Life was anaerobic, meaning that it did not need oxygen to live and grow. When life first arose (likely more than four billion years ago), there was no free oxygen in the atmosphere at all. About 21% of Earth’s atmosphere is oxygen, and most of the rest is nitrogen. That buildup makes a significant impact on our climate, but overall, carbon dioxide still comprises a small percentage of the atmosphere, less than 0.05%. Atmospheric carbon dioxide levels have increased by more than 40% since the Industrial Revolution. That accord aims to curb global warming by limiting the greenhouse gases, notably carbon dioxide, that human activity adds to the atmosphere. As the evidence pointing to human-produced greenhouse gases as the cause of ongoing and future global climate change has mounted, so too has public attention to this threat - most recently manifest in concern over whether the United States will pull out of the Paris climate accord. The make-up of Earth’s atmosphere, once the domain of Earth science textbooks, has become an increasingly “hot” news topic in recent decades. Information on controversies in the public arena relating to evolution.Alignment with the Next Generation Science Standards.The big issues – Pacing, diversity, complexity, and trends.Macroevolution – Evolution above the species level.Microevolution – Evolution within a population.Mechanisms: the processes of evolution – Selection, mutation, migration, and more.The history of life: looking at the patterns – Change over time and shared ancestors.An introduction to evolution: what is evolution and how does it work?.
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