Home Page Overview Site Map Index Appendix Illustration About Contact Update FAQ



The Beginning
Geological and Biological Records
Internal Structures
Continental Drift
Rocks, Minerals, and Gemstones
Weather and Climate
Habitable Zone
Extra-Terrestrial Intelligence
Starry Night
The End

The Beginning

Beginning The Solar system started with the collapse of a cloud of interstellar gas and dust. Gravity caused the cloud to fragment and condense into ball of heated gas that eventually became the Sun. Meanwhile, whirling disks around the nascent star gave birth to the planets. About 4.5672 billion years ago bits of dust around the growing Sun started sticking together to form small, inch-long clumps (reproducible in the laboratories). The next step was amalgamation of the small bits into mile-wide objects call planetesimals. Figure 09-00 illustrates the successive stages in the earlier growth of planet Earth.

Figure 09-00 The Beginning [view large image]

The three illustrations below provides a reasonable conjecture on further development of the Earth 4.5 billion years ago. Figure 09-01 shows a larger planetesimal attracting the smaller ones from the surrounding dust clouds. This nondescript rock will have a more spherical shape when it
Earth, Embryo Earth, Half-sized Earth, Primitive reaches a diameter of 500 km. Figure 09-02 shows a half-sized Earth. It was a heavily cratered world covered with magma produced by planetesimal impacts. The new world was beginning to acquire a thin atmosphere. The cloud patterns are more belt-like because of the faster rotation. Figure 09-03a shows a primitive Earth in the process of solidification.

Figure 09-01 Earth, Embryo, 4560 My ago
[view large image]

Figure 09-02 Earth, Half-sized, 4550 My ago
[view large image]

Figure 09-03a Earth, Primitive, 4540 My ago
[view large image]

Hydrogen and oxygen are the 1st and 3rd most abundant elements in the Universe. They have a proclivity to form water whenever there is an opportunity. Thus, water should be rather common everywhere in the Universe. Yet it seems to be very rare because it exists in this form only
Earth, Water Earth-Moon Collision between 0 - 100 oC turning into ice or vapor beyond this range. This comfortable region is called "Habitable Zone" in present era of the Solar system. It was the "Snow Line" at the time of formation. This strip separated the dry and wet planetesimals. The "Water History" of the Earth started at this point (Figure 09-03b). The following is a summary for the rest of the "Oceans from the Skies" narration published in the March 2015 issue of Scientific American plus a latest news about the formation of the Moon.

Figure 09-03b Earth, Water from sky [view large image]

Figure 09-03c Earth-Moon Collision [view large image]

  1. The Proto-Earth was formed from a mixture of dry and wet planetesimals. Most of the water turned into hydrated minerals and sank down to the mantle with some residuals remained on the surface.

  2. Collision with a big asteroid evaporated most of the water. This event created the Earth-Moon system. The latest computer simulation in 2015 shows that the proto-Moon and proto-Earth were "sisters" with similar composition. Based on their common origins at similar orbital distance from the Sun, it is estimated that the chance for collision would be 20% to 40% (Figure 09-03c).

  3. The re-development of the water content then becomes an issue to be explained :
  4. Whatever the mechanism of water delivery, the Earth has steadily acquired water to covered 2/3 of its surface today. Actually, the total amount of water in the ocean is not that extra-ordinary as it constitutes only about 0.02% of the mass of Earth with equal amount in the form of hydrated rocks and minerals locked up in the mantle.
It could be that water simply rained down from the sky regardless of whether its carrier is comet, asteroid, dwarf planet, or solar wind, etc ... It is not possible to distinguish which one contributed more.

Go to Next Section
 or to Top of Page to Select
 or to Main Menu