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Earth was created around 4.5 billion years ago and life began not long after. Primitive life likely possessed the elemen..
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Geological periods is a study guide that cites the different geological periods on Earth's timeline. Each has a brief ov..
The water cycle (also referred to as the hydrological cycle) is a system of continuous transfer of water from the air, s..
Humans are capable of only one mode of reproduction, i.e. sexual reproduction. Haploid sex cells (gametes) are produced ..