Earth as a Living System
In his award-winning documentary film about climate change, An Inconvenient Truth, Al Gore's characterization of Earth as having a fever is a clever metaphor of global warming. Is there more to this statement than meets the eye? What does it mean to be a living thing? How far can a definition of "living" be extended? Read on and judge for yourself!
BASIC
Do living things have common features? Have you ever considered how Earth might be characterized as "alive"? Use the web to identify those qualities that define a living thing and then explain, in your eFolio, how each characteristic might apply to Earth. When you are done, check out these resources and discover the world of James Lovelock and his Gaia Hypothesis. Give us your reaction to these ideas. For more information about James Lovelock, his theory of Gaia and his thoughts on global warming, listen to this interview.
James Lovelock named his theory of Earth as a self-regulating living system “Gaia” at the suggestion of his friend and neighbor, Nobel Prize winner James Golding, a novelist most famous for his work, Lord of the Flies. Gaia is a Greek goddess who personifies Earth, and who, according to Greek mythology, was the first god to appear after Chaos, the primeval state of existence.
In response to critics who have pointed out that Earth cannot be considered as “living” because of its inability to reproduce and pass on genetic material to later generations, the noted scientist and futurologist, Carl Sagan, observed that the space probes since 1959 have “the character of a planet going to seed.” Indeed, human interest in space exploration and colonization of other planets and the concept of “terraforming” provides an interesting interpretation of this issue.
GRAB YOUR POINTS!
1. Log into eFolio. The link below will place your work into the eFolio and give you the Mini Survey.
GOING BEYOND
One of the characteristics of living things that you should have identified in the first level of this challenge is homeostasis, the ability of an organism to maintain a stable, constant internal environment. The human body is an obvious example of a homeostatic system, because of its ability to maintain a constant internal temperature and stable chemical levels.
James Lovelock has suggested that Earth is a homeostatic system. Life on Earth (i.e. its biota) provides a feedback system that is automatic and unconscious and that leads to a stabilization of global temperature and chemical composition of the atmosphere and oceans. He has noted that:
- The global surface temperature of the Earth has remained constant, despite an increase in the energy provided by the Sun.
Since life started on Earth, the energy provided by the Sun has increased by 25% to 30%, yet the surface temperature of the planet has remained remarkably constant when measured on a global scale.
- Atmospheric composition remains constant, even though it should be unstable.
The Earth's atmosphere currently consists of 79% nitrogen, 20.7% oxygen and 0.03% carbon dioxide. Oxygen is the second most reactive element after fluorine, and should combine with gases and minerals of the Earth's atmosphere and crust. Traces of methane (at an amount of 100,000 tons produced per annum), should not exist, as methane is combustible in an oxygen atmosphere. This composition should be unstable, and its stability can only have been maintained with removal or production by living organisms.
- Ocean salinity is constant.
Ocean salinity has been constant at about 3.4% for a very long time. Salinity stability is important as most cells require a rather constant salinity degree and do not tolerate values much above 5%.
In order to demonstrate this idea, Lovelock created a simplified (really simplified!) mathematical model of the world (yes, the entire world!) called DaisyWorld. You can read about DaisyWorld here.
In this exploration, we are going to work with a version of DaisyWorld that supports only one daisy specie, a white one that grows on an otherwise barren dull gray soil. Daisies grow best at 22.5°C but can tolerate temperatures between 5°C and 40°C. DaisyWorld has a neighboring planet, “BarrenWorld”, with no daisies or other life. As you’ll soon see, DaisyWorld and BarrenWorld surface temperatures respond very differently to changes in solar luminosity (which is a measure of the amount of solar radiation being emitted by the Sun).
Now try the Single Daisy Ecosystem challenge.
GRAB YOUR POINTS!
1. Log into eFolio. The link below will place your work into the eFolio and give you the Mini Survey.
GOING CRAZY
Let’s ramp up our investigation into DaisyWorld and consider a two daisy (black and white) environment, as originally designed by Lovelock. The version of the DaisyWorld model you should use for this challenge can be accessed here. This model will give you output data that you can use for graphing purposes. Play with the model a bit to see how it works.
Now, see what you can do with this Two Daisy Ecosystem modeling problem.
So where does the Gaia Hypothesis stand today? Well, there have been various interpretations of it, ranging from the idea that Earth’s biota has radically altered its environment to the belief that life on Earth is involved in a self-regulating system such that Earth’s environment is maintained in an steady state that is conducive to life to other, more far-flung views, that suggest intent (or even “consciousness”) on the part of Earth to create conditions suitable for its survival. The relatively new field of Earth Systems Science has incorporated some ideas from the Gaia Hypothesis and recognizes the need to study Earth as a whole system of interconnections and feedback mechanisms. This comes at a time, of course, when our need to accurately model Earth’s climate is pressing, and current climate models are often criticized for failure to include various climate-related processes, such as the effect of cloud cover. The study of extremely complex systems such as Earth is the subject of much exciting research today. 1, 2, 3, 4
GRAB YOUR POINTS!
1. Log into eFolio. The link below will place your work into the eFolio and give you the Mini Survey.
If You Need Help
If you have specific questions about this exploration, please contact your STEM Mentor. If you still have questions, please email Susan Hull Grasso, GCA Director of Curriculum Development; or "Skype" her.