| − | There is significant uncertainty to what the primitive atmosphere was composed of.<ref name="Bada2013" /> The Miller-Urey experiment assumed an a primitive atmosphere was composed of ''reducing'' (oxygen poor) gases [e.g. methane (CH<sub>4</sub>), ammonia (NH<sub>3</sub>), hydrogen (H<sub>2</sub>), and water vapor (H<sub>2</sub>O)], but by the 1980s geochemists believed that early earth atmospheres probably had ''neutral'' gases like those emitted by volcanoes [e.g. water vapor (H<sub>2</sub>O), carbon dioxide (CO<sub>2</sub>), and nitrogen (N<sub>2</sub>)] and perhaps some ''reducing'' gases like carbon monoxide (CO). Since hydrogen was a light element, there probably would not have been any in early earth.<ref name="wells" /><ref name="Bada2013" /> A possible source of lightning could have been "volcanic lightning", which occurs sometimes near volcanic eruption plumes.<ref name="Bada2013" /> | + | There is significant uncertainty to what the primitive atmosphere was composed of.<ref name="Bada2013" /> The Miller-Urey experiment assumed an a primitive atmosphere was composed of ''reducing'' (oxygen poor) gases [e.g. methane (CH<sub>4</sub>), ammonia (NH<sub>3</sub>), hydrogen (H<sub>2</sub>), and water vapor (H<sub>2</sub>O)], but by the 1980s geochemists believed that early earth atmospheres probably had ''neutral'' gases like those emitted by volcanoes [e.g. water vapor (H<sub>2</sub>O), carbon dioxide (CO<sub>2</sub>), and nitrogen (N<sub>2</sub>)] and perhaps some ''reducing'' gases like carbon monoxide (CO). Since hydrogen was a light element, there probably would not have been any or perhaps very little in early earth.<ref name="wells" /><ref name="Bada2013" /> A possible source of lightning could have been "volcanic lightning", which occurs sometimes near volcanic eruption plumes.<ref name="Bada2013" /> |
| | Some scientists believe that early earth atmosphere was similar to earth today.<ref>[https://web.archive.org/web/20250902132614/https://astrobiology.nasa.gov/news/earths-early-atmosphere-an-update/ Earth's Early Atmosphere: An Update] - NASA</ref> | | Some scientists believe that early earth atmosphere was similar to earth today.<ref>[https://web.archive.org/web/20250902132614/https://astrobiology.nasa.gov/news/earths-early-atmosphere-an-update/ Earth's Early Atmosphere: An Update] - NASA</ref> |