Earth 2

Thursday, February 18th, 1999
Announcements:

Lecture notes:

• Our planet has been stable for billions of years.
• When broken down into different time frames, we can see how different the earth used to be.
• Tens of thousands of years ago the earth's system was very sensitive to something.
• The earth was affected by very abrupt changes.
• Many lessons can be learned from looking at the past.

FAINT EARLY SUN PARADOX

• This implies that the universe was formed about 15 million years ago.
• Dust, gravity, etc. forms the planets & stars...Hydrogen & Water Vapor escape forming crust.
• This occurred fairly early on because of bombing, heating, and segregation.
• This occurred early in the 4.6 billion years because we have an atmosphere and an ocean.

SOLAR EVOLUTION

• When the sun's temperature < 50 C...Hydrogen fuses --> Helium. This fusion process creates energy.
• 4H --> 1 Helium + Energy. This creates a star with fewer particles and more mass.
• Gravitational Contraction --> Heating --> Hotter Sun
• This is known as the Main Sequence Evolution of a star
• The sun's heat becomes more intense over time.
• The sun was 70% of what it is today 3.5 billion years ago.

SAGEN & MULLEN'S THEORY

• If the sun is on the main sequence & H-->He, the sun is getting more intense...therefore the earth must have been frozen--a runaway ice house.
• The earth only got out of this runaway ice house 2 billion years ago.

EVIDENCE THE EARTH WAS NOT FROZEN

• Running Water...3.2 billion years ago, the water was not frosen, not boiling. The temperature was between 0 - 100 C. This was known as the Archean Time Period.
• Prokaryota...early signs of signs of life lacking a nucleus. These may be more temperature insensitive than life forms of today. The temperature was between 0 - 70 C.
• Eukaryota & Metazoan...mroe regulated by temperature than the prokaryotas. The temperature was between 0 - 50 C.
• Evaporites...this is the mineral that is formed when sea water is evaporated (ex. table salt). Proves that water had to be liquid. The temperature was between 0 - 58 C.
• Glacial Deposits...moraines are piles of glacial debris that are ripped apart by ice. The first signs of this ice were 2.5 billion yeras ago.
• Oxygen Isotopes...Oxygen had different mass numbers: O16, O17, O18. The temperature was below 40 C.

FAINT EARLY SUN PARADOX

• This said that the earth must be frozen...geologists say no way!

POSSIBLE SOLUTIONS

• Ein = Eout does not work because 1) Astronomy is wrong 2) Continentality (smaller continent means a warmer planet) 3) Clouds
• Heat of Accretion...more heat coming from Earth's interior (100x's greater than today). however it is too small! (it's in microwatts--we need hundreds of watts)
• Rotation Rate of Earth...earth transports momentum to the moon and the moon retreats.
• Change the Composition of the Atmosphere...Volcanic Eruptions???
• Greenhouse Gases (this is the correct answer!!!)

SUMMARY

• The sun is weaker by 30%-->earth is very stable and something is promoting stability.
• Think about these problems in regards tot he energy balance equation.
• Eliminate all possibilities except greenhouse composition difference...REMEMBER: sun keeps getting hotter & hotter.