Transcript A Short Look at Earth History

A Short Look at Earth History
The big perspective of
‘us in the universe’
E&ES 199
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)
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
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
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 a‘Magma 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)
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
• Life not possible until large impacts ceased
(around 4.2 Ga)
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
Early Environments
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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 ==>
deposition of Banded iron Formations (rocks
with thin ‘rust layers’)
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 E&ES199 (the
intellectual view)
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?
• At least around since 3 Ga, probably much
earlier
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"
Mass Extinctions
The next one??
Humans
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Earliest Personkind 6.5 Ma?
Australopithecus > 2 Ma
Homo erectus 1-2 Ma
Homo neanderthalensis 500,00030,000 yr.
• Homo sapiens<100,000 years
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?
• WE CAN DO BETTER