Lecture 3 Planet Earth

							 Lecture 3
Planet Earth




  Copyright Len Bruton   1
                  Lecture 3 – Planet Earth


 Solar nebula accreted to form the solar system
 Earth accreted (probably from solar nebula) about 4,600 million
(i.e. 4.6 billion) years ago due to electromagentic and gravitational
forces – self organization
 Earth is the third planet out from the Sun
 Diameter of 12,776 kilometers
 Earth is much smaller that Jupiter, Saturn, Uranus and Neptune
 Geologic record begins 3,900 million (3.9 billion) years ago




                            Copyright Len Bruton                  2
              Lecture 3 – Planet Earth


 Early Earth, over 4 billion years ago, was molten and
meteorites impacted the surface
 Lighter liquids floated to the surface
 Heavier liquids sank to core, such as iron and nickel
 Lighter liquids gassed out of volcanoes and formed
early atmosphere
 Stable crust formed at surface



                       Copyright Len Bruton           3
     Lecture 3 – Planet Earth - 0 to 3.5 billion
                       years

 Early atmospheric gases from volcanoes were probably carbon
dioxide, carbon monoxide, water vapour (i.e. steam) and methane -
but no oxygen. A hot humid and violent place.
 Earth has a solid crust on a molten liquid core
 The crust is segmented into floating continental plates
 The molten core drove continental drift in a process called
tectonics
 Read the excellent description of Continental Drift at NASA
 Animation of Continental Drift over last 800 million years



                          Copyright Len Bruton                4
 Lecture 3 – Planet Earth - 0 to 3.5 billion years

 As the Earth cooled to below 100 degree
centigrade, water vapour from volcanoes
probably condensed out to form oceans
 Early Earth life may have started without
oxygen, in the seas – algae over 3,500
thousand years (about 3.5 billion years) ago –
that is, life had already started by 30% of the
current age of the Earth                          Cyanobacteria
 The Panspermia theory – Life may have
kick-started outside Earth



                           Copyright Len Bruton               5
               Lecture 3 – Planet Earth
               The Current Composition
 The crust is very thin – only 1/500 th of the diameter




                       Copyright Len Bruton                6
       Lecture 3 – Planet Earth – the Last 500
                    million Years
 Photons from the Sun are thought to have provided the energy
for water vapour to split into oxygen and hydrogen leading to
oxygen-feeding life forms about 2 thousand million (i.e. billion)
years ago
 Starting about 500 million years ago, the oceans became steady-
state chemical sources of life
 Two-thirds of the Earth is covered by the oceans
 The sea floor spreads and continents drift on their plates
 The molten core causes a magnetic field around Earth which
protect Earth from radiation and allowed the atmosphere to
develop


                          Copyright Len Bruton                7
       Lecture 3 – Planet Earth – the Last 500
                    million Years
 Periodic Ice Ages have occurred over these 500 million years
 Outstanding detailed slide presentation of The Ice Ages




                          Copyright Len Bruton                   8
   Lecture 3 – Planet Earth – The Last 150,000
       Years of Unsettling Climatic Years



 Dramatic climate changes have occurred from full Ice
Ages and glacial coverage to non-glacial warm periods
 Transitions from Ice Age to warm periods have
occurred in less than 10,000 years and we do not know
the reasons.




                      Copyright Len Bruton          9
Lecture 3 – Planet Earth – The Last 150,000
    Years of Unsettling Climatic Years




                Copyright Len Bruton          10
   Lecture 3 – Planet Earth – The Last 150,000
       Years of Unsettling Climatic Years
 Solar variations, volcanic activity, space dust,
asteroids, etc. are theories that might be the reason
 Humans have expanded across the planet since the
last Ice Age, over the last 20,000 years, taking advantage
of the highly favourable period between Ice Ages
 Excellent article relating human development and ice
ages: Ice Ages and Big Brains: Climate Change and
Human Evolution



                       Copyright Len Bruton           11