EVOLUTION OF EARTH’S ATMOSPHERE Febrys Knolan L. Velasco 8- Mandela

How did Earth’s atmosphere form? When Earth formed 4.6 billion years ago from a hot mix of gases and solids, it had almost no atmosphere. The surface was molten. As Earth cooled, an atmosphere formed mainly from gases spewed from volcanoes. It included hydrogen sulfide, methane, and ten to 200 times as much carbon dioxide as today’s atmosphere. After about half a billion years, Earth’s surface cooled and solidified enough for water to collect on it.

The Earth is the only planet that can sustain life Earth so hospitable to life why are other planets within the solar system considered so inhospitable to life? Earth hospitable to life, the balance of the gasses and chemicals needed to sustain cell life and generation is optimal within the Earth’s atmosphere, the temperature is comfortable enough for the most part to be able to sustain life, water is readily available to maintain appropriate levels of hydration (we are composed of mostly water you know) and all of these elements come together to allow life to flourish. So what is it about the other planets that make them inhospitable to life that resembles the human and animal races that thrive on Earth?

How come other planet’s atmosphere do not support life as we know it? Other planets and moons in our solar system have atmospheres, but none of them could support life as we know it. They are either too dense (as on Venus) or not dense enough (as on Mars), and none of them have much oxygen, the precious gas that we Earth animals need every minute.

First stage in the evolution of Earth’s atmosphere Original atmosphere was probably just hydrogen and helium Molecules of hydrogen and helium move really fast The Early atmosphere was probably dominated at first by water vapor Then the atmosphere was dominated by nitrogen, but there was certainly no oxygen in the early atmosphere.

Second stage in the evolution of Earth’s atmosphere The hydrosphere was formed 4 billion years ago from the condensation of water vapor The remaining oxygen accumulated in the atmosphere As oxygen in the atmosphere increased, CO2 decreased. No free O2 at this time (not found in volcanic gases). Ocean Formation - As the Earth cooled, H2O produced by out gassing could exist as liquid allowing oceans to form. Evidence - pillow basalts, deep marine seds in greenstone belts.

Third present day atmosphere Some oxygen (O2) molecules absorbed energy from the Sun's ultraviolet (UV) rays These atoms combining with remaining oxygen (O2) to form ozone (O3) molecules, which are very effective at absorbing UV rays The thin layer of ozone that surrounds Earth acts as a shield Plants take in carbon dioxide and give off oxygen while animals take in oxygen and give off carbon dioxide Burning things also give off carbon dioxide

References Earth Science, 13th edition by Trabuck et al., 2012 How did Earth’s atmosphere form? by SciJinks It’s all about weather! and NASA or the National Aeronautics and Space Administration (scijinks.jpl.nasa.gov/atmosphere-formation/) The Atmosphere by Georgia Louviere (teachertech.rice.edu/Participants/louviere/history.html) Evolution of the Atmosphere by JM Hayes, Encyclopaedia Britannica (britannica.com/topic/atmosphere