Ess 5 study guide: air- a mixture of gases and suspended particles that surround. Earth: weather- the state of the atmosphere at a given time/space. The 5 factors that define weather: temperature, air pressure, humidity, cloudiness, windspeed and direction, climate- average weather and variability of the atmosphere. Eg: smoke, ice crystals, sea salt crystals, dust, volcanic emissions. Earth"s se(cid:272)o(cid:374)d at(cid:373)osphere- tectonically active: co2, water vapor, sulfur dioxide, volcanic emissions/gases. Earth"s third at(cid:373)osphere- dry, present day: 78. 08% nitrogen, 20. 96% oxygen, 93% argon, . 04% other, variable constituents: h2o and aerosols. What happened to h2o: when the earth cooled, it turned into our oceans, the atmosphere can only hold a small fraction of water vapor from volcanoes, water vapor clouds oceans. Where did o2 come from: bacteria may have appeared as early as 3. 5 billion years ago, 2. 5 billion years ago, photosynthetic organisms started producing oxygen, rocks started to rust.