1. UNIT 3
HISTORY OF EARTH

2. The origin of
the Solar
System
1. Supernova
2. Nebula
3. Temperature rose
due to nuclear
fusion reactions
4. Temperature fall
and materials start
condensing
5. Condensed
fragments collided
and got together
until planets were
formed

3. THE SOLAR SYSTEM

4. METHODS OF ABSOLUTE DATING
Absolute dating methods measure the time that
has elapsed since a geologic event happened
(rock formation, deposition of a stratum, the
age of a fossil, etc.).
They are:
SedBiological methods
imentological methods
Radiometric methods

5. Biological methods
These are based on the analysis of biological rhythms
associated with intervals of time, such as the growth rings of
trees or daily growth bands (striations) on living corals.
Each year, trees develop
two rings: one light ring (in
spring) and one dark ring
(in summer). By doing a
very simple calculation,
we can tell the age of a
tree if we count the
number of rings inside the
tree trunk.

6. Sedimentological methods
These are based on cyclical sediment deposits, like what
happens with glacial varves, which are sediments that are
deposited at the bottom of glacial lakes, depending on
seasonal changes.
Summer
Winter
Ice
Glacial lake
Thin dark layer of sediments
Only a thin dark layer (consisting of
clays and organic matter) accumulates
when the surface of the lake is frozen
over in winter.
Thick clear layer of
sediments
Glacial varves
A thick clear detrital
layer is deposited into
the lake when the ice
melts in summer.
It is possible to calculate the age of the lake
by counting the varves.

7. Radiometric methods
Radioactive elements such as uranium 238 (U238) or carbon-14
(14C) are used; they may be contained in rocks, fossils or
archaeological remains.
Radioactive isotopes are unstable and emit radiation, so that
after some time, they transform into other more stable atoms.

8. HALF LIFE OF RADIACTIVE ATOMS
If we know the rate of disintegration, we can date the age of a
sample by measuring the ratio between unstable radioactive
atoms and stable atoms formed from them.

11. METHODS OF RELATIVE DATING
Relative dating consists of ordering the strata or geological
events recorded in one or more stratigraphic series
chronologically, without specifying how long ago they
occurred or how long they lasted.
Relative dating is achieved by interpreting satratigraphic
series, uisng the following basic principles:
Principle of uniformitarism
Principle of the sucession of geological events
Principle of the arrengement of strata
Original horizontality
Lateral continuity
Superposition
Principle of the sucession of fossils

18. The four steps of fossilization
1. Death
2. Burial
3. Replacement
4. Erosion

20. INDEX FOSSILS

21. CATASTROPHISM

22. UNIFORMITARISM

24. GEOLOGIC TIME SCALE

25. The Precambrian Era:
Geological and paleoclimatic events
Hadean era (4,500-3,800 m.y.)
1. Meterorites continually collided the
Earth
2. Layers were formed
3. Atmosphere and oceans were formed
4. The Moon was formed
5. Life appeared at the end of the period
Archaean and Proterozoic (3,800-540 m.y.)
1.
2.
3.
4.
5.
6.
Meteorite bombardment stopped
Tectonic plates movement started
Oxygen appeared in the atmosphere
Iron oxide appeared in rocks
Rodinia supercontinent was formed
The biggest glacial period started

26. The Paleozoic Era:
Geological and paleoclimatic events
• 542 to 500 million years ago, the
continents were separated by shallow,
warm seas.
• 460 to 350 million years ago, the
continents began to come together. The
Caledonian orogeny mountain ranges
formed as a result of several continental
masses colliding and glaciation occurred.
• 300 to 250 million years ago, the
Variscan orogeny mountain-building
event was caused by new continental
collisions. The supercontinent Pangea II
was formed and there was another
glaciation. The climate in the inland
regions of the continent was very dry as it
was very far from the sea. An episode of
massive volcanic activity occurred at the
end of the Permian period that caused
global warming due to increasing
greenhouse gases in the atmosphere.

27. The Mesozoic Era:
Geological and paleoclimatic events
• 250 to 200 million years ago, the continents came together as Pangea II. The climate was very
warm and very dry in the interior of the supercontinent. At the end of the Triassic period, continental
fragmentation began and shallow seas opened up.
• 200 to 145 million years ago, the
opening of the continents
continued. The climate was much
wetter and it was still warm
(tropical to humid temperate
environments).
• 145 to 65 million years ago, the
continents continued to separate
(the Atlantic opened up), but Africa
and India started colliding with
Eurasia, which initiated the uplifting
of the Alpine orogeny mountain
building event. The climate started
to cool. At the end of the
Cretaceous period, global volcanic
activity increased and a large
asteroid struck Earth.

28. The Cenozic Era:
Geological and paleoclimatic events
• 65 to 23 million years ago, the
separation of the continents that
began in the Cretaceous period (the
opening of the Atlantic) continued and
India completed its collision with
Eurasia. This marked the end of the
Alpine orogeny. The mountains on
the western boundary of America
formed. The climate at this time was
still subtropical and humid in almost
all regions.
• 23 to 2.5 million years ago, the
continents reached positions close to
the ones they are in at the present
time. The Red Sea and East Africa's
Great Rift Valley opened. The climate
became cooler and more arid.
• 2.5 to 0 million years ago, several
glacial episodes occurred.

29. The Precambrian Era: Biological events
• 3,800 to 3,500 million years ago, the
earliest life appears on Earth, probably
originating in an aquatic environment.
There are indications of this in the
biochemical clues that appear in rocks
from this time and in the first fossilised
prokaryotes.
• 3,400 million years ago, stromatolites appear.
These are structures produced by the activity
of cyanobacteria. These and other
photoautotroph organisms filled the
atmosphere with oxygen that produced mass
extinction of anaerobic organisms 2,000 million
years ago.
• 1,700 to 1,000 million years ago,
eukaryotes and multicellular organisms
emerge.
• 700 to 542 million years ago, mass extinctions occur during glaciations and a subsequent explosion
of biodiversity takes place. In the Proterozoic formations in Ediacara (Australia), fossils of beings
similar to simple animals appear (some different from existing groups and others such as sponges,
jellyfish and worms).

30. Ediacaran fauna

31. The Paleozoic Era: Biological events
• 542 to 460 million years ago, there was a great explosion of marine life. The majority of
invertebrate groups, including the first chordates, appeared.
• 460 to 400 million years ago, fish
appeared. Marine biodiversity decreased
due to the glaciation at the end of the
Ordovician period, but it recovered later.
New groups of fish started showing up.
The first plants and terrestrial arthropods
emerged.
• 400 to 250 million years ago, there was
a great diversity of fish. Plants without
seeds, and later conifers, flourished in the
terrestrial environment. The first
amphibians and early reptiles started
showing up. The latter proliferated and
diversified, adapting better to arid
conditions. At the end of the era, the
greatest mass extinction in the history of
the Earth occurred (90% of species were
wiped out).

32. Life in the Paleozoic Era (540-250 m.y.)
Trilobite
Ferns
Armoured fish
Terrestrial animals

33. The Mesozoic Era: Biological events
• 250 to 200 million years ago, fish and
marine invertebrates recovered from the
Permian extinction. On land, the arid
climate favoured primitive gymnosperms,
insects and reptiles (the latter adapted to all
environments). The first dinosaurs and
early mammals started showing up.
• 200 to 145 million years ago, there was a
great diversity of marine invertebrates.
Fish and marine reptiles dominated the
seas. Conifers dominated the flora and
dinosaurs diversified and reached large
sizes. The first birds appeared.
• 145 to 65 million years ago, there was a great diversity of marine life and dinosaurs. Flowering
plants, pollinating insects and marsupials appeared. The end of the Cretaceous period saw a rapid
mass extinction, especially of many sea creatures, such as the ammonites, and terrestrial creatures
such as dinosaurs.

34. Life in the Mesozoic Era (250-65 m.y.)
Ammonite
Dinosaurs
Gymnosperms

35. The Cenozoic Era: Biological events
• 65 to 23 million years ago, the survivors of the extinction in the Cretaceous period, especially
angiosperm plants, mammals and birds, spread and diversified.
• 2.3 to 2.5 million years ago, birds and
mammals diversified widely, and in
many cases, into large sizes. Many of
the existing groups, including the first
anthropoid primates (and hominids at
end of the period), appeared. A
subtropical humid forest flora dominated
in almost all latitudes, although at the
end of this period the shift towards a
progressively cooler and drier climate
modified the fauna and flora.
• 2.5 to 0 million years ago, glaciations
radically altered the flora and caused
the emergence of many modern
groups of plants. There were new
mammal species adapted to colder or
drier climates. Hominids emerged and
the human species appeared.

36. Life in the Cenozoic Era (65 m.y. – present)
Mammals & birds
Humans
Angiosperms

37. SUMMARY
The Precambrian Era
3500 mya. The first
organisms appear
which are very simple
prokaryotes
3400 mya. First known
cyanobacteria (blue-green
algae) form stromatolites
500 mya. "Ediacara fauna”
the first animals, appear
600 mya. Mass
2000 mya. The
extinction occurs due to
majority of nonglaciations
aerobic organisms
become extinct
3800 mya. Possible
origin of life
2 500 mya
HADEAN EON
ARCHEAN EON
PROTEROZOIC EON
650 mya. The first great
supercontinent known as
Pangea I is formed
542
mya
4 000
mya
4650 mya.
Origin of the
Earth's crust
3500 mya. The
oceans have already 2500 mya. There are
already continental
formed
masses with
sedimentary rock
700 to 580 mya. Global glaciation occurs

38. SUMMARY
The Paleozoic Era
419 mya. Plants and
terrestrial arthropods
emerge. There is a great
diversity of fish.
542 to 460 mya
(million years
ago). There is
an explosion of
marine life.
555 mya. Fish appear.
380 mya. Lobe-finned fish
emerge; they are the
ancestors of tetrapods.
Hallucigenia
Anomalocaris
Fish with jaws
250 mya.
90% of life
forms
become
extinct.
Pteridophytes
(ferns)
predominate.
360 mya. The first
amphibians appear
and predominate.
320 mya.
Reptiles appear
and diversify.
Dimetrodon
Trilobites
Ichthyostega
EON
PALEOZOIC
Cambrian
Ordovician
488
443
500 mya. The continents
have separated.
PHANEROZOIC
Silurian
450 mya. Several continental
masses come together
causing a glaciation and the
Caledonian orogeny.
PALEOZOIC
Devonian Carboniferous Permian
416
359
299
300 mya. The
continents come
together causing
another glaciation
and the Variscan
orogeny.
250 mya. There
is massive
volcanic activity.
250 mya. Another
great supercontinent
known as Pangea II is
formed.

39. SUMMARY
The Mesozoic Era
240 mya. There are reptiles in all
environments. The first dinosaurs and
early mammals start showing up.
250 mya. Marine life
recovers from the extinction
of the Permian Period. On
200 mya.
land, gymnosperms, insects
Gymnosperms dominate.
and reptiles dominate.
80 mya. Dinosaurs
dominate the Earth.
128 mya.
Angiosperms appear.
Pterosaur
160 mya.
Birds
appear.
Apatosaurio
65 mya. Mass extinction
caused by a meteorite
impact occurs.
Triceratops
Allosaurus
Plesiosaur
Tyrannosaurus
Ammonites
Cynodont
Ichthyosaur
EON
MESOZOIC
Triassic
PHANEROZOIC
199
210 mya. Break-up of
Pangea II starts. The
continents separate.
MESOZOIC
Cretaceous
Jurassic
145
140 mya. The opening of
the Atlantic starts.
70 mya. The
Alpine
Orogeny
starts.
65 mya. An enormous meteorite
crashes to Earth, in the Gulf of
Mexico.

40. SUMMARY
The Cenozic Era
60 mya. Populations of
mammals, birds and
angiosperm plants peak.
15 mya. Flora and
fauna alter due to
climate change.
20 mya.
First
anthropoid
primates.
Diatryma
Arsinotherium
Indricotherium
4 mya. Early hominids
appear and evolve into
the human species.
Proconsul
Animals from the Ice Age
PHANEROZOIC EON
CENOZOIC
CENOZOIC
Paleogene
Neogene
23
60 mya. Continental
separation continues.
25 mya. The
Alpine
orogeny
ends.
Quaternary
2,5
10 mya. The Red
Sea and the Great
Rift Valley open.
The continents reach
2 mya. Several
their current positions.
episodes of
glaciations (global
cooling) start.

41. REVISING CONCEPTS

42. A
B

43. B
A

45. Look at the stratigraphic redord of an area. Indicate the
stratigraphic series and the stratigraphic sequences

46. Order the events