Ch. 22 Sec. 3

1. Ch. 22 Sec. 3 Formation of the Atmosphere & Oceans

2. The formation of Earth’s oceans and atmosphere provided a hospitable environment for life to begin. Review Vocabulary ultraviolet radiation: high-energy rays from the Sun that can damage living organisms

3. I. Formation of the Atmosphere • Asteroids, meteors, and other objects collided with Earth • 1. Water vaporized on impact, forming a haze around the planet • 2. Hydrogen & Helium escaped into space • 3. Ammonia & Methane broken down by UV rays

4. B. Outgassing • Volcanic eruptions release gases • a. Water vapor • b. Carbon Dioxide (CO2) • c. Nitrogen

5. II. Oxygen in the Atmosphere There were only negligible amounts of free oxygen in Earth’s atmosphere until the early Proterozoic.

6. A. First oxygen producers • Fossils preserved in rocks in Australia and South Africa that are about 3.5 billion years old appear to be traces of tiny, threadlike organisms called cyanobacteria. • a. Photosynthesis • b. Oxygen waste product • c. Changed atmosphere at the end of the Archaen

7. 2. By the early Proterozoic, large, coral reef-like mounds of cyanobacteria called stromatolitesdominated the shallow oceans that at that time covered most of Earth’s continents.

8. B. Evidence in rocks 1. The absence of iron oxides in rocks of the late Archean indicates that there was no free oxygen gas in the atmosphere at that time.

9. 2. Banded-iron formations a. Early Proterozoic b. alternating bands of iron oxide and chert, an iron-poor sedimentary rock.

10. 3. Red beds a. Sedimentary rock deposit b. 1.8 by old c. Evidence that oxygen existed in the Proterozoic

11. C. Importance of oxygen • Animals require it for respiration • Provides protection from harmful ultraviolet radiation (UV) from the Sun • a. ozone layer began to develop • b. providing an environment where new life-forms could develop

12. Besides being necessary for animal life, why else is the presence of oxygen in the atmosphere important? Oxygen forms ozone in the atmosphere, which provides protection from ultraviolet radiation from the Sun.

13. III. Formation of the Oceans The water that filled the oceans probably originated from the two major sources that provided water in Earth’s atmosphere: volcanic outgassing and asteroids, comets, and other objects that bombarded Earth’s surface. As Earth cooled, the water vapor in the atmosphere condensed to form liquid water.

14. A. Rain • Filled the low-lying basins • Dissolved Earth surface minerals • Run-off, rivers, groundwater • a. Salty oceans • b. Uniformitarianism

15. B. Water and life The Precambrian began with an environment inhospitable to life. When it ended, much of Earth was covered with oceans that were teeming with tiny cyanobacteria and other life-forms. Life as it exists on Earth today cannot survive without liquid water.

16. The search for life elsewhere in the solar system and universe • today is centered on the search for water. • Ceres (asteroid) • Mars • Moons of Jupiter & Saturn

17. The formation of Earth’s oceans and atmosphere provided a hospitable environment for life to begin. • Earth’s atmosphere and oceans began forming early in Earth’s history. • Oxygen gas began to accumulate in the Proterozoic by photosynthesizing cyanobacteria.

18. Evidence for atmospheric oxygen can be found in rocks. • The water that filled Earth’s oceans most likely came from two major sources.

19. What is the probable source of water in Earth’s atmosphere and oceans? The water probably came from asteroids, comets, and other space objects, as well as from volcanic outgassing.