Chapter 8 - The Earth’s Formative Stages and the Archean Eon

1. Chapter 8 - The Earth’s Formative Stages and the Archean Eon Earth in Context: A little Astronomy Big Bang Formation of universe from golf ball sized energy Edwin Hubble and red shift Formation of Solar System Solar Nebula hypothesis Eight planets orbit in same direction Same plane (of the ecliptic) Rotate in same direction (not Venus)

2. Solar Nebula Origin Solar system formed from aftermath of supernova explosion “Heavy element” problem Stars don’t make elements heavier than iron (Fe) in “normal” fusion. .

3. Solar Nebula .

4. Formation Steps Giant gas ball Gravitational collapse towards center Protoplanet formation by accretion Fusion begins in sun with explosion 596 million tons H becomes 532 million tons of He Difference is energy “Blows” light elements away from inner solar system .

5. Planet Characteristics - Terrestraial Planets Terrestrial Planets Mercury - hot, small Venus - hot, 470°C (CO2), high atmospheric pressure (90 atmospheres), backwards spin Earth - just right, 15°C, 1 atm, large moon stabilizes spin Mars - -63°C, 0.1 atm Asteroid belt - broken planet?

6. Planet Characteristics - Jovian Planets Jovian Planets Large gaseous planets Jupiter, Saturn, Uranus, Neptune Planetoids: Pluto, Sedna, etc. Planet must have enough gravity to be spherical

7. Following Accretion, Earth Differentiates 4.53-4.56 billion years ago Earth is a random accumulation of space debris Partial melting (requires heat) Meteorite bombardment Gravitational collapse Radioactive decay (fission)

8. Differentiation Heavy material (iron, nickel) sinks Light material (oxygen, silicon) floats (scum) Core - partially molten Mantle Crust

9. Moon Formation Likely impact of Earth with a Mars-sized body early in solar system history Stabilizes earth’s spin Forms earth tides

10. Core Iron-nickel - two magnetic elements Liquid portion convecting and has slightly different spin rate Forms earth’s magnetic field Protects earth from solar wind Protects atmosphere from being “blown away” Mars?

11. Moon Formation Likely impact of Earth with a Mars-sized body early in solar system history Stabilizes earth’s spin Forms earth tides

12. The Archean Crust Komatiites - mafic volcanic rocks that form at high temperature Evidence of early plate tectonics? Mantled zircon 4.36 billion years old Early granitic rocks

13. The Primitive Atmosphere Today’s atmosphere 78% N2 21% O2 1% Ar 0.0036% CO2 Ancient atmosphere based on outgassing Nil O2 High CO2 Higher H2O than today (<4% today) SO2

14. Evidence for Little Oxygen Very few oxidized iron minerals Unoxidized Uranium mineral grains in sedimentary rocks Unoxidized pyrite in sedimentary rocks

15. Environmental Differences No (at least little) ozone (O3) No safety from UV radiation Organisms required protection from UV More acidic atmosphere and oceans Difficult to make calcite shells

16. Banded Iron Formation Alternating red chert and magnetite Source of iron in surface waters Weathering and alteration of older rock “Black Smokers” – divergent plate boundary undersea hot springs Cypress copper ore deposits Single most important iron ore mineral Ore: extracted for profit

17. Banded Iron Formation Outcrop

18. “Black Smoker”

19. The Primitive Ocean and the Hydrologic Cycle Early oceans are acidic Weathering of calcium (Ca), sodium (Na), and iron (Fe) neutralizes acidity Significant evidence that ocean salinity hasn’t changed much for at least 600 million years Stabilized by ocean floor circulation to 5 km?

20. The Primitive Ocean and Hydrothermal Circulation

21. Hydrologic Cycle

22. Origin of Precambrian Crust Hadean (Preston Cloud, UCSB) - no rocks Intense meteorite bombardment combined with plate tectonics and erosion destroys all early rocks Evidence from moon

23. Archean Eon 4.0 billion to 2.5 billion years ago High heat flow Abundant volcanism Few rocks remain Most Precambrian rocks found in continent interiors Africa has the most old rocks North America’s Canadian Shield (includes Greenland)

24. Archean Eon Continued 3.46 billion year old fossil soil is evidence of some land above sea-level Where are Archean rocks located? Shields and beneath platforms (combined = craton)

25. Exposed Precambrian Rocks

26. Craton, Shield and Platform

27. Precambrian Provinces of North America Craton growth accomplished by plate collisions Note arcuate shape of provinces

28. Earliest Plate Tectonics Supracrustal rocks: sedimentary rocks with no basement (floor removed) 3.8 billion year old Istaq Gneiss of Greenland and 4.04 billion year old Acasta Gneiss formed of tonalite (granitic rock) Earliest continents were small (<300 miles in diameter) and have grown by accretion where two continental plates collide forming a single continent that is “sutured” together by igneous rocks

29. 3.8 billion year old Amitsoq Gneiss

30. Granulites and Greenstones Archean rocks are grouped into two major associations Granulites - very high temperature metamorphosed granitic rocks Greenstones - metamorphosed volcanic rocks (green because of high iron) Pillow basalts Arcuate shaped belts formed in association with subducting plates (convergent plate boundary)

31. Steps in Greenstone Formation Ultramafic to mafic lavas ascended through rifts behind subduction zones to form the lowest layers of greenstone belts. Extrusion of increasingly more felsic (feldspar + silica) lavas and pyroclastics with deposition of sediments derived from erosion of adjacent uplands. Compression of above to form synclinal (down-warp fold) characteristic of greenstone belts.

32. Cross-Section of Greenstone Belt

33. The Origin of Life Basic building blocks of life at least partially from heavy meteorite, asteroid, and comet bombardment. Amino acids and other organic compounds Building block of proteins

34. Pulling Together the Pieces of Life Essential components of life: Protein-strings of amino acids. Building blocks of life and catalysts that assist in chemical reactions within organisms. Nucleic acids-large complex molecules found in nuclei of cells. RNA and DNA. DNA can replicate itself.

35. More Pulling Together the Pieces of Life Organic phosphorus compounds-transform light energy or chemical fuel into energy required for cell activities. A container-cell membrane to enclose cell’s components. Isolates cell’s chemistry from outside interference and manages the interaction between the cell’s contents and the outside world.

36. Simulating the Origin of Life Miller-Urey Experiment (1955) First synthesis of amino acids Simulated Earth’s early atmosphere containing methane (CH4), ammonia (NH4), hydrogen (H), and water vapor (H2O). Discharged electrical arc to simulate lightening in early atmosphere.

37. End Miller-Urey Experimental Apparatus Produced amino acids and other complex organic compounds. Works in the absence of oxygen (O2). Any other source of amino acids?

38. Where Did Life Begin? Primordial Ocean? Now doubtful since there would have been some O2 in shallow seawater. Midocean ridges? Total darkness (no photosynthesis), but lots of hot water with chemical nutrients.

39. Midocean Ridge Environment

40. Black Smokers

41. Tube Worms

42. Hyperthermophiles and Chemosynthesis Hyperthermophiles-high heat lovers. Bacteria live where water is over 100°C (!) in deep rock fissures. Erupt onto sea floor in clouds. Chemosynthesis-synthesize organic compounds from carbon dioxide (CO2) and by oxidizing hydrogen sulfide (H2S) or ammonia (NH4). No photosynthesis here. Shrimp-like arthropods, crabs, clams, and tube worms going up the food chain.

43. Archaea Domain Bacteria DNA distinct enough to include them in Archaea Domain.

44. Tubeworm Life How do these organisms live? Growth = 80 cm/yr! No mouth. No digestive tract. Symbiotic relationship w/ thermophilic microphilic microbes.

45. Life in Extremely Hostile Environments Many recent discoveries of life in extreme environments. Heat loving hyperthermophiles Microscopic life near poles at -113°C Microscopic life in hot (or cold) dry deserts Microscopic life under 3 km of solid rock Bacillus infernus (bacterium from hell) Lithotrophs (rock nourishment) Live off energy from hydrogen (H), iron (Fe), magnesium (Mg), and sulfur (S) Ancestors originate at surface and go down or the reverse? Both? Neither?

46. Looking for Life Homework: Please watch the NASA video on “Looking for Life”. Begin at about 43:31 into video. Will be on quiz.

47. Feeding Life Every organism requires energy and nutrients. Several methods of “feeding” or acquiring energy. Fermentors – ferment pre-existing food Sugar + yeast activity ----- carbon dioxide + alcohol + energy Autotrophs – manufacture their own food sulfur dioxide (SO2) + hydrogen sulfide (H2S)  energy Photoautotrophs – manufacture their own food using light carbon dioxide (CO2) + water + light  sugar + energy + oxygen

48. Feeding Life II Heterotrophs - can’t make own food. Scavenge nutrients from environment. Ate neighbors. Animals. Anaerobic organisms - O2 is lethal to these organisms. Slowly adapted to growing O2 by developing oxygen-mediating enzymes that permit peaceful co-existence with O2. Botulism is an example. Aerobic organisms - organisms that require O2 to live. Chemically more efficient, hence more successful.

49. Prokaryotes and Eukaryotes Earliest organisms were likely prokaryote bacteria. Prokaryotes Genetic material distributed throughout cell. Reproduce asexually. Fission. Clone. Cyanobacteria (blue-green algae). 1 - 10 micron in size. Eukaryotes Genetic material contained in cell nucleus. Organelles that perform specialized functions. Reproduce sexually by mixing genetic material with another organism. 10 - 100 micron in size.

50. Eukaryotes Evolution Organelles developed as independent microorganisms that moved into other cells and established symbiotic relationship with host. One cell envelops but does not digest another. Symbiotic relationship. Reproduce together. Become organelles. Eventually lose ability to function independently.