SCIENCE Use the vocabulary words from "Read It" to complete the following sentences.
Approximately 2.7 - 2.2 billion years ago, (4) released oxygen through photosynthesis, (5) , which protects our planet and gives us air to breathe. Unfortunately, over time, humans have contributed to (6) . One reason for this is the burning of (7) , like oil and coal. Doing so releases (8) like carbon dioxide and methane into the atmosphere, which trap heat from the sun. This is the greenhouse effect, which gradually warms the planet.