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