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Earth


Contents

The Beginning
Geological and Biological Records
Internal Structures
Continental Drift
Rocks, Minerals, and Gemstones
Atmosphere
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 reaches a diameter of 500 km. Figure 09-02 shows a half-sized Earth. It was a heavily cratered world
Earth, Embryo Earth, Half-sized Earth, Primitive 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 09-03 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 09-03 Earth, Primitive, 4540 My ago
[view large image]

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