Do Now What does it mean for a system to be in dynamic balance? How do Greenhouse Gases (GHGs) influence Earth’s atmospheric temperature? What is the Albedo effect? How does Carbon flow from the lithosphere to the atmosphere in the Carbon Cycle?

Essential Questions How did Earth’s atmosphere form? How are CO2 levels kept in dynamic balance? How was Earth’s atmosphere oxygenated? SWBAT describe how Earth’s atmosphere has changed over time.

EQ1: How did Earth’s atmosphere form?

Accretion forms Earth

Millions of comets bring water

Bombardment ends. Surface cools. Volcanoes form. Rain  Oceans.

Volcanic Outgassing creates atmosphere (CO2, CH4, NH3, H2O)

Check for Understanding Where did Earth’s water come from? How did Earth’s oceans form? How did Earth’s atmosphere form?

EQ2: How are CO2 levels kept in dynamic balance?

Volcanic Outgassing creates atmosphere (CO2, CH4, NH3, H2O)

Earth’s Carbon Cycle recycles outgassed GHGs (dynamic balance)

Silicate Rock Weathering (part of Carbon Cycle)

Step 1: Volcanoes outgas CO2

Step 2: Rain carries CO2 & weathers Silicon-based rocks 1 2

Step 3: Weathered sediments settle under ocean & compact into rocks 1 2 3

Step 4: Carbonate rocks subducted 1 2 3 4

Maintains dynamic balance of CO2 in atmosphere. Acts like a thermostat. 1 2 3 4

Snowball Earth: Testing the Thermostat (2.2 BYA, 700 MYA & 500 MYA)

Continents near equator  very large icecaps

Runaway Ice-Albedo Effect  Snowball Earth

BUT outgassing continues BUT outgassing continues. Atmospheric CO2 levels rise (no rain) & trap heat. Snowball melts.

Check for Understanding How has Earth avoided becoming too cold (Mars) or too hot (Venus)? How are CO2 levels in Earth’s atmosphere kept in dynamic balance? How did Earth become a Snowball, and how was it restored?

EQ3: How was Earth’s atmosphere oxygenated?

Earth’s early (Archean) atmosphere: no Oxygen

Cyanobacteria (blue-green algae) were earliest organisms to photosynthesize.

Cyanobacteria’s photosynthesis released O2 to oxygenate atmosphere

Snowball Earths: associated w/ jumps in O2 levels (unknown reasons)

Oxygen levels are in dynamic balance today

Check for Understanding What was Earth’s Archean atmosphere like? How was Earth’s atmosphere oxygenated?