FACTORES HISTÓRICOS

La tierra un planeta dinámico

According to the

continental drift

theory, the

supercontinent

Pangaea began to

break up about 225-

200 million years

ago, eventually

fragmenting into

the continents as we

know them today.

The layer of the Earth we live on is broken into a dozen or so rigid slabs (called

tectonic plates by geologists) that are moving relative to one another.

As noted by Snider-Pellegrini and Wegener, the locations of certain fossil plants and

animals on present-day, widely separated continents would form definite patterns

(shown by the bands of colors), if the continents are rejoined.

These four diagrams illustrate the shrinking of the formerly very large Farallon Plate, as it was progressively

consumed beneath the North American and Caribbean Plates, leaving only the present-day Juan de Fuca,

Rivera, and Cocos Plates as small remnants. Large solid arrows show the present-day sense of relative

movement between the Pacific and North American Plates.

Alfred Lothar

Wegener (1880-

1930), the

originator of the

theory of continental

drift. (Photograph

courtesy of the

Alfred Wegener

Institute for Polar

and Marine

Research,

Bremerhaven,

Germany.)

DESARROLLO DE LA TEORIA

The mid-ocean ridge (shown in red) winds its way between the continents much like

the seam on a baseball.

Computer-generated detailed topographic map of a segment of the Mid-Oceanic Ridge.

"Warm" colors (yellow to red) indicate the ridge rising above the seafloor, and the

"cool" colors (green to blue) represent lower elevations. This image (at latitude 9°

north) is of a small part of the East Pacific Rise.

A theoretical model of the formation of magnetic striping. New oceanic crust forming

continuously at the crest of the mid-ocean ridge cools and becomes increasingly older

as it moves away from the ridge crest with seafloor spreading (see text): a. the

spreading ridge about 5 million years ago; b. about 2 to 3 million years ago; and c.

present-day.

The center part of the

figure -- representing the

deep ocean floor with

the sea magically

removed -- shows the

magnetic striping

mapped by

oceanographic surveys

offshore of the Pacific

Northwest. Thin black

lines show transform

faults that offset the

striping

Crecimiento del fondo marino y

reciclamiento de la corteza oceánica.

View of the first high-temperature vent (380 °C) ever seen by scientists during a dive of

the deep-sea submersible Alvin on the East Pacific Rise (latitude 21° north) in 1979.

Such geothermal vents--called smokers because they resemble chimneys--spew dark,

mineral-rich, fluids heated by contact with the newly formed, still-hot oceanic crust.

This photograph shows a black smoker, but smokers can also be white, grey, or clear

depending on the material being ejected.

The deep-sea hot-spring environment supports abundant and bizarre sea

life, including tube worms, crabs, giant clams. This hot-spring

"neighborhood" is at 13° N along the East Pacific Rise.

The manipulator arm of the research submersible Alvin

collecting a giant clam from the deep ocean floor. (Photograph

by John M. Edmond, Massachusetts Institute of Technology.)

The size of deep-sea giant clams is evident from the hands of a

scientist holding them. (Photograph by William R. Normark, USGS.)

A colony of tube worms, some as long as 1.5 m, clustered around

an ocean floor hot spring.

Close-up of spider crab that was observed to be eating tube worms.

The JOIDES Resolution is the deep-sea drilling ship of the 1990s

(JOIDES= Joint Oceanographic Institutions for Deep Earth

Sampling). This ship, which carries more than 9,000 m of drill pipe,

is capable of more precise positioning and deeper drilling than the

Glomar Challenger.

Concertación de sismos

As early as the 1920s, scientists noted that earthquakes are concentrated in very specific

narrow zones. In 1954, French seismologist J.P. Rothé published this map showing the

concentration of earthquakes along the zones indicated by dots and cross-hatched areas.