Journal #4 – Geologic Time
1. What types of information is included on
the geologic time scale?
2. What is the difference between an Era and
an Epoch?
3. According to the geologic time scale, how
has life on Earth changed since the
beginning of time?
Objective: Understanding the events of
Earth’s past and how they are organized
into a chart.
Geologic Time
 Organic Evolution
 The change in life-forms through time
 Species
 A group of organisms that normally
reproduce only with themselves
Species
 2 Different Species Breed
 Offspring unable to reproduce
Adaptation
 Adaptation
 The ability to change to survive
 Ex. Light colored peppered moths
camouflaged on light tree bark; pollution
causes them to change to darker colors to
survive
 Ex. Galapagos finches and their beaks
Natural Selection
 Natural Selection
 Organisms with traits that are suited to a
certain environment have a better chance
of surviving and reproducing
 1836 by Charles Darwin
Evolution
 Main Causes of Evolution
 Changes to the environment

Caused by plate tectonics
 Competition with others for resources
Endangered vs. Extinct
 Endangered
 When only a small number of members
are living
 Extinct
 When none of its members are living
Extinction
 Human Contribution to Extinction
 Destruction of habitats
 Competition for same food supply
 Overhunting
Geologic Time
 Geologic Time Scale
 A record of Earth’s history that shows
events of life, earth processes, time units
and ages
 Divided into smaller units based on


Types of life-forms living at that time
Geologic events occurring at that time
Geologic Time
Eras
• Largest
• Based on lifeforms and fossil
evidence
Periods
• Divide Eras
• Based on lifeforms and
geologic events
Epochs
• Smallest
• Divide Periods
Geologic Time
 Precambrian
 Longest geologic time unit in Earth’s
history
 Began: 4600 million years ago (4.6 billion
years)
 Ended: 540 million years ago
Precambrian
 Precambrian Fossils
 Limited




Rocks deeply buried or eroded
Rocks have been changed by heat and pressure
Early organisms were soft-bodied
Early organisms were small and single-celled
Cyanobacteria
 Cyanobacteria
 Bacteria and algae combine and
photosynthesize to form stromatolites
 Appeared: 3.5 billion years ago
 Take in CO2, Release O2
Cyanobacteria
 Cyanobacteria
 Importance: changed Earth’s atmosphere
by adding free oxygen to the air

Formed the ozone layer protecting organisms
from UV light
 Single-celled organisms evolved into
complex organisms
Invertebrate
 Invertebrate
 Animal without a backbone
 Appeared: end of the Precambrian
 Ex. Jellyfish, sponges, worms
Paleozoic Era
 Paleozoic Era
 “Ancient Life”
 Beginning marked by the development of
hard parts
 Began: 540 million years ago
 Ended: 245 million years ago
Paleozoic Era
 Paleozoic Era
 Abundant Life: ocean dwelling marine
organisms



Caused by warm, shallow seas covering most
of earth
Appeared: Cambrian Period
Ex. Trilobites, brachiopods, cephalopods,
crinoids
Paleozoic Era Animals
 Vertebrate
 Animals with a backbone
 Appeared: Ordovician Period
 Ex. Jawless fish, bony fishes, reptiles,
mammals
Paleozoic Era Animals
 Amphibian
 Vertebrates that live on land by must
return to water to reproduce (lay eggs)
 Appeared: Devonian Period
 Ex. Frogs, salamanders
Paleozoic Era Animals
 Reptiles
 Vertebrates that live entirely on land; eggs
have leathery or mineralized covering
 Appeared: Late Carboniferous
(Pennsylvanian Period)
 Ex. Tortoises, snakes, lizards, crocodiles
Paleozoic Era Plants
 Ferns, Palms, Ginkgos, Pines
 Appeared: Devonian Period
Paleozoic Era Plants
 Gymnosperms
 “naked seed plant”; no fruit covering their
seeds
 Appeared: Carboniferous Period
 Ex. Eastern White Pine
Paleozoic Era
 Appalachian Mountains
 Formed at the end of the Paleozoic
 What marked the end of the Paleozoic?
 Largest mass extinction in Earth’s history
 Formation of Pangaea
Mesozoic Era
 Mesozoic Era
 “Middle Life”
 “Age of the Dinosaurs”
 Began: 245 million years ago
 Ended: 66 million years ago
Mesozoic Era
Pangaea
All Continents
Laurasia
North America,
Europe, Asia,
Greenland
Gondwanaland
South America,
Africa, Antarctica,
India, Australia
Mesozoic Era Animals
 Small Dinosaurs
 Appeared: Triassic Period
 Evidence of being Warm-Blooded



Tracks (trace fossils) indicate fast motion
Traveled in herds and nurtured young
Bone structure resembles other warm-blooded
animals
Mesozoic Era Animals
 Mammals
 Appeared: Triassic Period
 Traits Allowing Survival



Hair or Fur
Warm Blooded
Produce Milk to Feed Young
Mesozoic Era Animals
 Birds
 Appeared: Jurassic Period

Ex. Archaeopteryx had wings and feathers like
a bird, teeth, claws and tail like a dinosaur
Mesozoic Era Plants
 Angiosperms
 Flowering plants
 Produce seeds with a hard outer covering
and/or fruit
 Appeared: Early Cretaceous Period
 Ex. Fruits, vegetables, flowers, flowering
trees
Mesozoic Era
 What marked the end of the Mesozoic Era?
 Break up of Pangaea
 Seas drained from lands
 Extensive volcanism
 Extinction of the dinosaurs
Cenozoic Era
 Cenozoic Era
 “Recent Life”
 Age of the Mammals
 Begin: 66 million years ago
 Current Time
Cenozoic Era
 Alps in Europe
 Form from the collision between African
and Eurasian Plates
Cenozoic Era
 The Himalaya Mountains
 Formed from the collision between the
Indian and Eurasian Plates
Cenozoic Era Animals
 Placental Mammals
 Nourish their young internally from a
placenta
 Offspring born live and independent
 First Appeared: Cretaceous Period
 Ex. Rodents, bats, dogs, cats, cows,
humans
Cenozoic Era Animals
 Marsupials
 Offspring are born immature
 Must complete development in a pouch
 First Appeared: Cretaceous Period
 Ex. Kangaroo, koala, wombat, opossum
 Australia has the greats population of
marsupials
Cenozoic Era Animals
 Monotremes
 Egg-laying mammals
 Ex. Platypus
Homo Sapiens
Homo Sapiens
500,000 years ago
Homo Sapiens
Homo Sapiens
Neanderthalensis
Sapiens
250,000 years ago
100,000 years ago
Humans
 Humans
 Dominant life form for the past 10,000
years

Started agriculture, domestication of animals,
cities, writing