History of Life on Earth Timeline
Marine extinction intensity during the Phanerozoic
Millions of years ago
The blue graph shows the apparent percentage
(not the absolute number) of marine animal genera
becoming extinct during any given time interval.
It does not represent all marine species, just those
that are readily fossilized. The labels of the "Big Five"
extinction events are clickable hyperlinks; see
Extinction event for more details.
(source and image info)
An extinction (level) event (also known as a mass extinction or biotic crisis) is a widespread and rapid
decrease in the amount of life on Earth. Such an event is identified by a sharp change in the diversity and
abundance of macroscopic life. It occurs when the rate of extinction increases with respect to the rate of
speciation. Because the majority of diversity and biomass on Earth is microbial, and thus difficult to measure,
recorded extinction events affect the easily observed, biologically complex component of the biosphere rather
than the total diversity and abundance of life.[1]
Although there are 10–14 million species of life currently on the Earth,[2] more than 99 percent of all species
that ever lived on the planet are estimated to be extinct.[3][4][5] Extinction occurs at an uneven rate. Based on the
fossil record, the background rate of extinctions on Earth is about two to five taxonomic families of marine
invertebrates and vertebrates every million years. Marine fossils are mostly used to measure extinction rates
because of their superior fossil record and stratigraphic range compared to land organisms.
Since life began on Earth, several major mass extinctions have significantly exceeded the background extinction
rate. The most recent, the Cretaceous–Paleogene extinction event, which occurred approximately 66 million
years ago (Ma), was a large-scale mass extinction of animal and plant species in a geologically short period of
time. In the past 540 million years there have been five major events when over 50% of animal species died.
Mass extinctions seem to be a Phanerozoic phenomenon, with extinction rates low before large complex
organisms arose.[6]
Estimates of the number of major mass extinctions in the last 540 million years range from as few as five to
more than twenty. These differences stem from the threshold chosen for describing an extinction event as
"major", and the data chosen to measure past diversity.
The Great Oxygenation Event (GOE), also called the Oxygen Catastrophe, Oxygen Crisis, Oxygen
Holocaust, Oxygen Revolution, or Great Oxidation, was the biologically induced appearance of dioxygen
(O2) in Earth's atmosphere. Geological, isotopic, and chemical evidence suggest that this major environmental
change happened around 2.3 billion years ago (2.3 Ga).[2]
Cyanobacteria, which appeared about 200 million years before the GOE,[3] began producing oxygen by
photosynthesis. Before the GOE, any free oxygen they produced was chemically captured by dissolved iron,
were it settled out of solution as iron oxides or organic matter. The GOE was the point when these oxygen sinks
became saturated and could not capture all of the oxygen that was produced by cyanobacterial photosynthesis.
After the GOE, the excess free oxygen started to accumulate in the atmosphere.
Free oxygen is toxic to obligate anaerobic organisms, and the rising concentrations may have wiped out most of
the Earth's anaerobic inhabitants at the time. Cyanobacteria were therefore responsible for one of the most
significant extinction events in Earth's history. Additionally, the free oxygen reacted with atmospheric methane,
a greenhouse gas, greatly reducing its concentration and triggering the Huronian glaciation, possibly the longest
snowball Earth episode in the Earth's history.[4]
Eventually, aerobic organisms began to evolve, consuming oxygen and bringing about an equilibrium in its
availability. Free oxygen has been an important constituent of the atmosphere ever since.[4]
Event in the
fossil record
Years ago
Earth Forms
Simple cells appear
Cyanobacteria appear
4.6 Ba
3.6 Ba
3.4 Ba
0B
1B
.2B
0cm
50cm
10cm
Great Oxygenation
Event
Eukaryotes appear
2.3 Ba
1.1B
55cm
.3
15cm
Sexual reproduction
arises
Multicellular life
appears
1st animals appear
Bilaterians appears
1.2 Ba
.8B
40cm
1 Ba
.2B
10cm
600 Ma
550 Ma
.4B
.05B
20cm
2.5cm
500 Ma
475 Ma
450-440 Ma
.05B
.025B
.025B
2.5cm
1.25cm
1.25cm
400 Ma
.05B
2.5cm
375-360 Ma
.04B
2.0cm
60-70% of all species
become extinct.
360 Ma
300 Ma
251.4 Ma
0B
.06B
.0486B
0cm
3.0cm
2.43cm
Land/water lifestyle
Lay eggs out of water
~96% of marine
organisms and 70% of
terrestrial organisms
extinct.
Mammals appear
4. Triassic-Jurassic
extinction event
Birds appear
Flowering plants
appear
5. CretaceousPaleogene extinction
event
200 Ma
200 Ma
.0514B
0B
2.57cm
0cm
150 Ma
130 Ma
.05B
.02B
2.5cm
1.0cm
Descended from dinosaurs
Most plant forms we see
today are Angiosperms.
66 Ma
.064B
3.2cm
Primates appear
Hominidae appears
60 Ma
20 Ma
.006B
.04B
.3cm
1.0cm
Genus Homo appears
2.5 Ma
.0175B
.875cm
Anatomically modern
humans appear
250000 Ya to the
present
.00225B
.1125cm
Dinosaurs become extinct,
except for the descendant
birds, as do 75% of other
species.
Monkeys, etc.
Ancestors of the Great
Apes (chimpanzees,
gorillas, and Orangutans)
appear
Direct ancestors of
modern humans evolve in
Africa
Modern humans appear
and colonize the Earth
Fish appear
Land plants appear
1. Ordovician-Silurian
extinction event
Insects & Seeds
appear
2. Late Devonian
extinction event
Amphibians appear
Reptiles appear
3. Permian-Triassic
extinction event
2 Ba
Interval in
years
Scale
distance
Description
The Hadean Era
Prokaryotes (anaerobes)
Great Oxygenation Event:
Many strict anaerobes
perish, Takes ~ 1B years.
Biogenic O2 begins to
collect in the atmosphere.
Cells with membranebound organelles
First animals with a head
end and a tail end.
60-70% of all species
become extinct.
75% of all species become
extinct.
Event in the
fossil record
Years ago
Earth Forms
Simple cells appear
Cyanobacteria appear
Great Oxygenation
Event
Eukaryotes appear
4.6 Ba
3.6 Ba
3.4 Ba
2.3 Ba
Sexual reproduction
arises
Multicellular life
appears
1st animals appear
Bilaterians appears
1.2 Ba
Fish appear
Land plants appear
1. Ordovician-Silurian
extinction event
Insects & Seeds
appear
2. Late Devonian
extinction event
Amphibians appear
Reptiles appear
3. Permian-Triassic
extinction event
2 Ba
Interval in
years
Scale
distance
Description
The Hadean Era
Prokaryotes (anaerobes)
Biogenic O2 begins to
collect in the atmosphere.
Cells with membranebound organelles
1 Ba
600 Ma
550 Ma
500 Ma
475 Ma
450-440 Ma
First animals with an
obvious head end and a
tail end.
60-70% of all species
become extinct.
400 Ma
375-360 Ma
60-70% of all species
become extinct.
360 Ma
300 Ma
251.4 Ma
Land/water lifestyle
Lay eggs out of water
~96% of marine
organisms and 70% of
terrestrial organisms
extinct.
Mammals appear
4. Triassic-Jurassic
extinction event
Birds appear
Flowering plants
appear
5. CretaceousPaleogene extinction
event
200 Ma
200 Ma
Primates appear
Hominidae appears
60 Ma
20 Ma
Genus Homo appears
2.5 Ma
Anatomically modern
humans appear
250000 Ya to the
present
75% of all species become
extinct.
150 Ma
130 Ma
Descended from dinosaurs
Most plant forms we see
today are Angiosperms.
66 Ma
Dinosaurs become extinct,
except for the descendant
birds, as do 75% of other
species.
Monkeys, etc.
Ancestors of the Great
Apes (chimpanzees,
gorillas, and Orangutans)
appear
Direct ancestors of
modern humans evolve in
Africa
Modern humans appear
and colonize the Earth
Timeline of Life History on Earth
NGSS: MS-LS4-1. Analyze and interpret data for patterns in the fossil record that document the existence, diversity, extinction, and
change of life forms throughout the history of life on Earth under the assumption that natural laws operate today as in the past.
Objective: SWBAT complete a timeline of the history of life on Earth and relate the major changes in life to
events in earth history.
Materials: 1-2.5m length of adding machine tape, meterstick, ruler, calculator
Methods: 1. Calculate the interval in billions of years between events in the history of life on Earth and record
in the data table.
2. Calculate the scale distance for each event and record in the data table.
3. Place each event at the correct scale distance on your timeline.
4. Answer the analysis questions using the results from the activity. Answer using complete
sentences.
5. Write a conclusion utilizing the C.E.R model as shown.
Calculations:
Scale=
50cm
1B years
Interval in Billions of years=
previous event - next event
1000000000
Scale distance= scale  time interval
Analysis:
1. Based on the timeline you completed, how have the five mass extinctions in Earth’s history affected the
evolution of life on our planet?
2. Each of the five mass extinction events were responsible for eliminating greater than 60% of the life
forms that existed at that time. How can we use this to explain what happened to life after these
extinction events?
3. The vast majority of life on Earth today requires oxygen to survive. What event in earth history
provided the oxygen that these organisms require?
4. These dates and events are determined by careful examination of the fossil record. How can we be sure
that the dinosaurs actually went extinct in the Cretaceous-Paleogene extinction event? What would
provide evidence that they survived beyond that event?
5. What happened to the first oxygen that was produced by the Cyanobacteria?
6. What is the definition of Phanerozoic?
Conclusion: Claim-Evidence-Reasoning model