Which statement best describes how an existing theory is often affected by the development of new technology?

an existing theory is thrown out and replaced with a completely new theory based on the new observations.
an existing theory is modified so that it can explain both the old and new observations.
an existing theory remains the same because a theory is a proven fact that is always true.
an existing theory is kept unchanged while a new theory is developed to explain the new observations.

An existing theory is modified so that it can explain both the old and new observations.

A theory is a well-confirmed explanation of a phenomenon, most of the time associated with scientific studies. It requires the use of a consistent scientific method, which includes observation and experimentation. A theory should be written in a way that allows for it to be proven wrong. Theories are often challenged when new evidence comes to light, and this is the main way in which science progresses. When this happens, theories are usually modified in a way that explains both past and present phenomena.

the earth’s crust is broken into separate pieces called tectonic plates (fig. 7.14). recall that the crust is the solid, rocky, outer shell of the planet. it is composed of two distinctly different types of material: the less-dense continental crust and the more-dense oceanic crust. both types of crust rest atop solid, upper mantle material. the upper mantle, in turn, floats on a denser layer of lower mantle that is much like thick molten tar.

each tectonic plate is free-floating and can move independently. earthquakes and volcanoes are the direct result of the movement of tectonic plates at fault lines. the term fault is used to describe the boundary between tectonic plates. most of the earthquakes and volcanoes around the pacific ocean basin—a pattern known as the “ring of fire”—are due to the movement of tectonic plates in this region. other observable results of short-term plate movement include the gradual widening of the great rift lakes in eastern africa and the rising of the himalayan mountain range. the motion of plates can be described in four general patterns:

collision: when two continental plates are shoved together

subduction: when one plate plunges beneath another (fig. 7.15)

spreading: when two plates are pushed apart (fig. 7.15)

transform faulting: when two plates slide past each other (fig. 7.15)