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 Earth’s history. Water may have been in asteroids and meteorites that collided with Earth Water vaporized on impact Hydrogen and Helium may have been present Earth’s gravity may not have been able to keep their light atomic mass around long Methane and ammonia present were broken down by the sun’s 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 bi-product

Stromatolites Large coral reef-like mounds of cyanobacteria. Dominated shallow oceans that covered most of Earth’s continents Made by billions of cyanobacteria colonies that trap and bind sediments together Today’s 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 mid-Proterozoic 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 Sun’s 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 Late Precambrian Inhospitable No life 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 Polar ice caps Deep ocean vents