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 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 O 2 –Eventually other organisms developed a way to live with/utilize O 2 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 Earliest Personkind 6.5 Ma? Australopithecus > 2 Ma Homo erectus 1-2 Ma Homo neanderthalensis 500, ,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