Formation of the Atmosphere and Oceans - WordPress.com
Formation of the Atmosphere and Oceans Chapter 22.3 Earth Science Riddle Formation of the Atmosphere Scientists believe that the atmosphere began to form early in Earths history. Water may have been in asteroids and meteorites that collided with Earth Water vaporized on impact
Hydrogen and Helium may have been present Earths gravity may not have been able to keep their light atomic mass around long Methane and ammonia present were broken down by the suns intense ultraviolet rays Outgassing Outgassing is the process where gasses are sent into the atmosphere by volcanoes. After formation of Earth, volcanoes sent gasses into the atmosphere
Extensive volcanic activity=lots of gasses Gasses from volcanoes Water vapor Carbon dioxide Trace amounts of nitrogen Scientists believe the same gasses expelled today are the same as they were on early Earth. Oxygen in the Atmosphere
Oxygen not present in volcanic eruptions Little oxygen in Hadean and Archean atmospheres Oxygen was usually bonded to another element Did not begin to accumulate until early Proterozoic First Oxygen Producers Fossils in Australia and South Africa (oldest fossils 3.5 billion years old)
Were traces of threadlike organisms Cyanobacteria Used photosynthesis Use light to produce energy- oxygen is a biproduct Stromatolites Large coral reef-like mounds of cyanobacteria.
Dominated shallow oceans that covered most of Earths continents Made by billions of cyanobacteria colonies that trap and bind sediments together Todays stromatolites found in Glacier National Park are believed to be similar to the ones during the Precambrian stromatolites Evidence in Rocks Oxidized iron in Archean rocks are clues to scientists about the presence of oxygen on early Earth Iron reacts with oxygen to form iron oxides
Rust Absence of iron oxide in Archean rocks indicate there was no oxygen in the atmosphere Banded Iron Banded-iron formations
Localized areas where cynobacteria increased oxygen gas levels to produce iron oxide Formations alternate bands of iron oxide and chert- an iron poor sedimentary rock Iron appears to appear cyclically Possible seasonal changes These formations are now mined for iron Red Beds Rocks beginning about 1.8 bya
Rusty red in color Evidence of red beds in midProterozoic and younger rocks suggest oxygen in the atmosphere Importance of Oxygen Animals require it Provides protection from ultraviolet radiation Today only a fraction of the Suns UV radiation reaches the Earth
Ozone is three oxygen molecules bonded together This ozone layer is what protects us from harmful UV radiation Formation of Oceans Scientist believe oceans reached their current size very early Two sources of water for oceans
Volcanic outgassing asteroids, meteorites, comets that bombarded Earth Precambrian atmosphere rich with water vapor As Earth cooled, the water vapor condensed Rain As liquid water formed Large amounts of rain fell
Filled low lying areas Oceans Rivers The rain mixed with soluble minerals Runoff went to ocean Salty Water and Life Early Precambrian
Inhospitable No life Late Precambrian Covered with oceans Cyanobacteria and other life forms Water and Life Scientists think that Earth is not the
only object in the solar system that contains or has contained water Asteroid Ceres contained more water than Earth Mars has formations that appear to have been carved by water Moons of Saturn and Jupiter might contain water in their interiors Water and Life Life on Earth is in every environment that contains water
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