ORIGIN OF EARTH--DIFFERENTIATION MULTIPLE WORKING HYPOTHESIS

I. Density Differences

1. Heavy mineral and elements sunk to center, Light element floated to surface

2. Outer liquid core, inner solid core

-variation in Heat and Pressure

II. Planetessimal Accretion Hypothesis (Golberg--The Sea Vol. 5)

 

 

 

 

1. Earth accreted slowly and was cool orginially (solid inner core)--Heavier elements (minerals) greater gravitational attraction

2. Impact increase--heat increase and molton outer core forms-impacts per unit area increases

3. Surface area increases resulting in decrease of heat due to impacts--mantle accreted cold

4. formation of H20 occurs approximately at the same time as the mantle

EVOLUTION OF ATMOSPHERE AND HYDROSPHERE

RELATIVE ABUNDANCE OF ELEMENTS (WT)

Crust             Whole Earth                 Atmosphere                      Ocean

O 46.60             Fe 36.9                         N2 78.1                              H2O

Si 27.72             O 29.3                          O2 20.9                              Cl 55.05

Al 8.13            Si 14.9                         An .93                              Na 30.68

Fe 5.00            Mg 6.73                         CO2                                     SO4 7.68

Ca 3.63            Ni 2.94                         Ne                                     Mg 3.67

Na 2.83            S .73                                 He                                      Ca 1.16

K 2.59            Ca 2.99                         CH4                                     K 1.10

Mg                      Al 3.01                         Kr                                     HC03 .41

                            Na .90                                  03

                            K .29                                 Xe

Evolution of Atmosphere and Hydrosphere

(Water Planet 70.8% surface)

139,400,000 square miles

 

Schools

I. H2O, CH4, NH3--1'st stage of Atmospheric and Hydrosphere evolution

increse in O2

NH3 + O2-------H2O = N2 **outer planets

[0] + O2 ----03

CH4 + 2O2-------CO2 + 2H2O

 

II. Early Atmosphere

H2O, CO2, CO, N2, SO2, HCL, H2

Rubey and Abelson

III. Water (Origin)

1. small range in Temperature

2. Volume How it forms in Large quantities

3. How did condition remain favorable for long period of geologic time

 

 

 

IV. Origin of Water

1. Rubery, W.W. "Theory of Excess Volatiles"

2. Excess Volatiles--Volatile (gases) material too abundant in present atmosphere, hydrosphere, biosphere and in ancient sediments to be explained by rock weathering alone

Excess Volatiles (1020) grams

H2O      Ca3CO2        Cl                 Ni                 Si

Present Atmosphere, Hydrosphere, bios. 14,6000

Buried in Sedimentary Rocks 2,100

__________

    16,700

Supplied by rock weathering of Crystalline rocks 130

Excess volatile unaccounted for by rock weathering 16,570

Solutions:

(1) origin of H2O, etc from Volcanoes, fumeroles, hot Springs

(2)If took 0.8% of gases from above that is all that is needed to account for volume in oceans

 

ORIGIN OF HYDROSPHERE AND ATMOSPHERE

 

EVIDENCE FROM METEORITES

Stony Meteorites

O=   m                     Mantle Volume =     1027 cm3

        v                     Mantle Mass             4.5 x 1027 gr

                                    = 0.031% Mass lost to produce oceans

Stony meteorites closest comparison to mantle contain 0.5% H2O

.05%     =     16.1--more than enough

.031%

 

QUICK SOAKS VS. SLOW SOAKS

 

 

 

 

Slow Soaks (favored)

1. gradual accumulation

2. major increase in Ocean Basins throughout geologic time in depth

3. continents increasing in volume

4. 5% salinity constant (at least for last 600 million years) 34.7%

 

 

 

 

 

ATMOSPHERIC AND HYDROSPHERIC EVOLUTION ON THE PRIMITIVE EARTH (P. CLOUD)

CONCLUSION:

1. answers lie in rock record

2. we must have a secondary atmosphere

a. depletion of noble gases

b. outer planets

3. Atmosphere and Hydros arose from interior of Earth

4. Primitive atmosphere

O2 N2, CO2 and H2

5. Atmosphere and Hydrosphere

No older than 4.5 x 109 years

6. Oldest Earth Rocks 3.0-3.8 billion years

7. Oldest Rock Metasedimentary water laid sediments, Atmosphere weathering and erosion

8. NO O2 prior to about 1.8-20 billion year

a. detrital uranite and pyrite

b. bedded chemical Silicates (cherts)

9. Little NH3-rarity of Limestones and dolomites in oldest sedimentary rocks

NH3 would raise PH and favor precipitation of carbonate rocks and rarity of chert

10. No CH4--NO Oxygen, CH4 would disassociated resulting in Carbon deposits

11. Sedimentary record supports

Rubey's H2O, CO2, CO, N2, SO2, HCL for Atmosphere from about 3.5 billion years to present

12. Presence or Absense of Moon "Lunar capture"

Clues in rock record-Tides and Tidal Amplitude

a. Stromatolites--green Algae, X-bedding and dessication cracks

Stromatolites indicative of tidal flat deposition

 

 

 

Form today in intertidal area (Bermuda, W. Australia)

Associated with OOlites and Breccias

b. P-C and Paleozoic Stromatolites have greater heights than do more recent forms

*2.5-6 months

Belt series--Montana

15 ft thick

c. Greater intertidal ranges suggest moon closer to earth about 2 billion years ago

3 billion years Ago--moon present (X beds, ripples, mud cracks)

d. Lunar Capture, 3.5 billion years, Therman event reset radiometric clocks

 

SUMMARY

FORMATION AND EVOLUTION OF EARTH

I. First 600-800 million years (Hadean Interval)

a. indirectly recorded

1. events on moon

2. comparative planetology

3. geochemical clues from meteorites and younger terrestial rocks

4. computer modeling

b. Earth began to accrete from solar nebula as solid body about 4.6 b.y ago

c. Within 100 m.y or less it was essentially complete

d. Gravitational energy plus heat from compression and short lived (half live) radioactive isotopes elevated temperatures to or above the melting point of iron up to shallow depths

e. Fe trickled downward through silicate much to create Earth's bilayered iron core and concentric shells of silicate mantle

f. In response to requirements of conservation of angular momentum Earth's rotation accelerated.

g. Dynamo motions in the molten outer core resulted in a magnetic field and a radiation-shielding magnetosphere.

II. During next few hundred million years the planetessimal in fall that created the initial earth tapered off to a rate of only 20X the present

III. Earth cooled to form solid crust about 4 billion years ago

Some evidence suggests an increase of meteoritic bombardment between 4 and 3.8 billion years ago

IV. This type of infall may have veneered the Earth's surface with large quantities of Carbon rich debris from asteroid belt and volatile-rich comets (Gravitational affects of massive Jupiter may be involved)

V. Carbon rich deposits, volatile comets plus outgassing of occluded volatiles from Earth's mantle probably accound for initial Atmosphere and Hydrosphere.

VI. May also be source of Carbonaceous macromolecules--first microbial creature arose

a. First life anaerobic because No source for corrosive O2

b. also heterotrophic because synthesis of nutrients is biochemically advanced

c. microbial-because diffusion in and out of small spheroid is simplest energy efficient metabolic system

d. self catalysis and radiant solar energy joint with more esoteric processes as prohable driving forces for chemical selection to life

VII. Initial Atmosphere from which present Atmosphere evolved and beneath which life evolved was anoxic or neutral (Traces of free O2) consisting of CO2, H2O, N2 and reduced gases

VIII. End of Hardean time--3.8 billion years ago

a. Atmosphere and Hydrosphere present

b. Microbial life in seas beneath anoxie atmosphere