Life on Earth began roughly 3.5 to 4 billion years ago through chemical processes that created simple single-celled organisms in Earth's early oceans. Scientists believe non-living chemicals gradually organized into living cells through natural processes, though the exact steps are still being studied.

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Climate change is the long-term shift in Earth's average temperature and weather patterns, primarily caused by human activities that release greenhouse gases into the atmosphere. These gases trap heat from the sun and warm the planet, leading to changes in weather, sea levels, and ecosystems.

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Democracy is a system of government where power ultimately rests with the people, who exercise that power either directly or through elected representatives. It matters because it protects individual freedoms, ensures peaceful transfers of power, and allows citizens to have a voice in decisions that affect their lives.

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The scientific method is a step-by-step process scientists use to test ideas and discover facts about the world through observation and experimentation. It works because it removes personal bias and uses evidence to prove or disprove theories.

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Human history spans approximately 300,000 years, beginning with early humans in Africa and progressing through the development of language, agriculture, civilizations, and modern societies. Major milestones include the invention of writing, the rise of empires, and the scientific and industrial revolutions.

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