Plate Tectonics is a theory.
All theories (evolution, quantum mechanics, special/general relativity, big bang, etc.) sit on a sliding scale of “trustability” or truth.  Think of one end of the scale as well substantiated (lots of evidence/corroboration) and the other end as ideas or hypotheses that are less well constrained.

Sliding Scale of THEORIES
<<=====  Poorly Substantiated  xxxxxxx <=====> xxxxxxx   Well Substantiated =====>>

Plate tectonics (and really, every one of the others mentioned above) is way off on the right side of this scale!  A well substantiated theory that has enormous amounts of supporting and corroborating evidence.

Of course there are some geologic features and processes that plate tectonics doesn’t explain, but this doesn’t make it a bad theory, instead it just means that it can’t explain everything!.
In general plate tectonics is a highly substantiated (i.e. documented and trustworthy) theory that drives much of how we understand geology and the world around us!

Introduction

When it burst onto the scene in the 1960’s and 1970’s, largely because of developments in our understanding of the ocean floor (topography and magnetics– as we’ll see later in this chapter) plate tectonics became a kind of key that effectively unlocked the door to a host of prior geological puzzles.

Before plate tectonics, geologists really couldn’t provide good answers to questions like:

1. Do continents really move around on the face of the globe?  How do they do so?
2. Why are fossils and rock types often very similar on continents separated by 1000’s of miles of ocean
3. Have oceans basins actually changed over time?  Growing and shrinking?  How does this happen?
4. Why is the oceanic crust vastly younger than the oldest continental crust?
   Average age of ocean crust is only 100my or so, whereas continents can be in excess of 4000my.
5. Why are earthquakes and volcanos localized in bands and regions? (Like the “Ring of Fire” surrounding the Pacific Ocean, and including places like Japan and California.)
6. Do mountains come and go with time?  Of course they erode away, but what makes them form?  And why are some mountain ranges (e.g. Himalayas) vastly higher than others?
7. Why in the world (so to speak!) are the deepest parts of the ocean (oceanic trenches, upwards of 30,000 feet deep) often near the edges of ocean basins, near to continents?  Why would the deepest parts not be in the center of these ocean basins?

Plate tectonic theory actually provides answers to all of the above (and many other) questions.

What is Plate Tectonics?— it’s just the idea that the outer portion of the earth (the lithosphere) is mobile, and it leads to moving continents and changing shape of ocean basins.

Learning Outcomes

• Describe Continental Drift including supporting evidence.
• Critique and interpret major types of evidence supporting the Theory of Plate Tectonics.
• Describe different geological processes in relation to plate tectonics.