The History of Life on
Earth
MELC
•Describe general features of the
history of life on Earth, including
generally accepted dates and
sequence of the geologic time scale
and characteristics of major groups
of organisms present during these
time periods (STEM_BIO11/12-IIIc-g8).
100-Million-Year-Old Fossil (Ammonite)Found In Bicol
“Mortoniceras is an index ammonite,
meaning its presence would indicate the
age of the rock it is embedded in as about
100 million years old or in the Cretaceous
period,” the Japanese scientist said in
Catanduanes Tribune
Classified among prehistoric animals, the
Nationalgeographic.com said ammonites
first appeared about 240 million years
ago. Ammonites were predatory, squid-like
creatures that lived inside coil-shaped
shells. They were prolific breeders, lived in
schools and are among the most abundant
fossils found today. They went extinct with
the dinosaurs 65 million years ago.
Scientists use the various shapes and
sizes of ammonite shells that appeared
and disappeared through the ages to
date other fossils. The most important
among the species found by the team,
Shigeta said in the Tribune article, is the
Mortoniceras,
Uncovering Clues
How do we learn about ancient life?
• Paleontologists use fossils to reconstruct the
history of life.
• A fossil is a trace or an imprint of a living thing
that is preserved by geological processes.
• Fossils of single-celled organisms date as far back
as 3.8 billion years.
What can we learn from fossils?
• All of the fossils that have been discovered
worldwide make up the fossil record.
• Examining the fossil record helps scientists
identify when different species lived and died.
• There are two ways to describe the ages of fossils.
What can we learn from fossils?
• Relative dating determines whether a fossil
formed before or after another fossil formed.
Newer fossils are found in layers of rock that are
above older fossils.
• Absolute dating estimates the age of a fossil in
years.
• Estimations are based on information from
radioactive elements in certain rocks near the
fossil.
What can we learn from fossils?
• The fossil record gives evidence of many of the
different organisms that have lived during Earth’s
long history.
• Changes in population can be preserved in fossils
over many generations.
• Some species are present in the fossil record for a
short period of time, while others survive for long
time spans without much change.
What can we learn from fossils?
• An extinction happens when every individual of a
species dies.
• A mass extinction occurs when a large number of
species go extinct during a relatively short amount
of time.
• Gradual environmental changes and catastrophic
events, such as the impact of an asteroid, can
cause mass extinctions.
What can we learn from fossils?
• Extinctions and mass extinctions are documented
in the fossil record.
• Fossils that were common in certain rock layers
may decrease in frequency and eventually
disappear altogether.
• Evidence in the fossil record helps scientists form
hypotheses about how and when species went
extinct.
What is the geologic time scale?
• The geologic time scale is the standard method
used to divide Earth’s 4.6-billion-year natural
history into manageable parts.
• Paleontologists adjust and add details to the
geologic time scale when new evidence is found.
• The early history of Earth has been poorly
understood, because fossils from this time span
are rare.
What is the geologic time scale?
• Boundaries between geologic time intervals
correspond to significant changes in Earth’s
history.
• Some major boundaries are defined by mass
extinctions or significant changes in the number of
species.
• Some boundaries are defined by major changes in
Earth’s surface or climate.
• The Geological time scale is a record of
the life forms and geological events in
Earth’s history.
• Scientists developed the time scale by
studying rock layers and fossils world
wide.
• Radioactive dating helped determine the
absolute divisions in the time scale.
Divisions of Geologic Time: Eons
Eons are divided into Eras. Eras are
subdivided into periods...periods are
subdivided into epochs.
Era
Period
Epoch
E + P = EP
FOUR Eras…
• PRE-CAMBRIAN – 88% of earth’s history
• Paleozoic (ancient life)
– 544 million years ago…lasted 300 million yrs
• Mesozoic (middle life)
– 245 million years ago…lasted 180 million yrs
• Cenozoic (recent life)
– 65 million years ago…continues through present day
Divisions of Geologic Time
• Geological time begins with Precambrian
Time. Precambrian time covers
approximately 88% of Earth’s history.
Precambrian
• The earliest living organisms were microscopic
bacteria, which show up in the fossil record as
early as 3.4 billion years ago.
• Some three billion years ago the Earth's
atmosphere was virtually devoid of oxygen.
• It's thought the final stages of Precambrian time
were marked by a prolonged global ice age.
Paleozoic Era (Ancient Life)
• The Cambrian period is the 1st period of the Paleozoic
Era. “Age of the Trilobites”
• Explosion of life in the oceans began during this era.
• Most of the continents were covered in warm, shallow
seas.
– Invertebrates were dominate - Trilobites
– Fish emerged during this time
– Fish led to the arrival of amphibians
• The end of the Paleozoic era is called the “Age of Amphibians”
– Early land plants including mosses, ferns and cone-bearing
plants.
– The early coal forming forests were also formed during this
time.
Paleozoic Era
• Much of the limestone quarried for building and
industrial purposes, as well as the coal deposits
of western Europe and the eastern United
States, were formed during the Paleozoic.
• The Cambrian (beginning) opened with the
breakup of the world-continent Rodinia and
closed with the formation of Pangaea, as the
Earth's continents came together once again.
– This event is thought to have caused the
climate changes that led to mass extinction
event.
• The Appalachian mountains were formed during
this time.
Paleozoic Era
• At the end of the Paleozoic, the largest mass
extinction in history wiped out approximately
90% of all marine animal species and 70% of
land animals.
– Possible causes of this Mass Extinction Event
• Lowering of sea levels when the continents were
rejoined as Pangaea (convergent boundary)
• Increased volcanic activity (ash and dust)
• Climate changes – cooler climate
Trilobites
• Lived in Earth’s ancient seas
• Extinct before the dinosaurs
came into existence
• Cambrian Period is know as
the “Age of the Trilobites”
(put in on table)
Brachiopods
• Marine animals that resemble clams.
Early Fish
Early fish did not have jaws.
Some species of sharks
were in existence at this
time.
Frilled Shark that was found in Japan in January 2007. This shark was
considered a “living fossil”
Early Land Plants
Mosses
Cone bearing plants
Ferns
Mesozoic Era – Middle Life
• At the beginning of this era the continents
were joined as Pangaea.
• Pangaea broke up around the middle of
this era.
• Reptiles became the most abundant
animals because of their ability to adapt to
the drier climate of the Mesozoic Era.
– Skin maintains body fluids
– Embryos live in shells
Mesozoic Era
• Dinosaurs were also very active in this
era.
– First small dinosaurs appeared in the Triassic
Period.
– Larger and more abundant dinosaurs
appeared in the Jurassic Period.
• Small mammals and birds also appeared
during this era.
– The mammals were small, warm-blooded
animals. Hair covering their bodies.
• These characteristics help them survive in
changing environments.
Mesozoic Era
• The main plant life of this time were
Gymnosperms or plants that produce seeds,
but no flowers.
– Pine Trees
• Flowering plants appeared during the END of
this era.
Mesozoic Era
• This era ended with a mass extinction event
about 65 million years ago.
– Many groups of animals, including the dinosaurs
disappeared suddenly at this time.
• Many scientists believe that this event was
caused by a comet or asteroid colliding with the
Earth.
Mesozoic Era – Mass Extinction
Event
• Asteroid or Comet collides with Earth.
–
–
–
–
–
Huge cloud of smoke and dust fills the air
Blocks out sunlight
Plants die
Animals that eat plants die
Animals that eat plant-eaters die.
• However, not all forms of life died during this
event. Many animals that you see today are
descendants from the survivors of this extinction
event.
Dinosaurs
Mesozoic Reptiles
Mesozoic Mammals
Mesozoic Plants
Flowering plants evolved
towards the end of the
Mesozoic Era.
Cenozoic Era – Recent Life
• Began about 65 million years ago and continues
today!!!!!
– Climate was warm and mild.
– Marine animals such as whales and dolphins evolved.
• Mammals began to increase and evolve adaptations
that allowed them to live in many different
environments – land, air and the sea.
– Grasses increased and provided a food source for grazing
animals
• Many mountain ranges formed during the Cenozoic
Era
– Alps in Europe and Himalayas in India; Rocky Mountains in
the USA
Cenozoic Era
• Growth of these mountains may have helped to
cool down the climate
– Ice Ages occurred late in the Cenozoic Era
(Quaternary Period).
• As the climate changed, the animals had to
adapt to the rise and fall of the oceans caused
by melting glaciers.
• This era is sometimes called the “Age of
Mammals”
Cenozoic Era
• Marine animal examples:
– Algae, Mollusks, Fish and Mammals
• Land animal examples:
– Bats, Cats, Dogs, Cattle and Humans
– Humans are thought to have appeared around 3.5
million years ago (during the most recent period –
Quaternary).
• Flowering plants were now the most common
plant life.
Cenozoic Mammals
Flowering Plants were common
during the Cenozoic Era