A Short Look at Earth History

1
A Short Look at Earth History

• The big perspective of
• us in the universe
• EES 199

2
Formation of Everything

• Formation of Universe (Big Bang) 15 Ga (making
  H, He , little bit of Li, B, Be)
• Element formation (inside stars up to Iron,
  during supernovas the heavier elements,
  radioactive decay makes a few more)
• Formation of Galaxy 11 Ga
• Formation of Solar System (includes earth) 4.6
  Ga
• Sun is probably a third generation star
  (initially feeble)

3
Formation of Planets

• Planets made of same material as Sun, minus
  elements that remain mostly in gases
• Inner Rocky Planets (M, V, E, M) iron and
  magnesium silicates
• Outer gas giants (J,S,U,N) and moons H, He,
  water, ice

4
Our Solar System is Not Unique(but we are)

• Over 100 extra-solar planets known
• We can barely detect Jupiter-sized planets, no
  technology yet available to see small planets

5
Formation of Earth

• Planets formed by accretion of smaller objects
  impacts/clustering of planetesimals
• When planets got bigger, gravity got stronger,
  and planets sweep up surrounding debris
• Early earth heats up and aMagma ocean formed
• Formation of core early in earth history as iron
  sank to the center, and frothy light stuff
  floated to the surface (continents)
• Core formation associated with catastrophic
  degassing of the early atmosphere (Big Burp)

6
Unstable Early Earth

• There may have been several moon-forming events
  through mega-impacts
• 1000-km impactors can melt crust
• 100-km impactors create temporary atmosphere of
  vaporized rock, vaporize oceans
• Sustained life not possible until large impacts
  ceased (around 4.2 Ga)

7
Conditions on Early Earth

• Oldest existing minerals on earth 4.1 Ga
• Oldest dated rocks 3.9 Ga
• Oxygen-absent early atmosphere (oxygen is created
  by photosynthesizing organisms)
• Faint Early Sun perhaps 30 per cent less bright
• Evidence for liquid water already early on

8
Early Environments

• Very early earth had thin, unstable crust
• Large areas of continental crust by 2.5 Ga
• Plate tectonics since at least two Ga
• Early magmas very hot (up to 1700 C?)
• Early oceans oxygen poor, Fe-rich bottom waters,
  some oxygen in surface waters gt deposition of
  Banded iron Formations (rocks with thin rust
  layers)

9

• What Is Life?
• "Life is what dies when you stomp on it (Dave
  Barry)
• A force that prevents tissue oxidation (JCV)
• A self-replicating chemical system (the common
  non-religious scientific view)
• A force that allows you to take EES199 (the
  intellectual view)

10
How Did Life Originate?

• Simple organic molecules that came with
  meteorites or formed in the early earth?
• Early organisms were extremophilic
  chemoautotrophs?
• Minerals served as catalysts and templates?
• Around since 3 Ga, probably earlier but not
  sustained?

11
Major Events in the History of Life

• Oxygen levels in atmosphere
• Autotrophic organisms release waste O2
• Eventually other organisms developed a way to
  live with/utilize O2
• Snowball Earth (0.8 Ga) why, how did the earth
  recover, and what survived?
• Cambrian (0.5 Ga) "Explosion of life"

12
Mass Extinctions
The next one??
13
Humans

• Earliest Personkind 6.5 Ma?
• Australopithecus gt 2 Ma
• Homo erectus 1-2 Ma
• Homo neanderthalensis 500,000-30,000 yr.
• Homo sapienslt100,000 years

14
THE LAST CHAPTER IN EARTH HISTORY? ANTHROPOGENIC
ENVIRONMENTS

• Kill many beasties and plants - next mass
  extinction?
• Mess up climate - as hot as 55 Ma?
• Pollute the exosphere - unprecedented?
• Exhaust natural resources - unprecedented?
• Overpopulate the globe till we are the only
  species left but unable to take care of business?
• THERE IS A BETTER WAY!