Unit 3: THE HISTORY OF THE EARTH

Index1. The Formation of the Solar System2. The Age of the Earth3. Fossils4. The Changing Earth5. The Earth’s history6. Life of Earth

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) andthe Sun revolves in the same direction, too.

Materials have beendistributed by the gravity

depending on theirmelting point:

The ones that have a highmelting point (refractory)

are close to the SunINNER PLANETS

Mercury Venus Earth Mars

The ones that have a lowmelting point (volatile)

are further awayOUTER PLANETS

Jupiter Saturn Uranus Neptune

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

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

The heat generated melted much of the planet

Metallic materials (denser)

CORE

Silicated materials

CRUST

Gas

ATMOSPHERE

Activities 1, 2, 3, 4 page 51

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

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…

Dating methods in geology

Absolute datingThey 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:

A

B

C

D

E

Solution: A, B, C, D, E, erosion

Example 2 : Put the next events in chronological order:

Solution: 1, 2, 3, normal fault, erosion, 4

Solution: pink, red, erosion, orange, yellow, blue

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.

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

(período de semidesintegración)

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.

PrinciplesPrinciple 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

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

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

MAIN INDEX FOSSILS

trilobites ammonites nummulites

Paleozoic Mesozoic Cenozoic

Theories in the18th-19th centuries

Catastrophism(Cuvier)

There have been suddencatastrophes that, in a

short space of time, havechanged the Earth

completely

Uniformitarianism(Lyell)

Slow and imperceptible changes over millions of years produce enormous

alterations.

“The same geological processes that are

observable today werealso responsible for thechanges on Earth in the

past

Isostatic movements, erosion….

Theories accepted today:

• The changes on the Earth’s surface are mostlygradual

• There are rare violent events which can alsoaffect the planet

Types of changes

Climate changesWarm periods/glacial

periods

Sea level changesMore or less land

exposed

Palaeogeographicchanges

Changes in thedistribution of thecontinents due to

plate tectonics

Changes in biodiversity

Sudden, massiveextinctions

Climate changes

Sea level changes

Palaeogeographicchanges

Graptolites

Changes in biodiversity

Based on the great changes that took place in the past, geologists have divided thegeological time (more than 4500 million years) into units:

EONS ERAS PERIODS

HadeanPre-CambrianArchaean

Proteozoic

Phanerozoic

Paleozoic

CambrianOrdovicianSilurianDevonianCarboniferousPermian

MesozoicTriassicJurasicCretaceous

Cenozoic TertiaryQuaternary

Present Day

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

First rocks, first atmosphere and oceans were formedMany meteorites bombarded the Earth Lots of volcanic activity First life forms probably existed at the end of the Eon

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

Arqueobacteria

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:

Cyanobacteria appeared (autotrophic cells which formed rocks called stromatolites).

They did photosynthesis oxygen is accumulated in the atmosphereAerobians appeared first eukaryotic cells first multicellular organisms

Ediacaran fauna soft bodied organisms found in Australia

Ediacaran fauna

Activities 7, 8, 10, 12, 13, 14, 15 page 57

Rodinia

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

LepidodendronTrilobites

INDEX FOSSIL: TRILOBITES

CalceolaOrthoceras

Annularia

Paleozoic Fossils

Graptolite

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

Belemnite

Ammonite

Mesozoic Fossils

MesasaurusPterosaurus

Tyranosaurus

Mesozoic Fossils

Alpine Orogeny Climate cooled Glacial + short interglacial periodsmany changes in the sea level Dominant living beings: mammals and flowering plants

INDEX FOSSIL: NUMMULITES

Smilodon (sabre-toothed) in America

Australopithecus

Nummulites

CarcharodonMamut

Cenozoic Fossils

Page 61 activities 17, 18, 19, 24, 25

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)