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Time Scale 2 - The Earliest Animal Life
Events - < 11
The first multicellular fossils:
600 million yrs ago
12
The Cambrian explosion:
543 million years ago
13
The first vertebrates:
530 million years ago
14
Spread of vertebrates (fish):
525 million years ago
15
The first amphibians:
360 million years ago
16
The first reptiles:
315 million years ago
17
The Permian extinction:
250 million years ago
18
The first mammals & dinosaurs:
220-200 million years ago
19
The earliest birds:
145 million years ago
20
The first flowering plants:
125 million years ago
>

Event 18

“GOT MILK?”
EARLY MAMMALS AND DINOSAURS
220-200 million years ago

Thrinaxodon and pups
A mammal-like reptile, Thrinaxodon, and her pups. This carnivore lived about 245 million years ago during the Triassic. It combines apparent mammalian traits such as a fur coat and likely warm-bloodedness along with reptilian traits such as egg-laying and various features of its skeleton.
Credit: Illustration by John Sibbick, Courtesy of John Sibbick Illustration. This image is used with permission. All rights reserved.

Most people don’t realize it, but the class of animals that we belong to, the mammals, evolved from mammal-like reptiles at the same time as the emergence of early dinosaurs, around 200 million years ago. Mammals and dinosaurs therefore co-existed for some 135 million years before dinosaurs went extinct. Although small and insignificant at first (and probably nocturnal, or moving and feeding at night), they would later become a major player in the History of Life. These early mammals established the foundation of what would become the human condition.

Today’s mammals, as contrasted to reptiles, are characterized by being warm-blooded (being able to maintain a constant body temperature, making them more active in cooler weather), bearing their young live rather than laying eggs, nourishing their young by producing milk (with mammary glands, thus their name), having larger brains, having hair on their bodies, and having sweat glands in the skin, and each side of the lower jaw (mandible) composed of only one bone rather than several. Most mammals also show more parental care for their young than reptiles do.

Ceratosaurs and Apatosaurus
Early dinosaurs co-evolved with the early mammals. This shows the carnivorous dinosaur Ceratosaurus in the foreground eyeing a herd of Apatosaurus dinosaurs (formerly known as Brontosaurus) around 150 million years ago.
Credit: Illustration by John Sibbick, courtesy of John Sibbick Illustration. This illustration is used with permission. All rights reserved.

One important early fossil mammal form, Megazostrodon, has been found in southern Africa around 200 million years ago (Late Triassic). It was similar in size and form to modern shrews (about 4 inches in length), probably hunted insects and very small reptiles, and chewed them up with teeth that showed another hallmark of mammals: differentiated teeth for different functions. These teeth were the incisors, canines, premolars, and molars or cheek teeth; this basic pattern is still retained in our own species today. These early mammals also had a first set of deciduous teeth (“milk teeth”) that were shed as the animal grew, to be replaced by the permanent adult dentition. These early mammals were probably still egg-laying (like the modern primitive mammals, the platypus and the spiny anteater of Australia) and not yet milk-producing, but nonetheless show many of the anatomical features in their skeletons, especially in their skulls, that denote their mammalian status.



HOW DO WE KNOW?

The fossil record shows a detailed transition from reptiles to mammal-like reptiles to mammals between 300 million and 100 million years ago.

WHY SHOULD I CARE?

Although the early mammals were a relatively insignificant class of animals during the Age of Reptiles, they would ultimately come to inherit the earth with the extinction of the dinosaurs. The early mammals’ small size, warm-bloodedness, and ability to live underground probably sustained them through the catastrophic times that were to come. Mammals were able to diversify into an astonishing range of forms adapted to the ground, to the trees (like our early mammalian ancestors), to the air, to the rivers, lakes, and seas, and to tunneling in the earth. The anatomical pattern (e.g. differentiated teeth) and physiological pattern (warm-bloodedness, milk-producing) of these early mammals would be the foundations of the human condition. This foundation was established by about 200 million years ago.

Today there are 19 orders of mammals (including ours, the Primates) comprising some 4,000 living species around the world. All of these lines can be traced back to the earliest mammals.

 

 


 

WEB RESOURCES

 

This is a YouTube video, "Highway of Life: The Ancestors of All Mammals."
http://www.youtube.com/watch?v=oK7o8k25qPA

An easy to understand survey of the evolution of mammals.
http://www.earthlife.net/mammals/evolution.html


This is a basic information site on the differences between reptiles and mammals.
http://genesispanthesis.tripod.com/fossils/rept_mam.html

 

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1

"From Nothing to Everything:
The Origins of the Universe,
the Solar System, Earth, and Life"
13.7 billion to 1 billion years ago

.

"From Nothing to Everything:
The Origins of the Universe, the Solar System, Earth, and Life"
13.7 billion to 1 billion years ago

View Time Scale >>

1

"The Big Bang"
The Origins of Matter, Energy, Space, and Time
13.7 billion years ago

"The Big Bang"
The Origins of Matter, Energy, Space, and Time
13.7 billion years ago

View Event >>

2

"Great Balls of Fire"
The First Stars
13.5 billion years ago

"Great Balls of Fire"
The First Stars
13.5 billion years ago

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3

"Cosmic Alchemy"
The Creation of the Heavier Elements
13.4 billion years ago

"Cosmic Alchemy"
The Creation of the Heavier Elements
13.4 billion years ago

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4

"Spinning Wheels"
The First Galaxies
13 billion years ago

"Spinning Wheels"
The First Galaxies
13 billion years ago

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5

"Here Comes the Sun"
The Birth of the Solar System, Including the Earth
4.6 billion years ago

"Here Comes the Sun"
The Birth of the Solar System, Including the Earth
4.6 billion years ago

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6

"Earth, Wind and Fire"
The First Rocks, Oceans and Atmosphere
4.5 billion years ago

"Earth, Wind and Fire"
The First Rocks, Oceans and Atmosphere
4.5 billion years ago

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7

"Just Add Water"
The Origins of Life
3.8 billion years ago

"Just Add Water"
The Origins of Life
3.8 billion years ago

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8

"The Great Rust"
The Addition of Oxygen to the Atmosphere and Oceans
3 billion years ago

"The Great Rust"
The Addition of Oxygen to the Atmosphere and Oceans
3 billion years ago

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9

"Snowball Earth"
The First Ice Ages
2.2 billion years ago

"Snowball Earth"
The First Ice Ages
2.2 billion years ago

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10

"Kingdom of Beasts"
The Rise of Animals
1 billion years ago

"Kingdom of Beasts"
The Rise of Animals
1 billion years ago

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2

"All Creatures Great and Small:
The Cambrian Explosion of
Animal Life and its Aftershocks"
1 billion to 100 million years ago

.

"Animal House:
The Cambrian Explosion of Animal Life and its Aftershocks"
1 billion to 100 million years ago

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11

"Movers and Shakers"
The First Definite Multicellular Animals
600 million years ago

"Movers and Shakers"
The First Definite Multicellular Animals
600 million years ago

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12

"AnimalHouse"
The Cambrian Explosion
543 million years ago

"AnimalHouse"
The Cambrian Explosion
543 million years ago

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13

"In Search of the Lost Chordate"
Finding the Ancestor of Vertebrates (and Ourselves)
530 million years ago

"In Search of the Lost Chordate"
Finding the Ancestor of Vertebrates (and Ourselves)
530 million years ago

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14

"Get a Backbone"
The Rise of the Vertebrates
525 million years ago

"Get a Backbone"
The Rise of the Vertebrates
525 million years ago

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15

"Get out of the Pool"
Early Amphibians
360 million years ago

"Get out of the Pool"
Early Amphibians
360 million years ago

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16

"Landlubbers"
The First Reptiles
315 million years ago

"Landlubbers"
The First Reptiles
315 million years ago

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17

"The Great Dying"
The Permian Extinction
250 million years ago

"The Great Dying"
The Permian Extinction
250 million years ago

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18

"Got Milk?"
Early Mammals and Dinosaurs
220 - 200 million years ago

"Got Milk?"
Early Mammals and Dinosaurs
220 - 200 million years ago

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19

"Up, Up, and Away"
The Earliest Birds
145 million years ago

"Up, Up, and Away"
The Earliest Birds
145 million years ago

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20

"Flower Power"
The First Flowering Plants
125 million years ago

"Flower Power"
The First Flowering Plants
125 million years ago

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3

"The Meek Inheritors: the Dinosaur Extinction
and the Rise of Mammals"
100 million to 10 million years ago

.

"The Meek Inheritors: the Dinosaur Extinction and the Rise of Mammals"
100 million to 10 million years ago

View Time Scale >>

21

"Cretaceous Park"
The Later Dinosaurs
95-65 million years ago

"Cretaceous Park"
The Later Dinosaurs
95-65 million years ago

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22

"One Extraterrestial Impact Can Ruin your Whole Day":
The Dinosaur Extinction
65 million years ago

"One Extraterrestial Impact Can Ruin your Whole Day":
The Dinosaur Extinction
65 million years ago

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23

"A Warm and Fuzzy Feeling"
The Mammalian Radiation
60 million years ago

"A Warm and Fuzzy Feeling"
The Mammalian Radiation
60 million years ago

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24

"Orogenous Zone"
The Rise of the Himalayas
55 million years ago

"Orogenous Zone"
The Rise of the Himalayas
55 million years ago

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25

"Of the First Order"
The Radiation of the Primates
55 million years ago

"Of the First Order"
The Radiation of the Primates
55 million years ago

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26

"The Land Down Under"
The Origin of Australia and its Animals
40 million years ago

"The Land Down Under"
The Origin of Australia and its Animals
40 million years ago

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27

"Hey, Hey, We're the Monkeys"
The Rise of Monkeys
35 million years ago

"Hey, Hey, We're the Monkeys"
The Rise of Monkeys
35 million years ago

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28

"Grazing in the Grass"
The Spread of Grasslands and Grazing Animals
Beginning 25 million years ago

"Grazing in the Grass"
The Spread of Grasslands and Grazing Animals
Beginning 25 million years ago

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29

"The Sultans of Swing"
The Rise of Apes
23 million years ago

"The Sultans of Swing"
The Rise of Apes
23 million years ago

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30

"Father of Kong"
The Earliest Gorilla-like Forms
10 million years ago

"Father of Kong"
The Earliest Gorilla-like Forms
10 million years ago

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4

"Upstanding Apes:
The Rise of Hominids,
the Role of Rock,
and Food for Thought"
10 million to 1 million years ago

.

"Upstanding Apes:
The Rise of Hominids, the Role of Rock, and Food for Thought"
10 million to 1 million years ago

View Time Scale >>

31

"Branching Out"
The Last Shared Ancestor of Apes and Humans
7 million years ago

"Branching Out"
The Last Shared Ancestor of Apes and Humans
7 million years ago

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32

"Upstanding Apes"
The Earliest Bipedal Hominins
6 to 4 million years ago

"Upstanding Apes"
The Earliest Bipedal Hominins
6 to 4 million years ago

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33

"I am an Ape-Man"
The Earlier Australopithecine
4.0-2.5 million years ago

"I am an Ape-Man"
The Earlier Australopithecine
4.0-2.5 million years ago

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34

"The Big Chill"
The Beginning of Climatic Cooling
3 to 2 million years ago

"The Big Chill"
The Beginning of Climatic Cooling
3 to 2 million years ago

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35

"Our Poor Cousins"
The Later Australopithecine and their Extinction
2.6-1.0 million yeas ago

"Our Poor Cousins"
The Later Australopithecine and their Extinction
2.6-1.0 million yeas ago

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36

"The Role of Rock"
The Earliest Stone Tools
2.6 million years ago

"The Role of Rock"
The Earliest Stone Tools
2.6 million years ago

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37

"I'm Your Handy Man"
The Emergence of the Genus Homo and Brain Expansion
1.9-1.5 million years ago

"I'm Your Handy Man"
The Emergence of the Genus Homo and Brain Expansion
1.9-1.5 million years ago

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38

"Bigger and Badder"
The Emergence of Homo Erectus
1.8 million years ago

"Bigger and Badder"
The Emergence of Homo Erectus
1.8 million years ago

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39

"Out of Africa"
The Earliest Eurasians
1.8 million years ago

"Out of Africa"
The Earliest Eurasians
1.8 million years ago

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40

"Axes of Power"
The Invention of the Handaxe
1.76 million years ago

"Axes of Power"
The Invention of the Handaxe
1.76 million years ago

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5

"Becoming Human (or Just About):
The Rise of Homo Sapiens
and Our Neanderthal Cousins"
1 million to 100,000 years ago

.

"Becoming Human (or Just About):
The Rise of Homo Sapiens and Our Neanderthal Cousins"
1 million to 100,000 years ago

View Time Scale >>

41

"Big Brains, Big Faces"
Homo heidelbergensis and Probably Language
500,000 to 250,000 years ago

"Big Brains, Big Faces"
Homo heidelbergensis and Probably Language
500,000 to 250,000 years ago

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42

"Fearful Symmetry"
Later Refined Handaxes
500,000 to 250,000 years ago

"Fearful Symmetry"
Later Refined Handaxes
500,000 to 250,000 years ago

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43

"Bring Out Your Dead"
The Origins of Ritual Behavior
400,000 years ago

"Bring Out Your Dead"
The Origins of Ritual Behavior
400,000 years ago

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44

"Get the Point?"
The First Spears
400,000 years ago

"Get the Point?"
The First Spears
400,000 years ago

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45

"Chips Off the Old Block"
Prepared Core Technologies
300,000 years ago

"Chips Off the Old Block"
Prepared Core Technologies
300,000 years ago

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46

"Light My Fire"
The Controlled Use of Fire
300,000 years ago

"Light My Fire"
The Controlled Use of Fire
300,000 years ago

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47

"Almost Human"
Neandertals and Nearly Modern Humans
Beginning 250,000 years ago

"Almost Human"
Neandertals and Nearly Modern Humans
Beginning 250,000 years ago

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48

"Welcome to Middle Earth"
The Middle Palaeolithic
Beginning 250,000 years ago

"Welcome to Middle Earth"
The Middle Palaeolithic
Beginning 250,000 years ago

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49

"Seashells by the Seashore"
Intensive Exploitation of Seafoods
165,000 years ago

"Seashells by the Seashore"
Intensive Exploitation of Seafoods
165,000 years ago

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50

"A Modern Stone Age Family"
The Emergence of Homo Sapiens
160,000 years ago

"A Modern Stone Age Family"
The Emergence of Homo Sapiens
160,000 years ago

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6

"The Creative Explosion:
The Rise of Symbolism, Language,
Religion, Art, and Music"
100,000 to 10,000 years ago

.

"The Creative Explosion:
The Rise of Symbolism, Language, Religion, Art, and Music"
100,000 to 10,000 years ago

View Time Scale >>

51

"Points of Conflict"
The Earliest Compound Tools & Points
100,000 years ago

"Points of Conflict"
The Earliest Compound Tools & Points
100,000 years ago

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52

"Rest in Peace"
The First Burials
90,000 years ago

"Rest in Peace"
The First Burials
90,000 years ago

View Event >>

53

"Bling-Bling"
The First Personal Decoration
80,000 years ago

"Bling-Bling"
The First Personal Decoration
80,000 years ago

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54

"A Roof Over Your Head"
The First Architecture
42,000 years ago

"A Roof Over Your Head"
The First Architecture
42,000 years ago

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55

"Blade Runners"
Upper Palaeolithic Blade Technologies
40,000 years ago

"Blade Runners"
Upper Palaeolithic Blade Technologies
40,000 years ago

View Event >>

56

"Brave New Worlds"
The Peopling of Australia and the Americas
40,000 to 12,000 years ago

"Brave New Worlds"
The Peopling of Australia and the Americas
40,000 to 12,000 years ago

View Event >>

57

"Express Yourself"
The First Representational Art & Music
35,000 years ago

"Express Yourself"
The First Representational Art & Music
35,000 years ago

View Event >>

58

"A Stitch in Time"
The First Needles and Sewing
25,000 years ago

"A Stitch in Time"
The First Needles and Sewing
25,000 years ago

View Event >>

59

"Bend Me, Shape Me"
The First Pottery
16,000 years ago

"Bend Me, Shape Me"
The First Pottery
16,000 years ago

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60

"Draw Back Your Bow"
The First Bow and Arrow
11,000 years ago

"Draw Back Your Bow"
The First Bow and Arrow
11,000 years ago

View Event >>

7

"From Farm to the City:
The Neolithic and Urban Revolutions
and their Consequences"
10,000 to 1,000 years ago

.

"From Farm to the City:
The Neolithic and Urban Revolutions and their Consequences"
10,000 to 1,000 years ago

View Time Scale >>

61

"Row, Row, Row Your Boat"
The First Boats
10,000 years ago

"Row, Row, Row Your Boat"
The First Boats
10,000 years ago

View Event >>

62

"Down on the Farm"
The Neolithic Revolution
10,000 years ago

"Down on the Farm"
The Neolithic Revolution
10,000 years ago

View Event >>

63

"Heavy Metal"
The Origins of Metallurgy
8,000 years ago

"Heavy Metal"
The Origins of Metallurgy
8,000 years ago

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64

"Easy Riders"
The Development of Ships and Mounted Horse Transportation
6,000 to 5,000 years ago

"Easy Riders"
The Development of Ships and Mounted Horse Transportation
6,000 to 5,000 years ago

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65

"We Built This City"
Cities and Complex Societies
5,500 years ago

"We Built This City"
Cities and Complex Societies
5,500 years ago

View Event >>

66

"Write This Down"
The Origins of Writing and Notation
5,000 years ago

"Write This Down"
The Origins of Writing and Notation
5,000 years ago

View Event >>

67

"Big Wheels Keep on Turnin"
Wheeled Vehicles
5,000 years ago

"Big Wheels Keep on Turnin"
Wheeled Vehicles
5,000 years ago

View Event >>

68

"Iron Man"
The Iron Age
3,500 years ago (1500 BC)

"Iron Man"
The Iron Age
3,500 years ago (1500 BC)

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69

"Power to the People"
The First Democracy
2,560 years ago (550 BC)

"Power to the People"
The First Democracy
2,560 years ago (550 BC)

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70

"What's Your Plan?"
Large-scale Urban Planning
2,210 years ago (200 B.C.)

"What's Your Plan?"
Large-scale Urban Planning
2,210 years ago (200 B.C.)

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8

"Ages of Enlightenment:
From the Dark Ages of Superstition
to the Scientific Revolution"
1,000 to 100 years ago

.

"Ages of Enlightenment:
From the Dark Ages of Superstition to the Scientific Revolution"
1,000 to 100 years ago

View Time Scale >>

71

"Fire and Brimstone"
The Rise of Firearms
Beginning 1300 AD

"Fire and Brimstone"
The Rise of Firearms
Beginning 1300 AD

View Event >>

72

"A Reawakening"
The Renaissance in the Western World
Beginning 1400 AD

"A Reawakening"
The Renaissance in the Western World
Beginning 1400 AD

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73

"Land Ho!"
Age of Exploration & Exploitation
Beginning 1400 AD

"Land Ho!"
Age of Exploration & Exploitation
Beginning 1400 AD

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74

"Hot off the Presses"
The Printing Press and Movable Type
Beginning 1455 AD

"Hot off the Presses"
The Printing Press and Movable Type
Beginning 1455 AD

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75

"From Superstition to Science"
The Scientific Revolution
Beginning 1543 AD

"From Superstition to Science"
The Scientific Revolution
Beginning 1543 AD

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76

"All Fired Up"
The Industrial Revolution
Beginning 1760 AD

"All Fired Up"
The Industrial Revolution
Beginning 1760 AD

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77

"Start Me Up"
Powered Modern Transport
Beginning 1802 AD

"Start Me Up"
Powered Modern Transport
Beginning 1802 AD

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78

"You Oughta Be in Pictures"
Photography and Cinematography
Beginning 1826 AD

"You Oughta Be in Pictures"
Photography and Cinematography
Beginning 1826 AD

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79

"From a Distance"
Long-Distance Communications
Beginning 1830 AD

"From a Distance"
Long-Distance Communications
Beginning 1830 AD

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80

"Bright Lights, Big City"
Electric Light and Power
Beginning 1879 AD

"Bright Lights, Big City"
Electric Light and Power
Beginning 1879 AD

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9

"Modern Times: The Last Century,
Laying the Foundations of
the World We Live In"
100 to 10 years ago

.

"Modern Times: The Last Century, Laying the Foundations of the World We Live In"
100 to 10 years ago

View Time Scale >>

81

"It's All Relative"
Relativity and Quantum Theory
Late 1800s, early 1900s

"It's All Relative"
Relativity and Quantum Theory
Late 1800s, early 1900s

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82

"Rocket Man"
Rockets, Satellites, and Lunar Landings
Beginning 1926 AD

"Rocket Man"
Rockets, Satellites, and Lunar Landings
Beginning 1926 AD

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83

"You're On the Air"
Television
Beginning 1935 AD

"You're On the Air"
Television
Beginning 1935 AD

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84

"Bits and Bytes"
Computers, Transistors, Silicon Chips
Beginning 1937 AD

"Bits and Bytes"
Computers, Transistors, Silicon Chips
Beginning 1937 AD

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85

"When You're a Jet"
Jet Aircraft
1939 AD

"When You're a Jet"
Jet Aircraft
1939 AD

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86

"Miracle Drugs & Medical Devices"
Penicillin and Other Medical Advances
Beginning 1941 AD

"Miracle Drugs & Medical Devices"
Penicillin and Other Medical Advances
Beginning 1941 AD

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87

"The Genie Has Left the Bottle"
Dawn of the Atomic Age
Beginning 1942 AD

"The Genie Has Left the Bottle"
Dawn of the Atomic Age
Beginning 1942 AD

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88

"Cracking the Code"
DNA Structure & Genetic Engineering
Beginning 1953 AD

"Cracking the Code"
DNA Structure & Genetic Engineering
Beginning 1953 AD

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89

"Can You Hear Me Now?"
Advanced Telecommunications
Beginning 1973 AD

"Can You Hear Me Now?"
Advanced Telecommunications
Beginning 1973 AD

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90

"Surf's Up!"
The World Wide Web
Beginning 1989 AD

"Surf's Up!"
The World Wide Web
Beginning 1989 AD

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10

"The Age of Connections:
The Past Decade of Innovations
and Their Implications"
The last 10 years

.

"The Age of Connections:
The Past Decade of Innovations and Their Implications"
The last 10 years

View Time Scale >>

91

"Where the Heck Are We?"
Widespread Use of GPS & Satellite Imaging

"Where the Heck Are We?"
Widespread Use of GPS & Satellite Imaging

View Event >>

92

"Ch-Ch-Ch-Ch-Changes, that Make the Strain..."
Overpopulation & Climate Change

"Ch-Ch-Ch-Ch-Changes, that Make the Strain..."
Overpopulation & Climate Change

View Event >>

93

"Green Machines"
Alternative Energy

"Green Machines"
Alternative Energy

View Event >>

94

"Who Are You?"
The Human Genome Project

"Who Are You?"
The Human Genome Project

View Event >>

95

"Closer Encounters"
Recent Advances in Astronomy

"Closer Encounters"
Recent Advances in Astronomy

View Event >>

96

"Cellmates"
Stem Cell & Related Research

"Cellmates"
Stem Cell & Related Research

View Event >>

97

"Keep Searchin"
Widespread Use of Search Engines

"Keep Searchin"
Widespread Use of Search Engines

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98

"Say Hello to My Little Friends"
The Rise of Nanotechnology

"Say Hello to My Little Friends"
The Rise of Nanotechnology

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99

"Here, There, and Everywhere..."
Instantaneous Communication & World-Wide Connections

"Here, There, and Everywhere..."
Instantaneous Communication & World-Wide Connections

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100

"Living for the Future"
The Idea of Sustainability

"Living for the Future"
The Idea of Sustainability

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