Earth 2

Thursday, February 25th, 1999
Announcements: Tests were returned and the second part of our textbook was picked up.

Lecture notes:

CLIMATE VARIATIONS TENS OF MILLIONS OF YEARS AGO

• Shows that the earth's climate was far from stable tens of millions of years ago

Cold Climate

• Ice covered much of the earth at different points in time--21,000 years ago, 1/3 of the land was covered with ice. 280,000,000 years ago, almost the entire globe was covered with ice
• Grooves and striations show up, proving that ice is ripping up material in the environment
• Materials are picked up by ice and deposited where the ice melts (tills)
• Moraines are found, with unsorted materials and in various sizes
• Dropstones, which fall from the surface, disrupt sediments, and later have layers built upon them over time, are found near glaciers
• Antartica glaciated 28-35 million years ago, Greenland glaciated 3 million years ago
• The world was 3-5 degrees cooler than it is today

Warm Climate

• Uniformitarianism--explains that the present is the key to the past. An organism that likes a certain climate today probably liked the same climate in the past.
• Oxygen Isotopes (016, O17, O18) caused a difference in mass and a difference in behavior in the environment
• 94 million years ago, Chicago had palm trees and Alaska had 420 species of high order plants--today there are none. There muct have been a warm climate in these areas at some point in time
• There was no evidence of ice except for small amounts of sea ice
• The world was 6-12 degrees warmer than it is today

There were 8 big ice episodes, which occur every 2-3 hundred million years. They began over 2.65 billion years ago, and in between each of these episodes, the climate becomes extremely warm.

Mechanisms

Solar Variation...a mixing event in the sun-->disrupted fusion

• When this happens, an ice age occurs
• Does not work because of timing and there is no proof

Galactic Arms

• These arms of full of dust and gases, which cause less sunlight to be absorbed and the climate to be colder
• We just came out of the Orion Arm, meaning we are getting less dust. We go back through the Orion Arm every 1-3 hundred million years, so we would glaciate then
• These solution could 1) cause the planet to be warmer instead of cooler and 2) is confusing because we don't know how many arms are in the galaxy

Change Earth's Orbit

• The earth has a 23 degree orbit
• Maybe there was no tilt, the poles will always have a little sunlight...meaning it always receives a little bit of energy
• In this colder planet, plants are unable to grow

Land at High Latitude

• There is a surface with high albedo snow (GOOD)
• However, there is plenty of time where land at poles has no ice at all (BAD)

No Deserts

• This means there is a high albedo
• Maybe there's a warm time period when the oceans are located in the subtropics

• Land has a high albedo, as do clouds...they even each other out

Flood the Continents

• Land has a higher albedo than water, meaning the planet's warmer when it is more oceanic
• All warm planet-->Higher Sea Level
• Sea Floor Creation speeds up-->used to be made two times faster than it is today. It was 200m higher than sea level

Make Mountains

• In the troposphere, temperature decreases with height, meaning there is a high albedo
• However, many time periods have a high rate of topography and there is no ice present

Volcanic Eruptions

• Volcanic Eruptions fill the strtosphere with dust, reflecting energy to space, causing the planet to cool down
• This dust only lasts for 2-3 years. In order for glaciation to occur, volcanoes would have to be going off extremely fast to keep this amount of dust up

Change Greenhouse Gases

• The amount of CO2 in the atmosphere increased because of the speed of sea floor creation--it's 2-9 times higher than the level of CO2 today
• Warm Time Period-->High Sea Level-->Rapid Sea Floor Spreading-->Lots of volcanic eruptions putting CO2 into the atmosphere
• This CO2 is weathered out

Lessons

• Climate is varied by large amounts-->palm trees in Chicago, plants in Alaska
• Even though many of these ideas are rejected, they all stem from the Energy Balance Equation
• Many mechanisms are capable of causing different variations in the climate
• CO2 is inescapable. The Greenhouse composition greatly affects the climate