1. Formation of the Atmosphere and Oceans
Chapter 22.3
Earth Science
Riddle

2. 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

3. 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.

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. Water and Life Early Precambrian Late Precambrian Inhospitable No life
Covered with oceans
Cyanobacteria and other life forms

14. 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

15. Water and Life
Life on Earth is in every environment that contains water
Polar ice caps
Deep ocean vents