Earth Sciences 240A

Catastrophic Events in Earth History

Lecture 1

PART A: The Universe, Time and Philosophy: Prerequisite

Big Bang

Created space

Currently expanding

Cosmological redshift (similar to Doppler)

Age: Roughly 20 bya (?)

We use 15-20 (number will change)

Not a homogeneous space

Local expansion; gravitational collapse

The Milky Way Galaxy

Condensed from cold, slowly spinning �cloud� approx. 16 bya

Flattened into spiral disc galaxy

Solar System

Formed roughly 5 bya

Components

Central Sun (99.9% of mass)

Planets: 4 terrestrial planets; 4 jovian planets; (Pluto/Charon pair)

Asteroids and Comets

Origin of Earth-Moon

Earth �born� about 4.5 bya; Originally homogeneous, cold

Growth by accretion; Heated quickly: (1) Radioactivity, (2) Impact kinetic energy

When molten, gravitational collapse of iron

Element segregation: lights up; heavies down

Moon Origin Theories

Sister to Earth; formed at same time from same materials

Inconsistent; different proportions

Formed elsewhere and �captured� by Earth

Inconsistent; Moon/Earth samples have same isotopic compositions

�Spun-off� material from early Earth

Inconsistent; angular momentum data all wrong

Formed from �debris� of gigantic collision between Earth and another early Mars-size planet

Collision Theory

Time: 4.52-4.50 bya

Glancing impact by Earth of Mars-size planet (in unstable orbit)

Both objects melted completely

Iron core of impactor �fell� into Earth

Hot liquid �splash� plus debris accreted to form orbiting Moon

Moon

Very small core

Interior structure determined from seismographs (shock wave study)

Very early volcanoes; probably weak atmosphere then; �dead� for more than 3 billion years.

End Lecture 1