Introduction

Although the world's attention has recently been captured by stunning pictures of comet Hale-Bopp and by the discovery of microbe-like structures within a Martian meteorite, recent Hollywood films suggest our fascination with such objects comes mostly from the fear that they might destroy us. However, the real "impact" these objects have had in our lives ^__ as part of God's work in constructing the Earth and its life-supporting ocean - has tended to escape our notice.

According to Genesis 1:2, the Earth in its infancy was covered by water: "darkness was over the surface to the deep; and the spirit of God was moving over the surface of the waters." Likewise, there is widespread scientific agreement that the newborn Earth was indeed covered by water (and darkly so). Planetary scientists generally believe that the Earth formed through an accretion process from a rotating disk of gas and dust around our Sun which gravitationally collapsed. Dust particles which condensed within this cloud began to form larger meteoritic-type bodies, called planetesimals, through cohesion and collisional accumulation. Continued collision and coalescence of these bodies produced embryonic planets, which in turn grew into the Earth and the other planets we see today.
 

Evidence that Earth was essentially hammered together piece-by-piece through such a process includes the clearly-cratered surfaces of the Moon, Mars and Mercury, and the various axial tilts and chemical compositions found among the planets.¹ Fortunately, the continuation of this process on a small scale has allowed us to examine the very mortar of our planet - meteorites. Scientists have discovered that a careful mixing and pounding together of this mortar not only produced the Earth, but also our oceans and atmosphere. After all, "This is what God the Lord says ^__ he who created the heavens and stretched them out, who pounded out² the earth and all that comes out of it" (Isaiah 42:5).
 

Composition and Alteration of Meteorites

Compositional analyses of meteorites have shown that some of them contain significant amounts of water, especially carbonaceous chondrites, a type of stony meteorite. Type 1 carbonaceous chondrites (commonly known as CI chondrites) may contain up to 20% of H₂O in the form of hydrous minerals known as phyllosilicates.^3-4 Because these chondrites have elemental abundances similar to those of the Sun, they are recognized as the most primitive type of material we have surviving from the early solar system.⁵ Carbonaceous chondrites also have atomic weight compositions (i.e., ratios of the various isotopes) of carbon, nitrogen, hydrogen, and inert gases similar to that of the outer shell or crust of the Earth.⁶ Study of the rock-forming elemental abundances, water and other volatile contents of these meteorites (along with other chondritic types) can also be related closely to the bulk composition of the Earth.^7-9
 

Evidence that the water in meteorites we recover is indigenous, rather than due to terrestrial contamination, includes measurements of their isotopes plus abundant signs of their early aqueous alteration. The presence in these meteorites of water-bearing silicate mineral veins, and veins of water-precipitated minerals such as sulphates and carbonates, indicate that liquid water once circulated through the meteorite's parent body.^10-11 Measurements of the ratios of magnesium and chromium isotopes within carbonate veins in CI chondrites have also shown that this aqueous activity sometimes occurred very early, just after the first solids formed from the solar nebula.¹² Minerals within the meteorites may be further altered hydrothermally by shock deformation from impact.^13-14
 

Unfortunately impact effects, melting, and subsequent alteration on Earth (or even high within our atmosphere) limit some of the usefulness of this information, making it difficult to determine whether a meteorite has come from a comet or from some other body such as an asteroid. Consequently, scientists are looking forward to the return of NASA's Stardust spacecraft, which in 2006 is expected to bring back from the comet Wilt-2 some pristine nebular dust believed to be of chondritic composition.¹⁵
 

Formation of the Early Atmosphere and a World Ocean

However, this alteration of meteoritic material has benefitted us as well. Experiments in which stony meteorites have been subjected to such extreme shock pressures or heating as would occur from their impact with Earth demonstrate that they would have lost their water and other volatiles such as CO₂. This dehydration or outgassing of the parent rock begins to occur when the impact velocity exceeds about 2 km/sec, with complete dehydration for speeds greater than 4 km/sec.^16-18 Planetesimals falling onto objects like the Earth would have achieved velocities sufficient to totally devolatize the incident bodies by the time the Earth had grown to about 27% of its present size.¹⁹ Consequently, a primordial atmosphere composed mostly of water vapor and lesser amounts of CO₂ was generated.

Studies which model the more complex effects of the shock devolatization of chondrites have shown that large impacts on the one hand, or the blanketing effect of an impact-induced atmosphere on the other, can increase the surface temperature of the accreting Earth to the point where a magma ocean is formed.^20-23 Any surviving volatiles in the planetesimals would then dissolve in the magma. The magma layer would allow iron and silicate separation to occur, with the iron subsequently sinking to form the Earth's core. The magma ocean in turn controls the amount of H₂O in the atmosphere since water can easily be dissolved into the silica-rich magma or degassed from it, depending on the atmospheric pressure. This has profound implications. Even if the Earth's atmosphere was once lost into space from a large impact during the accretion process, water vapor could be outgassed from the remaining magma and replenish it.²⁴

As the accretion rate slowed and the radius of the Earth approached its present value, the interior heat of the Earth eventually decreased, and solar radiation became the main heat source for the atmosphere. Since the solar radiation could not readily penetrate the dense, opaque atmosphere, the lower atmosphere began to cool and the water in the atmosphere condensed into a liquid.^25-26 With careful nurturing and "swaddling" of the Earth by a thick blanket of atmosphere, a world ocean was formed.
 

Our Unique Ocean: an Example of Fine-Tuning

Since the early accretion-history of our neighboring planets Venus and Mars should have been similar to the Earth's, we can infer from their present lack of oceans that a set of fine-tuned conditions is necessary for water to condense and remain as an ocean.
 

Venus, for instance, has about the same size and density as Earth and was formed at a somewhat comparable distance from the Sun. As a result, Venus is assumed to have formed from planetesimals containing H₂O in amounts similar to those that formed the Earth. In fact, the present ratio of deuterium-to-hydrogen on Venus supports the idea that the planet once had an initial mass of atmospheric water that was equal to the Earth's.²⁷ Nevertheless, the early temperature conditions on Venus, a good deal warmer than on Earth, were not conducive to condensing an ocean on its surface.²⁸
 

Mars, on the other hand, has a landscape shaped by liquid water - even though the planet is 50% further from the Sun and has only a tenth of Earth's mass. However, the bulk of the water (except for ice at the poles and possibly some beneath its surface), is believed to have dissociated into the lighter molecules of hydrogen and oxygen which then escaped into space.^29-30

To form and maintain an ocean, the Earth had just the right balance of solar energy, internally derived heat, and heat created from the impact and accretion process. The amount of water in the atmosphere was held at just the right amount as God "weighed out the waters by measure" (Job 28:25). The Earth both battled against and benefited from the erosive impacts of large planetesimals, and as a result kept the necessary gravitational size to retain enough water rather than losing it all to space. The magma "mantle" layer and the atmosphere also worked in harmony to keep just the right balance of water and other volatiles such as CO₂. Even today, processes within the mantle, chemical alteration of the oceanic crust beneath the seas, and weathering of our continents have worked to maintain a life-sustaining balance of water in the oceans and atmosphere.^31-33 It has also been suggested that any water loss to space may have been made up by continued input of water from meteoritic or comet material.³⁴
 

Continents: The Earth Beneath Our Feet

Ultimately, the water of the ocean which was measured "in the palm of His hand" (Isaiah 40:12) was used in the formation of the earth beneath our feet. When the Earth had cooled and condensed an ocean of water, unstable rock crusts were also formed atop the magma ocean, and these lay beneath the sea. Subsequently, convection currents within the underlying mantle moved portions of this crust (as plates) relative to one another, so that new oceanic crust formed where plates were spreading apart, just as today. As for the land we stand on - the continental crust - it formed by hydrous processes within the magma at places where water-bearing oceanic crusts sink into the magma or collide such that portions get carried down beneath another.^35-36
 

The resulting crust is unique among the known planets. It has a composition rich in SiO₂, since H₂O tends to make silica-rich magmas, in contrast with CO₂ which makes silica-poor magmas (as we find on Mars).³⁷ Since this silica-rich continental crust is less dense than the oceanic crust, it is lifted up and rises to the top. Just as commanded in Genesis, "let the dry land appear." In addition, the distribution of our continents suggests that following the formation of continental crust, God also "spread out the earth above the waters" (Psalms 136:6).

With all of this in mind, it should not escape our notice that - according to 2 Peter 3:5 and Psalm 24:2, respectively - "the earth was formed out of water and by water" and that "He has founded it upon the seas."

References:

1. Stuart Ross Taylor, "Early Accretional History of the Earth and the Moon-Forming Event," Lithos 30 (1993) pp. 207-221.
 

2. James Strong, "Hebrew and Aramaic Dictionary of the Old Testament," in The New Strong's Exhaustive Concordance of the Bible, (Nashville: Thomas Nelson, 1996), p. 135; see the word raqa' (no. 7554).
 

3. H. B. Wiik, "The Chemical Composition of Some Stony Meteorites," Geochemica et Cosmochimica 9 (1956), pp. 279-289.
 

4. Kazushige Tomeoka, "Phyllosilicate Veins in a CI Meteorite: Evidence for Aqueous Alteration on the Parent Body," Nature 345 (1990), pp. 138-140.
 

5. D. S. Burnet et al, "A Test of the Smoothness of the Elemental Abundances of Carbonaceous Chondrites," Geochim. cosmochim. Acta 53 (1989), pp. 471-481.
 

6. E. M. Galimov, L. A. Bannikova, and V. L. Barsukov, "The Material That Formed the Outer Shell of the Earth," Geochemistry International 19-2 (1982), pp. 473-489.
 

7. E. M. Galimov, L. A. Bannikova, and V. L. Barsukov, pp. 473-489.
 

8. Marc Jovoy, "The Birth of the Earth's Atmosphere: the Behaviour and Fate of Its Major Elements," Chemical Geology 147 (1998), pp. 11-25.
 

9. Constance M. Bertka and Yingwei Fei, "Implications of Mars Pathfinder Data for the Accretion History of the Terrestrial Planets," Science 281 (1998), pp. 1838-1840.
 

10. Kazushige Tomeoka, "Phyllosilicate Veins in a CI Meteorite: Evidence for Aqueous Alteration on the Parent Body," Nature 345 (1990), pp. 138-140.
 

11. Magnus Endress, Ernst Zinner, and Adolf Bischoff, "Early Aqueous Activity on Primitive Meteorite Parent Bodies," Nature 379 (1996), pp. 701-703.
 

12. Magnus Endress, Ernst Zinner, and Adolf Bischoff, pp. 701-703.
 

13. Kazushige Tomeoka, pp. 138-140.
 

14. J. R. Achworth and R. Hutchison, "Water in Non-Carbona-ceous Stony Meteorites," Nature 256 (1975), p. 714.
 

15. Laura Garwin, "Comet Leaves a Trail in the Air,"Nature 392 (1998), pp. 754-755.
 

16. Manfred A. Lange, "Impact Vaporization of Water in Hydrous Minerals," Eos 60 (1979), p. 308.
 

17. M. A. Lange and T. J. Ahrens, "The Evolution of the Impact Generated Atmosphere," Icarus 51 (1982), pp. 96-120.
 

18. James A. Tyburczy, Benjamin Frisch, and Thomas J. Ahrens, "Shock-Induced Volatile Loss from a Carbonaceous Chondrite: Implications for Planetary Accretion," Earth and Planetary Science Letters 80 (1986), pp. 201-207.
 

19. James A. Tyburczy, Benjamin Frisch, and Thomas J. Ahrens, pp. 201-207.
 

20. Yutaka Abe, "Physical State of the Very Early Earth," Lithos 30 (1993), pp. 223-235.
 

21. Yutaka Abe and Takafumi Matsui, "The Formation of an Impact-Generated H₂O Atmosphere and Its Implications for the Early Thermal History of the Earth," J. Geophys. Res. 90 (1985), pp. C545-C559.
 

22. Yutaka Abe and Takafumi Matsui, "Early Evolution of the Earth: Accretion, Atmosphere Formation, and Thermal History," J. Geophys. Res. 91 (1986), pp. E291-E302.
 

23. Takafumi Matsui and Yutaka Abe, "Impact-Induced Atmospheres and Oceans on Earth and Venus," Nature 322 (1986), pp. 527-528.
 

24. Yutaka Abe and Takafumi Matsui, "Early Evolution of the Earth: Accretion, Atmosphere Formation, and Thermal History," pp. E291-E302.
 

25. Yutaka Abe and Takafumi Matsui, "The Formation of an Impact-Generated H₂O Atmosphere and Its Implications for the Early Thermal History of the Earth," pp. C545-C559.
 

26. Takafumi Matsui and Yutaka Abe, pp. 527-528.
 

27. T.M. Donahue, J. H. Hoffman, R. R. Hodges, Jr., and A. Watson, "Venus Was Wet; a Measurement of the Ratio of Deuterium to Hydrogen," Science 216 (1982), pp. 630-633.
 

28. Takafumi Matsui and Yutaka Abe, pp. 527-528.
 

29. Vladimir A. Krasnopolsky, Michael J. Mumma, and G. Randall Gladstone, "Detection of Atomic Deuterium in the Upper Atmosphere of Mars," Science 280 (1998), pp. 1576-1580.
 

30. James Farquhar, Mark H. Thiemens, and Teresa Jackson, "Amosphere-Surface Interactions on Mars: ¹⁷O Measurements of Carbonate from ALH 84001," Science 280 (1998), pp. 1580-1582.
 

31. J. R. Lawrence and M. Taviani, "Extreme Hydrogen, Oxygen and Carbon Isotope Anomalies in the Pore Waters and Carbonates of the Sediments and Basalts from the Norwegian Sea: Methane and Hydrogen from the Mantle?," Geochim. Cosmochim. Acta 52 (1988), pp. 2077-2083.
 

32. N. C. Flemming and D. G. Roberts, "Tectono-Eustatic Changes in Sea Level and Seafloor Spreading," Nature 243 (1973), pp. 19-22.
 

33. Kiyoshi Kuramoto, "Accretion, Core Formation, H and C Evolution of the Earth and Mars," Physics of the Earth and Planetary Interiors 100 (1997), pp. 3-20.
 

34. Richard A. Kerr, "Spots Confirmed, Tiny Comets Spurned" Science 276 (1997), pp. 1333-1334.
 

35. Kiyoshi Kuramoto, pp. 5-6.
 

36. K. C. Condie, Plate Tectonics and Crustal Evolution, (Oxford: Pergamon Press, 1989), pp 342-345.
 

37. Kiyoshi Kuramoto, p. 5.