Earth 2

Tuesday, March 16th, 1999
Announcements: Thursday's test is postponed until next Tuesday!

Lecture notes:
ABRUPT CHANGES AFFECTING THE EARTH

Extinction

Time periods in which a significant organism never crosses earth again

Look at the distributions of families of organisms--2-4 families of organisms become extinct during significant periods of geologic time

The Revolutionary Clock changed at 240 million years...Ancient life, Middle Life, and Modern Life

250 million years ago, 200 families of organisms became extinct each time period

K-T Boundary

Came into existence 65 million years ago

Known as the Cretaceous-Tertiary Boundary (K-T Boundary)

Organisms that became extinct:

• plankton
• autotrophs
• follow down the food chain
• "benthos"--bottom dwelling organisms became extinct in coastal areas
• benthos exception: detritus feeders
• large land animals over 25 kg died
• large land animal exception: trees survived

This extinction occurred faster than it can be resolved. Sediments are mixed by organisms distinguishable only in intervals of 10 K years therefore, this must have happened within the order of thousands of years or less

One scientist said this extinction occurred in the spring time 65 million years ago--months, days, years...

Causes of Extinction

1) CO2 Injection Event--the planet's slowly getting cooler-->Deccan Traps formed, lava flows-->Earth "burped" and filled the atmosphere with so much CO2 there was a catastrophic warming event on Earth

2) Freshwater Injection--Arctic Ocean spilled out freshwater, putting a freshwater cap on the ocean-->killing plankton/marine organisms-->Land Animals live

3) Impact Event (A. Comet)--This comet acts like a "poison" to the earth, affecting all organisms in different ways (B. Asteroid)--A significant large body known as a bollide

1) 700 Earth Crossings--> 7 w/ diam = 10 km (VERY LARGE)

2) 7 km-->200 km = diam...enough iridium in atmosphere

3) 25-100 million years from now Earth should be hit with one of three asteroids

Iridium was also found in Earth's crust...1/10 part per billion.

• Explained by volcanoes with iridium...only explanaiton is extraterrestrial bodies that have this same amount of iridium
• Krakatoa is an example of one of these volcanoes--which filled the stratosphere so full of dust that it circled Earth for several years

Asteroids are much stronger than these volcanoes...they can block the sun for many years, not allowing it to penetrate all the dust and causing the earth's surface to get darker

Questions

Where's this crater supposedly brought about by the asteroid?

Could it be in the ocean where nobody would see it?

The Yucatan Peninsula has a crater that's dated back about 65 million years

Lessons of Earth's Geologic History

1) Billions of Years

• Potent Negative Feedback (Rock Weathering)

2) 10's of Millions of Years

• Major ice cap (30% Earth's Surface) to no ice on the planet
• CO2 / Plate Tectonics Implicated

3) 10's of Thousands of Years

• No Feedback Recorded

4) Abrupt Changes

• Asteroid Theory

*THIS SHOWS THAT THE EARTH HAS REMARKABLE STABILITY!!!

*CHANGE IS NORMAL ON EARTH

*CO2 IS ALWAYS INVOLVED

Natural Variability

• Variability without human association
• Interannual changes from year to year
• Decadal changes--Century changes

Why?

• Solar Variations...order of 1/10%
• Volcanism...stratosphere fills with dust, dust settles, and earth cools

Deterministic cause for every problem

• Everything's a result of force
• Climate determined by forcing factor

Maybe some changes aren't forced...Natural Variability produces these interactions

• ATMOSPHERE--days, weeks
• OCEAN--seasons-->thousands of years
• BIOSPHERE--century
• ICE CAPS--many
• LITHOSPHERE--tens of thousands of years

Think of Earth in this analogy

The earth is a spring with a weight attached. The weight mirrors the mass of the atmosphere. When the weight is pulled down upon, the spring is sent into motion...eventually decaying through time

Sometimes different changes cancel themselves out or produce even more dramatic changes