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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] |
spherical shape when it 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 | Figure 09-02 Earth, Half-sized, 4550 My ago | Figure 09-03a Earth, Primitive, 4540 My ago |
form only 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 |