I just answered your other question and wrote all the definitions of the terms. I would say this is probably refering to Fusion because you are fusing together more nuclei into one nucleus. Fusion= bringing separate things into one entity.
The letter only has reflection symmetry, if you rotated it it would look the same.
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it will float back up because it's not dense enough to go down
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Formation. When the solar system settled into its current layout about 4.5 billion years ago, Earth formed when gravity pulled swirling gas and dust in to become the third planet from the Sun. Like its fellow terrestrial planets, Earth has a central core, a rocky mantle and a solid crust.