animal species completely dies out Scientists are not sure what causes mass extinctions They may result from major changes in the Earth’s climate or atmosphere What do scientist believe caused the extinction of the dinosaurs? Mass extinctions - periods of large-scale extinctions Extinct - when a plant or animal species completely dies out Scientists are not sure what causes mass extinctions They may result from major changes in the Earth’s climate or atmosphere What do scientist believe caused the extinction of the dinosaurs?

Section 2: Eras of the Geologic Time Scale Precambrian time - a time prior to 540 million years ago Only very primitive organisms existed Most did not have hard body parts so there are not many fossils from this era Precambrian time - a time prior to 540 million years ago Only very primitive organisms existed Most did not have hard body parts so there are not many fossils from this era

The Early Earth Life began on Earth under conditions that were very different than today's This included: 1) a lack of oxygen in the atmosphere 1a) the air consisted mostly of carbon monoxide, carbon dioxide, hydrogen, and nitrogen 2) meteors continually crashed into the Earth’s surface 3) there were thunderstorms and constant volcanic eruptions 4) intense radiation from the sun Life began on Earth under conditions that were very different than today's This included: 1) a lack of oxygen in the atmosphere 1a) the air consisted mostly of carbon monoxide, carbon dioxide, hydrogen, and nitrogen 2) meteors continually crashed into the Earth’s surface 3) there were thunderstorms and constant volcanic eruptions 4) intense radiation from the sun

How Did Life Begin? Under harsh conditions life developed from nonliving matter Life began from the chemicals that already existed These chemicals included water, clay, minerals, etc. The energy present causes these chemicals to react, forming the complex molecules that made life possible Under harsh conditions life developed from nonliving matter Life began from the chemicals that already existed These chemicals included water, clay, minerals, etc. The energy present causes these chemicals to react, forming the complex molecules that made life possible

These molecules floated in the oceans for millions of years, eventually joining together to form larger molecules They joined together to form cell like structures that eventually became the first true cells These cells were Prokaryotic The first cells were Anaerobic (without oxygen) Organisms that require oxygen could not survive in Earth’s early atmosphere Because there was not O 2 These molecules floated in the oceans for millions of years, eventually joining together to form larger molecules They joined together to form cell like structures that eventually became the first true cells These cells were Prokaryotic The first cells were Anaerobic (without oxygen) Organisms that require oxygen could not survive in Earth’s early atmosphere Because there was not O 2

The Earth’s First Pollution - Oxygen! More than 3 billion years ago, prokaryotic organisms called cyanobacteria appeared They were photosynthetic organisms that release oxygen into the atmosphere As the atmosphere filled with O 2 some of the oxygen molecules recombined to form the Ozone Ozone - a gas that absorbs ultraviolet (UV) light from the Sun Ozone levels were now low enough to allow life to move onto dry land More than 3 billion years ago, prokaryotic organisms called cyanobacteria appeared They were photosynthetic organisms that release oxygen into the atmosphere As the atmosphere filled with O 2 some of the oxygen molecules recombined to form the Ozone Ozone - a gas that absorbs ultraviolet (UV) light from the Sun Ozone levels were now low enough to allow life to move onto dry land

After 2 billion years, more complex life forms appeared on Earth Eukaryotes are much larger than prokaryotes and contain a central nucleus and organelles The first eukaryotic cells formed about 2 billion years ago and is the ancestor of all plants and animals that exist today The first multicellular eukaryotes are called metazoans. After 2 billion years, more complex life forms appeared on Earth Eukaryotes are much larger than prokaryotes and contain a central nucleus and organelles The first eukaryotic cells formed about 2 billion years ago and is the ancestor of all plants and animals that exist today The first multicellular eukaryotes are called metazoans.

The Paleozoic Era The Paleozoic era - began about 540 million years ago and ended about 248 million years ago. Paleozoic means “ancient life” in Greek Fossils from this era include sponges, corals, snails, clams, squids, etc. Fishes, the earliest animals with backbones, also appeared during this era Ancient sharks became abundant The Paleozoic era - began about 540 million years ago and ended about 248 million years ago. Paleozoic means “ancient life” in Greek Fossils from this era include sponges, corals, snails, clams, squids, etc. Fishes, the earliest animals with backbones, also appeared during this era Ancient sharks became abundant

The Greening of the Earth During the Paleozoic era plants, fungi, and air breathing organisms colonized the dry land This occurred over a 30 million year period Plants provided the first land animals with food and shelter. By the end of this era giant ferns, club mosses, horsetails, and confers covered much of the Earth All major plant groups, except for flowering plants, appeared during this era During the Paleozoic era plants, fungi, and air breathing organisms colonized the dry land This occurred over a 30 million year period Plants provided the first land animals with food and shelter. By the end of this era giant ferns, club mosses, horsetails, and confers covered much of the Earth All major plant groups, except for flowering plants, appeared during this era

Creepers Crawl onto Land Fossils indicated that crawling insects were some of the first animals to appear on land They were followed by salamander-like animals Near the end of this era, reptiles, winged insects, cockroaches, and dragonflies The largest mass extinction known occurred at the end of the Paleozoic era 90% of all marine species died out Fossils indicated that crawling insects were some of the first animals to appear on land They were followed by salamander-like animals Near the end of this era, reptiles, winged insects, cockroaches, and dragonflies The largest mass extinction known occurred at the end of the Paleozoic era 90% of all marine species died out

The Mesozoic Era Mesozoic era - began about 248 million years ago and lasted about 183 million years Mesozoic “middle” in Greek Scientists believe that because of the mass extinctions in the Paleozoic era, a burst of evolution occurred among the remaining organisms (i.e. reptiles) The Mesozoic era is considered the “Age of the Reptiles Mesozoic era - began about 248 million years ago and lasted about 183 million years Mesozoic “middle” in Greek Scientists believe that because of the mass extinctions in the Paleozoic era, a burst of evolution occurred among the remaining organisms (i.e. reptiles) The Mesozoic era is considered the “Age of the Reptiles

Life in the Mesozoic Era Dinosaurs are the most well known reptiles that evolved during this era Dinosaurs dominated the Earth for about 150 million years Dinosaurs had a large variety of physical features and structures i.e. duck bills, spines, plates, etc. Besides dinosaurs, there were marine lizards, the first birds appeared, and flowering plants appeared Dinosaurs are the most well known reptiles that evolved during this era Dinosaurs dominated the Earth for about 150 million years Dinosaurs had a large variety of physical features and structures i.e. duck bills, spines, plates, etc. Besides dinosaurs, there were marine lizards, the first birds appeared, and flowering plants appeared

A Bad Time for Dinosaurs At the end of the Mesozoic era, about 65 million years ago, dinosaurs and many other animal and plant species became extinct One theory suggests, that a large meteorite hit the planet “changing the climate drastically” D.U. At the end of the Mesozoic era, about 65 million years ago, dinosaurs and many other animal and plant species became extinct One theory suggests, that a large meteorite hit the planet “changing the climate drastically” D.U.

The Cenozoic Era The Cenozoic era began about 65 million years ago Cenozoic means “recent life” in Greek Scientists have more information about this era than any previous one Because of the fossils that have been found During this era many kinds of mammals, birds, insects, and flowering plants appeared The Cenozoic era began about 65 million years ago Cenozoic means “recent life” in Greek Scientists have more information about this era than any previous one Because of the fossils that have been found During this era many kinds of mammals, birds, insects, and flowering plants appeared

A Good Time for Large Mammals The Cenozoic era is referred to as the “Age of Mammals” Mammals came to dominate this era Early mammals were forest dwellers and large mammals soon appeared Cenozoic mammals included mastodons, saber-toothed cats, camels, giant ground sloths, and small horses The Cenozoic era is referred to as the “Age of Mammals” Mammals came to dominate this era Early mammals were forest dwellers and large mammals soon appeared Cenozoic mammals included mastodons, saber-toothed cats, camels, giant ground sloths, and small horses

Pop Quiz!!! (please take out a half a piece of paper) 1. What is the main difference between the atmosphere 3.5 billion years ago vs. today's? 2. How do prokaryotic cells differ from eukaryotic cells? 3. Explain why cynobacteria are so important to the development of new life-forms? 4. Match the organisms to the time period in which they first appeared 1. Eukaryotesa. precambrian time 2. Dinosauresb. Paleozoic era 3. Fishesc. Mesozoic era 4. Flowering plantsd. Cenozoic era 5. What is the “family” that humans belong to? 1. What is the main difference between the atmosphere 3.5 billion years ago vs. today's? 2. How do prokaryotic cells differ from eukaryotic cells? 3. Explain why cynobacteria are so important to the development of new life-forms? 4. Match the organisms to the time period in which they first appeared 1. Eukaryotesa. precambrian time 2. Dinosauresb. Paleozoic era 3. Fishesc. Mesozoic era 4. Flowering plantsd. Cenozoic era 5. What is the “family” that humans belong to?

Answers 1. No oxygen vs. enough oxygen for life to exist 2. Eukaryotic cells contain a nucleus, are much bigger, and more complex 3. Cynobacteria were the first organisms to produce atmospheric oxygen 4. 1-a, 2-c,3-b,4-c 5. hominids 1. No oxygen vs. enough oxygen for life to exist 2. Eukaryotic cells contain a nucleus, are much bigger, and more complex 3. Cynobacteria were the first organisms to produce atmospheric oxygen 4. 1-a, 2-c,3-b,4-c 5. hominids

Section 3: Human Evolution Over the years many “human like” fossils have been found i.e Cro-magnon After studying fossil remains, scientists believe that humans have evolved over millions of years How did we get from distant ancestor to today’s modern human? Over the years many “human like” fossils have been found i.e Cro-magnon After studying fossil remains, scientists believe that humans have evolved over millions of years How did we get from distant ancestor to today’s modern human?

Primates Primates - a group of mammals that include humans, apes, monkeys, and prosimians. Characteristics include: 1. Five flexible fingers or four plus an opposable thumb The opposable thumb enables many primates to grip objects 2. Both eyes are located at the front of the head This provides binocular, three dimensional vision Based on physical and genetic similarities, the closest living relative to humans is chimpanzee This conclusion does not mean that humans descended from chimpanzees Hominids - the “family” where humans are placed Refers to humans and “human-like” ancestors The main characteristic that separates hominids from primates, is the ability to walk upright (bipedal) Primates - a group of mammals that include humans, apes, monkeys, and prosimians. Characteristics include: 1. Five flexible fingers or four plus an opposable thumb The opposable thumb enables many primates to grip objects 2. Both eyes are located at the front of the head This provides binocular, three dimensional vision Based on physical and genetic similarities, the closest living relative to humans is chimpanzee This conclusion does not mean that humans descended from chimpanzees Hominids - the “family” where humans are placed Refers to humans and “human-like” ancestors The main characteristic that separates hominids from primates, is the ability to walk upright (bipedal)

Hominid Evolution The first primates were the prosimians (before monkeys) Only a few species survive today (i.e. lemurs and lorises) Paleontologists believe that hominid evolution began in Africa Australopithecines (southern man ape) - among the oldest hominid fossils found Fossils indicate that Australopithecines differed from apes in several ways: The first primates were the prosimians (before monkeys) Only a few species survive today (i.e. lemurs and lorises) Paleontologists believe that hominid evolution began in Africa Australopithecines (southern man ape) - among the oldest hominid fossils found Fossils indicate that Australopithecines differed from apes in several ways:

1) They were bipedal 2) Their brains were larger, though they were smaller than ours 3) Upright posture evolved before large brain development (pg. 217 see Lucy) Hominids with more human-like facial features appeared about 2.3 million years ago This species is known as Homo habilis This species was later replaced by the larger brained - Homo erectus This species had a thick skull, large brow ridge, a low forehead, and a very small chin Homo erectus lived in caves, built fires, and wore clothing 1) They were bipedal 2) Their brains were larger, though they were smaller than ours 3) Upright posture evolved before large brain development (pg. 217 see Lucy) Hominids with more human-like facial features appeared about 2.3 million years ago This species is known as Homo habilis This species was later replaced by the larger brained - Homo erectus This species had a thick skull, large brow ridge, a low forehead, and a very small chin Homo erectus lived in caves, built fires, and wore clothing

Homo erectus marks the beginning of the expansion of human populations across the globe They survived for more than 1 million years, which is longer than any other species has lived They disappeared about 200,000 years ago, which is about the same time that Homo sapiens appeared Homo erectus marks the beginning of the expansion of human populations across the globe They survived for more than 1 million years, which is longer than any other species has lived They disappeared about 200,000 years ago, which is about the same time that Homo sapiens appeared

Neanderthals Neanderthals - lived in Europe and Western Asia beginning about 230,000 years ago They were short and sturdy, had heavy brow regions and their brains were larger than present day humans They hunted large animals, made fires, and wore clothing Neanderthals disappeared about 30,000 years ago Neanderthals - lived in Europe and Western Asia beginning about 230,000 years ago They were short and sturdy, had heavy brow regions and their brains were larger than present day humans They hunted large animals, made fires, and wore clothing Neanderthals disappeared about 30,000 years ago

Cro-Magnons Cro-Magnons - part of the species Homo sapiens Lived in Africa about 100,000 years ago and migrated away about 40,000 years ago They had a small and flatter face and their skull was more rounded (like present day humans) The only major physical difference between Cro- Magnons and present day humans is that Cro- Magnons had a thicker heavier bones They were the first modern humans Cro-Magnons - part of the species Homo sapiens Lived in Africa about 100,000 years ago and migrated away about 40,000 years ago They had a small and flatter face and their skull was more rounded (like present day humans) The only major physical difference between Cro- Magnons and present day humans is that Cro- Magnons had a thicker heavier bones They were the first modern humans

Please Take Out a 1/2 Sheet of Paper 1. Identify three characteristics of primates 2. Compare Homo Habilis with Homo erectus. What made them different from one another. 3. What evidence suggests Neanderthals were like present day humans? 4. T/F Neanderthals had larger brains than present day humans. Bonus What is the difference between a mold fossil and a cast fossil 1. Identify three characteristics of primates 2. Compare Homo Habilis with Homo erectus. What made them different from one another. 3. What evidence suggests Neanderthals were like present day humans? 4. T/F Neanderthals had larger brains than present day humans. Bonus What is the difference between a mold fossil and a cast fossil

Answers 1. Binocular vision, opposable thumbs, mammals 2. H.E. were larger, had a larger brain, and were hunters 3. They lived in social groups, buried their dead, hunted large animals and wore clothing *4 True *5 Mold were imprints that filled with material. Cast were “organisms” that were completely Surrounded by material