2. What is a System? A set of parts that work together Requires a source of energy to drive it Open parts can be either lost from or added to it Closed all the parts exist in precise amounts nothing can be lost or added essential ingredients must be recycled and reused

3. Is Earth Open or Closed?

4. Closed! All important ingredients (water, gases, nutrients) exist in limited amounts Ingredients must be recycled Energy source is the sun

5. So What? The essential ingredients can be used up or depleted If that happens, the system will no longer work

6. The Gaia Hypothesis British biochemist James Lovelock Created it in 1972 when he worked for NASA trying to detect life on Mars Earth should be seen as a single living organism Called it Gaia after the ancient Greek earth goddess Wrote book Gaia: A New Look at Life on Earth in 1979 Has continued to gather evidence since then

7. The Gaia Hypothesis cont’d. Planet Earth is the heart of an interconnected and unified living system regulates its own environment All life forms (from simplest to most complex) interact to produce best environment for own well-being and Earth as whole Gaia makes constant adjustments and interventions Species evolve to adjust to environmental challenges Great diversity of life forms

8. Is Gaia threatened? Lovelock says no Gaia is adaptable and resourceful Has adjusted to catastrophic events (like asteroid collisions) Has existed for much longer than humans Recent and short-term assaults by humans are not really a threat Greater threat is for humans because of how Gaia may react

9. How do Humans fit into Gaia? Read the excerpt from Lovelock’s book found on page 69 of the textbook