August 21 & 23rd, 2002

Env. Sci. 101 Lecture 2 & 3

The scientific method, systems, feedback and Daisyworld

 

Grant’s course, my syllabus on web, book in the library

 

SCIENCE

 

Not until the modern times, was science conducted in rational way. 

 

Francesco Redi (conducted ‘closed-off container study in late 17th century).  Later supported by Louis Pasteur (1865).

 

Copernicus realized that the Earth revolved around the sun.  Supported by Galileo, who was forced to recant his views.

 

What are important – basic – facts in the Earth Sciences?

 

 

Up until recently, best estimates were around 6,000 old (in Europe and U.S. based on the Biblical chronologies. 

Early time was not based on scientific fact.  It wasn’t until some 40 years ago that the age of the Earth was determined to be 4.65 billion years old.

 

If something can’t be tested, it isn’t science.  Note that anyone who had the knowledge in any society in the world would eventually determine that the Earth goes around  the moon.  In contrast, ‘facts’ based on religion are peculiar to a particular religion.  The age of the Earth is given as some 6,000 years in the Bible.  But Buddhist  ideas would be different.  The scientific-based ages will be the same everywhere.

 

 

Prior to 1795, most people believed change in the Earth was catastrophic.  None of the catastrophes could be explained by normal laws or processes, and so supernatural forces were required, which didn’t require explanation.  The great flood, etc. 

 

Using methods of observation, James Hutton realized that the slow processes that go on all around him could explain all of the things in the natural world.  Slow erosion could explain sedimentary rocks,  and there must be mountain building.  His idea was the Theory of Uniformitarianism, that things are mostly the same through time.  No catastrophes are needed.   “The present is the key to understanding the past”.  Now we use evidence in the past to say things about the present – we must understand past climate to know what will happen in the future.

 

Around 1980 an amazing discovery was made by Walter Alverez.  He recognized that the dinosaurs went extinct 65 million years ago as a result of a giant meteorite impact in the Yucatan Peninsula.  This was a return to the idea of catastrophism, but now it could be explained and tested.

 

Biology has its own impact.  It affects the planet greatly.  It has changed the atmosphere to one that contains oxygen.  Plants help hold down soil, and the acids that they give off can also erode rocks.  Temperatures of the planet are greatly affected by life on our planet.  After our billions of years of slow evolution (with occasional catastrophes), the Earth had reached a steady-state equilibrium.  Now in the last several millennia, we have changed all that.  We have caused a huge number of extinctions, modified climate, chemistry of our planet.  We are, in fact, a catastrophic (for better or worse) event in Earth history.  Change is difficult to adapt to, so in that sense, the changing we have made to our planet is bad.  But there can be no doubt that quality of life at the present time is at least as good as at any time in the past.

 

How old is the Earth.  Consider the following:

 

 

Time is what sets Earth Science apart from other

sciences.  The unidirectional nature of time.

 

 

 

 

 

 

 

 

 

 

 

The scientific method

 

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Science is a method of learning and understanding.  It advances by application of the scientific method, that is, the use of evidence that can be seen and tested by anyone with resources who cares to do so.

 


1) Observation

2) Hypothesis

3) Testing of hypothesis

4) Modify or rejecting

5) Accepting

6)   Eventually, becomes law  (example: heat flows from hot to cold).

7)      Some ‘laws’ have not been proven.  Gravity is the best example.  We don’t know how it works.

 

If it can’t be tested – if attempts cannot be made to disprove it -- then it’s generally not a good hypothesis.  Einstein’s theory of relativity couldn’t be tested for some time.  But finally a test came along, and the theory was and found to hold on the basis of the apparent shifting of stars, due to the suns gravitational field.

 

Example of a scientific study.  What is the optimal temperature for plants to survive?

 

Observations are first made.  The plant isn’t found to live in cold climates, nor in the deserts.  So it doesn’t like too hot or too cold.  But there’s less rain in the desert.  How do we know that it isn’t a function of water.  We must remove the ‘dependent’ variables.  Make a laboratory experiment.  This further strengthens the argument that there is an optimal temperature range, but doesn’t address the needs of water, etc.  It was a ‘controlled’ experiment, where all variables were kept constant except temperature.

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Another example:  Do ants sleep at night?

 

How to Prove Something; Do cigarettes cause cancer?

            It is easy to determine certain things.  Jump out of an airplane without a parachute and it will be fatal.  How about cigarettes cause cancer?

·        Scientific test:  Give someone a cigarette and see if they get cancer.  Obviously that doesn’t work.

·        Give one person cigarettes, and the other none.  Wait 50 years.  Not feasible.

·        Look at who gets cancer.  But now you have to deal with possible ‘linked effects’.  More cigarette smokers are also coffee drinkers out of Styrofoam cups?

·        Lets turn to rats.  Give a rat a cigarette.  Nothing happens.  Give him 10,000 cigarettes.  Now he gets cancer. 

·        But maybe 10,000/day are bad, but 5/day are totally fine.  How to test this?  Get a million rats.  Tried, but not successful.

·        And, how do we know rats are the same as people?

 

The system concept: 

 

“The ability to divide a complex problem into smaller, more easily studied pieces”. 

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A system is any part of the Universe that can be isolated for the purposes of observing and measuring changes. 

 

Examples of the usefulness of systems is illustrated with the human body.  Extremely complex, but it can be divided up into systems.  The cardiovascular system, the digestive system, etc.  And these can be divided up into components.   For example, the digestive system is divided up into the components small intestine, large intestine, stomach, esophagus, etc.

 

The planet is  a system.  A lake is a system.  A beaker is a system. 

 

The planet is an obvious one, while a lake seems too ‘small’ to be a system.  But we can consider the habitat of a particular fish population in terms of the lake system.  There are various components, such as the input river, the output river, the bottom, the surface, the mass of water, etc.  Vary the features of these components (such as the rate of flow into the lake) and the population of fish are effected. 

            Even though the planet seems like an obvious and complete system, it too is part of a smaller system.  There’s our solar system, with meteorites bombarding the surface of our Earth, sunlight heating our planet, etc.

 

We can divide systems into one of three types.

 

FEEDBACK:

 

Feedback is a very important phenomenon in the geological sciences.  It is when the output enters the box again as an input.  It is a method of self regulation, either stabilizing or destabilizing.  WE WILL BE DISCUSSING FEEDBACK LOOPS EXTENSIVELY IN THIS COURSE.

 

Negative feedback: When the system response is the opposite direction from the output.  Stabilizing systems are negative feedback.

 

Examples of negative feedback:

 

Albedo: The reflectivity of a surface is called its albedo.  Dark surfaces absorb more than light ones.  The white line on the roadway is cooler than the black.  White roads in cities would save a great deal in summer cooling bills.  Snow doesn’t melt very fast because it is white and has a very high albedo

 

Type of Surface                        Albedo

sand                                         0.2-0.3

grass                                        0.2-0.25

forest                                        0.05-0.1

water (sun overhead)                0.03-0.05

fresh snow                                0.80-0.85

thick cloud                                0.7-0.8

 

Positive feedback is when the perturbation of a system causes a further perturbation.  This results in a runaway system.  

 

In general, negative feedback is good – it is stabilizing; positive feedback is unstable.

 

Gaia  James Lovelock had the idea that biology controls its environment.  Plankton control the greenhouse effect, forest fires regulate O2 concentrations.  He came up with the term Gaia after the Greek earth goddess. 

His simple example of plants controlling the Earth is given in the idea of Daisyworld.

 

Daisyworld. or “How life can control it’s environment – the living Earth”

 

The idea of temperature vs. Daisy coverage.

 

A manned mission takes place to a faraway planet in another galaxy.  The only life form on the planet is white daisies.  Otherwise the surface is covered with a dull gray soil.  The astronauts decide to call the planet marigold world (no just kidding, they call it DaisyWorld for reasons that escape me).  After some experiments, the astronaut-scientists discover that the temperature on the planet is just about perfect for the daisies.  If is a bit hotter, they start dying off, and a bit cooler, they die as well.  The scientists also notice that the luminosity of the sun in the galaxy is increasing rapidly.  On the basis of the increased light from the sun, they conclude that the daisies will all die off within 100 years.  But they are wrong.  Why?

 

 

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First of all, we consider albedo.   Daisies have a higher albedo than the gray soil of the planet.  So if we increase daisy coverage, albedo goes up and temperature goes down.  This is seen in the following diagram.

 

 


Now consider the unrelated effect of temperature on daisy coverage.  There is an optimal temperature for daisies to grow.  Too hot, and the abundance of daisies decreases.  Likewise, too cold and they decrease as well.  Like the above figure, this can be seen in the following figure.

 

 

 

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Now, we can combine the two curves, because they are both plotting daisy coverage against the average surface tempeature.  When we do, we have the following diagram.

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There are two points on the diagram which are stable.  These are where the two sets of curves cross.  Consider any other point, and you will see that the configuration is not stable.

 

Stability, metastability, and unstability.  A stable condition is where a small perturbation to the system results in it returning to its previous state.  A ball in a trough, or a ruler on its side are two stable configurations.  A metastable configuration is one that is stable, but with even a small perturbation, it will become unstable and go to a more stable state.  The ruler on end, or a ball balanced on the top of a hill are examples.  Finally, an unstable configuration is one that does not remain in that condition for any period of time.  An example is a ball on the side of the hill, or a ruler at an angle.

 

Back to our Daisyworld model.  Let us look at point P1.  This is the stable configuration.

If we pull up some daisies (i.e. change the abundance of daisies on the surface), we will quickly come back to the equilibrium position, as seen by the following figure.

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On the other hand, at P2, we are at an metastable 'equilibrium', where any perturbation will cause a change to either a catastrophic situation or position P1.

 

Back to the idea of the solar luminosity increasing enough to kill off the daisies.  If we increase the solar radiation, we will shift the position of curve 1, but not change 2.  If we increase the intensity of sunlight, then the temperature of the planet’s surface will increase for the same amount of daisies.  This is seen in the following figure.  But, the optimum temperature and temperature range of daisy growth will not change (unless there are some very rapid evolutionary changes that occur).

 

 

CONCLUSIONS:      

·        A planetary system is not passive in the face of internal or external influences.

·        The response of life to pertubations is 'intelligent'.  Self-regulation is a common property to many natural systems.

 

 

 

 

 

 

 

 

 

 

 

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