a great part of our Earth. Hills and mountains are made of rock,
valleys and seas rest over rocks; rocks are the best chronicle of
Earth's past. By studying our native indian's stone utensils we
may determine facts about their culture. Even the traces of animals
that no longer exist, carved in rock in different places around
the world, help us reach conclusions about our Planet's prehistoric
era. Therefore, great part of what we know about our past has been
learned from rocks.
Eventhough some may state the contrary, it is mistaken to believe
that rocks never change. Day to day variations are imperceptible,
but the truth is they are constantly changing their shape and size.
These variations are generally very slow, but incessant. Cracks
are commonly visible on rocks, fragments often loosen around them,
causing the rock mass to diminish. Wind and water, little by little,
also wear them out. The day inevitably comes when after decades,
centuries, or milleniums only a few grains of sand or diminute particles
of mud remain in place of the rock. What was once stone, slowly
converted into soils and, some of these, dragged by rivers, filled
out interior valleys.
Other soils, sands, clays, or muds are dragged to the bottom of
the sea, where they settle and create layers. The weight of the
top layers cause the consolidation of particles of soil in the lower
layers to the point where, with time, they turn into rocks. In other
words, worn out rocks make up soils that evolve into rocks which,
in turn, are worn out and converted into soils that later consolidate
to make up rocks.
Many other changes occur at the Earth's surface. Powerful natural
forces cause layers of rock to rise and form mountain ranges. This
may happen as well on the bottom of the seas, causing volcanic cones
to emerge from their depths and form islands like Martinique and
Saba, on the Caribbean, and some islands on the Pacific. In other
places, segments of Earth's crust have sunken, and the surrounding
water has precipitated to the spaces left unoccupied, forming new
Many millions of years ago, turbulent seas covered what we know
today as the Antilles including Puerto Rico and parts of North America.
The incesant changes to which our Earth is subjected force rocks
to emerge over the ocean's surface in some cases, and in others,
to submerge under it. In some places these risings and sinkings
or submersions have appened many times, as they have in the little
piece of Earth we call Puerto Rico. This is why we need to be familiar
with a country's geology to be able to appreciate it more and know
Geology is the scientific study of what occurred and what is occurring
on the surface of the Earth; it studies the characteristics of the
terrestrial cortex , the variations occurring on it, and the natural
forces causing them. Some of the related subjects that geologists
tend to are the accumulation of minerals, the formation of rocks
and soils, the changes in elevation (sinkings and risings), earthquakes,
volcanic erruptions, and erosion.
Geologists have determined that rocks can be classified in three
groups according to their origin: igneous rocks, like granite and
andesite, of volcanic origin; sedimentary rocks, like limestone
and sandstone, formed by the action of wind and water; and metamorphic
rocks, like marble and serpentine, which were originally igneous
or sedimentary, but suffered changes over time mainly due to the
effects of heat and pressure.
In order to know Earth better, geologists make explorations, magnetic
studies and chemical analisis. In their studies, they make use of
X rays and Geiger counters, which are radioactivity detectors. During
the last ten years, the use of new scientific methods and technology
in geological investigations carried out in Puerto Rico has permitted
a better evaluation of the existence, extraction, and exploitation
of rocks and their minerals.One of geology's most important contributions
to human understanding is its concept of the long time elapsed since
the history of the Earth began.
Man's history makes up a very insignificant part of this extension.
A long, extremely long, time had to pass for the surface of the
Earth to reach its current state. A political history student speaks
of decades and centuries, a geology student refers to periods of
20 to 40 million years and to eras, which are even longer periods.
A long time has passed since valleys, mountains, rivers, beaches,
rocks and soils in Puerto Rico began to take shape.
Trough their studies of rock composition and structure, and of their
superposition anddisintegration, geologists have amplified our concept
of time. They have also studied fossils, which contain many rocks
and are evidence of life in the past.
With these studies they try to reach an understanding of how terrestrial
materials are formed and changed as a result of the action of natural
forces operating through time; and they try to reconstruct the geological
history of continents, countries and regions. Then, they investigate
how to apply the knowledge they have acquired by studying Earth's
Geologists search for scientific answers to the following questions:
What happened? How did it take place and how will what happened
affect us? What might happen in the future? In what way can
we use our knowledge to better our environment, our culture, and
our economy? Each of us may have also asked ourselves questions
like these many times in an effort to know more about our world
and our Island.
Rosa Navarro Haydon
by: Karen Mojica Franceschi