A SHORT LOOK AT EARTH HISTORY

FORMATION OF UNIVERSE

Formation of Universe: 13-20 billion years Big Bang Theory

Formation of Galaxy: 11 billion Years Formation of Solar System: 4.6 billion

years Probably takes 10-100 million years for

planets to form

BIG BANG THEORY

FORMATION OF SOLAR SYSTEM

FORMATION OF SOLAR SYSTEM 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 970 (973 as of 9/14/13) extrasolar

planets known 262 may be habitable planets

Most known are Jupiter-size planets, larger and easier seen

Super-Earths actually outnumber giant planets

OR IS IT TYPICAL?

THE MILKY WAY

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 How do objects the size of a refrigerator hold

together? As planets get bigger, gravity gets stronger,

impacts get more violent Big impacts throw out ejecta, trap heat Magma ocean Formation of core early in earth history as iron

sinks

FORMATION OF EARTH

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? Fission? Capture?

COLLISION Over 4 billion years ago 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

COLLISION

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

GEOLOGIC TIME SCALE

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% less bright Evidence for liquid water from very early

on

ORIGIN OF THE OCEANS

Earth the Biography: Origin of the Oceans

MAJOR EVENTS IN THE HISTORY OF LIFE Oxygen levels in atmosphere

Plants release waste oxygen Eventually organisms developed a way to

utilize oxygen Sex: Who Needs It? We are a team: Mitochondria Snowball Earth: what survived and

how? Cambrian "Explosion"

SNOWBALL EARTH

CAMBRIAN EXPLOSION

MASS EXTINCTIONS

CAUSES ?

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

EARTH HISTORY

The Early Earth and Plate Tectonics