GEF

Unit 4   |  The Global Ecosystem 90 As you study sustainability, keep these facts in mind: ■■ The Earth formed about 4.5 billion years ago. ■■ Scientists estimate the first life forms emerged about 3.9 billion years ago. ■■ The earliest form of modern humans, Homo sapiens, evolved in the past 200,000 years. To put this time span in perspective, spread your arms out wide. All geologic time is represented by the span from a fingertip from one hand to the other. If you filed a nail on your right hand, the resulting nail dust is approximately the length of time humans have been on Earth. Knowing this helps us put our human place on Earth in perspective. Human life, along with the rapid growth of modern civilization, has developed in a geological blink of an eye. WATCH & LEARN http://bit.ly/2uw5uts Watch the video and respond to the questions below. 1. What does it mean to be a system? 2. Write a paragraph or draw a picture that illustrates how the planet Earth is a system. video: The Earth as a System