1. Copyright Len Bruton1 Lecture 3 Planet Earth

2. Copyright Len Bruton2 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

3. Copyright Len Bruton3 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

4. Copyright Len Bruton4 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 NASAContinental Drift  Animation of Continental Drift over last 800 million yearsAnimation of Continental Drift

5. Copyright Len Bruton5 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 Earthin the seas  The Panspermia theory – Life may have kick-started outside EarthLife may have kick-started outside Earth Cyanobacteria

6. Copyright Len Bruton6 Lecture 3 – Planet Earth The Current Composition  The crust is very thin – only 1/500 th of the diameter

7. Copyright Len Bruton7 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

8. Copyright Len Bruton8 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 AgesThe Ice Ages

9. Copyright Len Bruton9 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.

10. Copyright Len Bruton10 Lecture 3 – Planet Earth – The Last 150,000 Years of Unsettling Climatic Years

11. Copyright Len Bruton11 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 EvolutionIce Ages and Big Brains: Climate Change and Human Evolution