1. Unit 3: THE HISTORY OF THE EARTH

2. Index
1. The Formation of the Solar System
2. The Age of the Earth
3. Fossils
4. The Changing Earth
5. The Earth’s history
6. Life of Earth

3. The Sun and the planets were formed at the same time. There are some evidences:
 All the planets move around the Sun on the same ecliptic plane
 The planets move around the Sun in the same direction (counter-clockwise) and
the Sun revolves in the same direction, too.

4. Materials have been
distributed by the gravity
depending on their
melting point:
The ones that have a high
melting point (refractory)
are close to the Sun 
INNER PLANETS
Mercury Venus Earth Mars
The ones that have a low
melting point (volatile)
are further away 
OUTER PLANETS
Jupiter Saturn Uranus Neptune

5. After the Big Bang matter was concentrated in
different points, forming stars and nebulas (dust +
gas).
1. A star exploded becoming
a supernova
2. A nebula appeared
3. The nebula rotated aund
flattened into a disc shape
4. The temperature rose due
to particles colliding. Nuclear
fusion began in the centre
The Sun appeared

6. The temperature
decreased and
materials condensed
the most refractory
near the Sun
INNER PLANETS
The most volatile far
away from the Sun
OUTER PLANETS
These materials (PLANETESIMALS) were joining together until the planets formed. This
process is called PLANETESIMAL ACCRETION

7. The heat generated melted much of
the planet
Metallic
materials
(denser)
CORE
Silicated
materials
CRUST
Gas
ATMOSPHERE
Activities 1, 2, 3, 4 page 51

8. Previous hypothesis
(nowadays NOT
accepted)about the
age of the Earth
James Ussher (17th
century)
4000 b.C
Lord Kelvin (19th
century)
40 million years
John Joly (19th
century)
100 million years

9. CURRENT ESTIMATION  4550 million years
DATING = It consists of estimating the age of an event or object or placing it in a
specific time or period.
Rock, fossil…

10. Dating methods in
geology
Absolute dating
They determine the age
of the events or
materials
Relative dating
They put materials or
events in chronological
order without specifying
exact dates
Example 1 : Put the next events in chronological order:
B
A
C
D
E
Solution: A, B, C, D, E, erosion

11. Example 2 : Put the next events in chronological order:
Solution: 1, 2, 3, normal fault, erosion, 4
Solution: pink, red, erosion, orange, yellow, blue

12.  Absolute dating methods: RADIOMETRIC DATING
Method used to date an object by comparing the number of
specific radiactive isotopes it contains
Some atoms lose particles from their nucleus in a process of disintegration.
This process happens at fixed speeds.

13. (período de semidesintegración)
The speed of disintegration is expressed as the HALF LIFE (T) of a substance. It is
the time required for half of a mass of radiactive isotopes to disintegrate.

15.  Relative dating methods
The deposit of layers (or sedimentation) happens periodically.
The layers are deposited horizontally and have the same age in the whole layer.
Principles
Principle of superposition
Each layer is younger than the one below it and older
than the one above it
Principle of cross-cutting relationships
An event (fault, fold…) is younger than the rocks it
affected and older than the rocks it did not affect
Principle of faunal succession
The fossils contained in one layer are the same age as
the layer. So, each period in the history of the Earth
can be classified by a type of fossil Activities 5 and 6 page 51

16. PALEONTOLOGY = It is the part of geology that studies fossils.
FOSSILS = They are the remains of living beings or their activity
preserved in rocks.
Fossilization (it is a rare ocurrence)
An organism dies and its body lays on the ground
The soft parts are decomposed
Sediments cover the remains
Diagenesis takes place and the minerals of the sediments substitute
the atoms of the bones, shell…
The sedimentary rock is eroded and the fossil appears uncovered

17. Importance of
fossils
They provide temporal
information
A fossil species will only
appear in rocks for a
specific period of time
(when it lived)
They provide
paleoecological
information
Learn about the
environmental
conditions of a
particular age
INDEX FOSSILS
(fósiles-guía): fossils of
species that existed for
short periods of time
over large areas
Trilobites, ammonites
Ammonite Trilobite

18. MAIN INDEX FOSSILS
trilobites ammonites nummulites
Paleozoic Mesozoic Cenozoic

19. Theories in the
18th-19th
centuries
Catastrophism
(Cuvier)
Isostatic movements, erosion….
There have been sudden
catastrophes that, in a
short space of time, have
changed the Earth
completely
Uniformitarianism
(Lyell)
Slow and imperceptible
changes over millions of
years produce enormous
alterations.
“The same geological
processes that are
observable today were
also responsible for the
changes on Earth in the
past

20. Theories accepted today:
• The changes on the Earth’s surface are mostly
gradual
• There are rare violent events which can also
affect the planet
Types of changes
Climate changes Warm periods/glacial
periods
Sea level changes More or less land
exposed
Palaeogeographic
changes
Changes in the
distribution of the
continents due to
plate tectonics
Changes in
biodiversity
Sudden, massive
extinctions

21. Climate changes

22. Sea level changes

23. Palaeogeographic
changes

24. Graptolites
Changes in
biodiversity

25. Based on the great changes that took place in the past, geologists have divided the
geological time (more than 4500 million years) into units:
EONS ERAS PERIODS
Hadean
Archaean Pre-Cambrian
Proteozoic
Phanerozoic
Paleozoic
Cambrian
Ordovician
Silurian
Devonian
Carboniferous
Permian
Mesozoic
Triassic
Jurasic
Cretaceous
Cenozoic Tertiary
Quaternary
Present Day

26. Geological time, condensed in a diagram displaying the relative lengths of the eons of Earth's history

27.  First rocks, first atmosphere and oceans were formed
 Many meteorites bombarded the Earth
 Lots of volcanic activity
 First life forms probably existed at the end of the Eon

28.  Most of the Earth was an ocean. Microcontinents.
 First prokaryote cells.
Arqueobacteria

29.  Meteorite bombardment stopped.
 Tectonic plate movement began.
 1000 Ma ago one supercontinent (Rodinia) was formed.
 Cryogenian period  coldest period of the planet’s history (tillites have been found
in almost all continents).
 Oxygen appeared:

30.  Cyanobacteria appeared (autotrophic cells which formed rocks called stromatolites).
They did photosynthesis  oxygen is accumulated in the atmosphere 
Aerobians appeared  first eukaryotic cells  first multicellular organisms
 Ediacaran fauna  soft bodied organisms found in Australia

31. Activities 7, 8, 10, 12, 13, 14, 15 page 57
Ediacaran fauna
Rodinia

32. At the beginning (Cambrian) continents were separated.
They reunited in the Permian forming Pangaea.
Caledonian orogeny
+
Hercynian orogeny
 First plants appeared on the land, followed by arthropods, amphibians and reptiles.
 Many new species and extinctions.
 Carboniferous: forest of giant ferns  coal.
 Typical fossils:
 trilobites
 giant ferns
 graptolites
Lepidodendron
Trilobites
INDEX FOSSIL: TRILOBITES

33. Orthoceras Calceola
Annularia
Paleozoic Fossils
Graptolite

34.  Continents separated to reach their current location.
 Warm climate.
 Rise in the global sea level  half of the continents were submerged  they were
covered by limestone and plankton  PETROLEUM
 250 Ma ago: trilobites extinction
 656 Ma ago: dinosaurs + ammonites extinction, probably caused by a meteorite.
 Reptiles were the dominant animals  “Age of Reptiles”.
 First mammals and first birds, first plants with flowers.
INDEX FOSSIL: AMMONITE AND BELEMNITES

35. Belemnite
Mesozoic Fossils
Ammonite

36. Tyranosaurus
Mesozoic Fossils
Pterosaurus Mesasaurus

37.  Alpine Orogeny
 Climate cooled
 Glacial + short interglacial periods  many changes in the sea level
 Dominant living beings: mammals and flowering plants
INDEX FOSSIL: NUMMULITES
Smilodon (sabre-toothed) in America
Australopithecus

38. Nummulites
Carcharodon
Mamut
Cenozoic Fossils
Page 61 activities 17, 18, 19, 24, 25

39. EON ERA PERIOD AGE LIFE FORMS AND FOSSILS GEOLOGY CLIMATE AND
ATMOSPHERE
PHANEROZOIC CENOZOIC QUATERNARY
65 Ma
First hominids
“Age of Mammals and Birds”
Alpine Orogeny
Glacial +
Interglacial
periods
TERTIARY
MESOZOIC CRETACEOUS
250 Ma
First Angiosperms
First Birds
First Mammals
“Age of Reptiles”
Current location of
continents
Rise in the sea level
(petroleum)
Warm Climate
JURASSIC
TRIASSIC
PALAEOZOIC PERMIAN
540 Ma
Forest of giant ferns (coal)
First Reptiles
First Amphibians
First Fish
First Arthropods
Pangea
Hercynian Orogeny
Caledonian Orogeny
Continents were
separated
Glacial Period
Glacial Period
CARBONIFEROUS
DEVONIAN
SILURIAN
ORDOVICIAN
CAMBRIAN
PROTEROZOIC PRE-CAMBRIAN
2500 Ma
First eukaryotic cells
First aerobians
Cyanobacteria
Rodinia
Cryogenian
period
Atmosphere
with oxygen
ARCHAEAN First prokaryotic cells Microcontinents
HADEAN
4500 Ma
First biomolecules First rocks
Meteorites
Volcanic activity
First
atmosphere
(without
oxygen)