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Scientific Method Help

By — McGraw-Hill Professional
Updated on Aug 31, 2011

Scientific Method

Just as Nicolaus Steno in the late 1700s began describing his three laws of relative dating based on his observations, so other scientists wanted to solve the Earth’s mysteries. They wanted to understand all the workings of the Earth and to do this, they used the scientific method .

The keys to the scientific method are curiosity and determination, observation and analysis, measurement and conclusion. As humans, we are curious by nature. Throughout this book, you will get to know the tools and techniques that earth scientists use to find out all they can about our big, blue planet.

First, they start with a hypothesis like “fire burns” or “the Earth is flat.” Then, they write down their observations about their hypothesis like “when fish is cooked too long over a fire, it turns to charcoal” or “on a calm day, the ocean is flat all the way to the horizon.” People might follow a hypothesis for hundreds of years believing it to be absolutely true and then one day notice a new observation that presents doubt or completely proves it wrong.

A hypothesis is a statement or idea that describes or attempts to explain observable information.

More and more information is gathered about the hypothesis like “all wood burns in a fire” or “fields of grain stretch for miles out upon the flat plain.” Scientists then and now check to see if their observations always fit in different locations. Are all fires hot? Are all deserts flat? How do the tallest mountains fit into the picture? What are volcanoes and why are they hot?

A theory comes about through careful testing and confirmation of a hypothesis over time.

Following years of testing by many scientists, experimental data is gathered that either supports a theory or blows it apart. (Always awkward when some segment of the scientific community wants to defend a favorite theory to the end.)

A theory predicts the outcome of new testing based on past experimental results. When a theory is found to be untrue, like when someone notices that the Earth’s shadow on the Moon during eclipse is curved, not straight as a flat-edged ruler, then more observations and testing must be done to see if a new theory is needed.

The Four Theories

To explain the differences in the size, shape, moisture, and composition of the landforms around the world, scientists presented the following theories:

  1. Contraction theory,
  2. Expansion theory,
  3. Convection theory, and
  4. Combination theory.

The contraction theory is the simplest theory stating that when the Earth originally cooled from the molten state, it became wrinkled and cooled unequally. The areas of hot and cool rock caused stresses that pulled, pushed, and compressed the land into different forms.

The expansion theory is roughly the reverse of the contraction theory. This theory suggests that the Earth was originally one-half of its present diameter of 12,756 km. It states that when the Earth cooled unequally at the beginning, there was an expansion of the faults and that gigantic blocks in the crust (about the size of Texas) were shoved up and out from the molten core. This led to increased volcanic eruptions and growing expansion of land from the seas.

In the convection theory , the upswelling of the land materials is thought to have happened through the circulation of magma or melted rock. As it expanded and pushed upward, it lost heat. The nearer the surface it got, the more it cooled and the denser it became. It turned into hard rock. When this happened, the hardened magma began to sink back down where it was heated, melted, and eventually started rising again. Scientists felt this theory explained the constant heat from the mantle and the increasing pressures.

The combination theory takes a bit from all the other theories and puts it together. In combination theory, the source of the energy that drives all this movement is thought to be the decay of naturally occurring radioactive elements supplying constant energy for the steady heating of the magma. In the combination theory, the crust is described as expanding along fracture lines, shoving broken blocks of crust apart, and making the pressure increase. Mountains are thought to be formed from a combination of melted rock and the folding and grinding of the landmasses sliding along on the “flexible” mantle.

In addition to the movement of the landmasses, scientists found another clue to support their theories. The composition of land rock and ocean rock was different. It was discovered that much of the landmass was made up of granite, while oceans contained mostly basalt.  Figure 3-6 shows the densities of granite and basalt. The movement of landforms is smooth when there is a lot of space. It can shift abruptly from pressure buildup after more land is packed into a tighter space. If you put a few grocery items on top of a carton of eggs in a paper bag, the eggs will be fine in their box. However, if more and more heavy items are piled into the bag, the pressure on the top of the egg carton increases and the eggs will break.

On the Inside

Fig. 3-6. Granite and basalt have different densities.

A law is a hypothesis or theory that is tested time after time with the same resulting data and thought to be without exception.

When the same results are obtained over and over by a variety of experimenters, like “fire is always hot and burns in camp sites, farms, villages, cities, laboratories, and everywhere,” then a theory is proven as a law . Over many years and repeated testing, laws are thought to be set in stone. If a new theory is developed, information is added to or takes the place of old ideas, and the cycle begins again. It takes a lot of testing and discussion for it to become a law.

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