The earth is more than 4.5 billion years old! During this unimaginable expanse of time, our planet has undergone drastic changes. For the earliest part of earth’s history, the planet was a molten inferno. As the planet slowly cooled, rocks and minerals began to form, and continents and ocean basins took shape. Earth’s continents today look nothing like they did hundreds of millions of years ago. In fact, the continents move around through a process called plate tectonics. The Theory of Plat Tectonics is relatively modern and is very different from historic thought, which included ideas ranging from shrinking earth to continents moving across the ocean floor. Fossil evidence paired with lithographic correlation helped solidify the concept of plate tectonics to the theory we know today.

1. The Earth Dynamics
The earth is more than 4.5 billion years old! During this unimaginable expanse of time, our
planet has undergone drastic changes. For the earliest part of earth’s history, the planet was a
molten inferno. As the planet slowly cooled, rocks and minerals began to form, and continents
and ocean basins took shape. Earth’s continents today look nothing like they did hundreds of
millions of years ago. In fact, the continents move around through a process called plate
tectonics.
The Theory of Plat Tectonics is relatively modern and is very different from historic thought,
which included ideas ranging from shrinking earth to continents moving across the ocean floor.
Fossil evidence paired with lithographic correlation helped solidify the concept of plate tectonics
to the theory we know today.
Continental crust (the thin outer skin of our planet) sits on top of hot rock material, called the
mantle, which behaves like cold syrup. The earth consists of dozens of major and minor plates
that move under, over and alongside each other at areas known as plate boundaries. There are
three different types of plate boundaries:
1. Divergent, where new crust is generated, and the plates move apart.
2. Convergent, where old crust is recycled, and plates move toward each other; and
3. Transform, where crust is neither created or destroyed and the plates slide alongside
each other.
At these plate boundaries, plates react with one another differently based on their composition.
The denser oceanic plates tend to sink, while the less dense continental plates do not.
As the plates shift, they can collide, causing mountain ranges and deep ocean trenches, and
they can slide past one another along long faults, like the San Andreas fault, and they can
spread apart as seen along mid-ocean ridges. Plate tectonics describes the processes involved
in plate motions and allows geologists to understand how earth’s plates, of which Florida is a
part, came to be. Modern research has taught us that earth is a truly dynamic planet.

2. Any discussion of the role of plate tectonics in Earth dynamics and history has to start with a
definition of plate tectonics itself and go on to establish how it might be recognized in the rock
record. Speakers at the meeting gave a variety of definitions that included four elements: strong
rigid lithosphere plates; weak persistent plate margins; horizontal movement relative to other
plates; and circulation between the surface and deep Earth. All agreed that the term “plate
tectonics” refers to the global system of coupled ridges, trenches and transform faults that
defines the surface of the Earth today. One element of the system is not enough to deduce that
the planet-wide cycles are operating.
• Strong lithosphere. Development of strong rigid lithosphere matters for plate tectonics
because Earth today has plates thousands of kilometers wide, able to transmit stress
from one side to the other. The cold ocean lithosphere is ∼1% denser than the mantle
immediately beneath; this gravitational instability means that subduction continues once
a plate slides into the mantle below at a plate margin.
• Plate boundaries. While today's plates are strong, the margins where the relative
movement takes place are weak. Oceanic plate boundaries are up to thousands of
kilometers long but only tens of kilometers wide, defined by the earthquakes that indicate
fault motion in the upper parts of the plates. Continental plate boundaries are wider but
are also defined by fault zones. The problem for the inception of plate tectonics is how to
develop such long-lived linear weak zones.
• Relative movement. The horizontal motion of the plates, at speeds around a few
centimeters per year, is another characteristic of plate tectonics. But the driving
mechanism remains unclear; there is no simple link with mantle convection. The ability
of the lithosphere to transmit stress plays a part in plate movements. At subduction
zones, the descending cold slab exerts a downward force – slab pull – on the rest of the
plate. The effects of lithosphere cooling, solidification and thickening at the mid-ocean

3. ridge also act to move the young plate away from the ridge. These forces in combination
may be enough to sustain subduction once it has started.
• Chemical cycles. The subduction of the lithosphere in plate tectonics plays an
important role in cycles that move elements important for life between the deep Earth,
surface, oceans, and atmosphere. Weathering of silicate rocks by rainwater acidified in
the atmosphere brings carbon and oxygen into the oceans and ocean sediments;
subduction takes those volatile components into the mantle, where some of them are
returned to the atmosphere in volcanic eruptions. This cycle acts as negative feedback
on global temperature change, acting faster when the temperature is higher, for
example.
Similar cycles between the atmosphere and deep Earth operate for other volatile elements and
may be important in maintaining nutrients for life through geological time.