A Short Look at Earth History

Formation of Sun Formation of Universe: 13 billion years Formation of Galaxy: 11 billion Years Formation of Solar System: 4.6 billion years Sun is probably a third generation star Probably takes million years for planets to form

Formation of Planets Planets made of same material as Sun, minus elements that remain mostly in gases Inner Rocky Planets: iron and magnesium silicates Outer gas giants and moons: water ice If a protoplanet gets big enough, it can hold everything (Jupiter, Saturn) Very far from sun: methane, ammonia, nitrogen ice

Our Solar System May Not Be Typical Over 200 extrasolar planets known Barely can detect Jupiter-size planets, don't yet have technology to see small planets Many have very eccentric orbits Some have gas giants very close in to sun ("hot Jupiters")

Formation of Earth Planets formed by accretion of smaller objects = impact Very tiny objects hold together by atomic forces Objects kilometers across hold together by gravity As planets get bigger, gravity gets stronger, impacts get more violent Big impacts throw out sediment/rocks, trap heat Magma ocean Formation of core early in earth history as iron sinks

Formation of Moon It's very hard to account for the Moon: –Very big compared to its parent planet –Orbits nearly in plane of earth's orbit, not over equator. Co-creation with Earth? Capture?

Collision Can explain why moon orbits in earth's orbital plane Can explain why moon's composition differs from earth Models of solar system evolution suggest that last stage is mega-collisions Impact would have melted most of earth and moon Earth would have been incandescent for about 10,000 years.

Unstable Early Earth May have been several moon-forming events 1000-km impactors can melt crust 100-km impactors create temporary atmosphere of vaporized rock, vaporize oceans Life not possible until large impacts cease To have life on Earth, we need Jupiter? –Sweeps up debris and reduces impacts –Stabilizes orbits of other planets To have life on Earth, we need Moon? –Stabilizes changes in earth's axis tilt

Conditions on Early Earth Oldest existing earth materials: 4.1 billion years old Oldest rocks: 3.9 billion years old Oxygen-poor atmosphere (present oxygen is created by life) Faint Early Sun: perhaps 30 per cent less bright Evidence for liquid water from very early on

Life What Is It? "Life is what dies when you stomp on it"-- Dave Barry A self-replicating chemical system

How Did Life Originate? Certainly not as complex as anything now alive Lots of candidates for first self-replicators Role of minerals as catalysts and templates? Simplest organisms are extremophiles At least since 3 billion years, probably much earlier

Mass Extinctions

Causes ? Climate Change Disease Mountain-building Sea Level Change Competing Organisms Over-specialization Volcanism Meteor Impact

Humans Australopithecus > 2 m.y. Homo erectus 1-2 m.y. Homo ergaster 1-2 m.y. Homo habilis < 1 m.y. Homo neanderthalensis 500,000-30,000 yr. Homo sapiens<100,000 years

The Geologic Time Scale

Some Geologic Rates Cutting of Grand Canyon 2 km/3 m.y. = 1 cm/15 yr Uplift of Alps 5 km/10 m.y. = 1 cm/20 yr. Opening of Atlantic 5000 km/180 m.y. = 2.8 cm/yr.

Some Geologic Rates Movement of San Andreas Fault 5 cm/yr = 7 m/140 yr. Growth of Mt. St. Helens 3 km/30,000 yr = 10 cm/yr.

1 Second = 1 Year 1 hour+ to pyramids 3 hours to retreat of glaciers from Wisconsin 12 days = 1 million years 2 years to extinction of dinosaurs 31 years = 1 billion years

Were The Dinosaurs Failures? Dinosaurs: 150,000,000 years Recorded History: 5000 years For every year of recorded history, the dinosaurs had 30,000 years For every day of recorded history, the dinosaurs had 82 years For every minute of recorded history, the dinosaurs had three weeks