John Jacobs, age 10, of Portland, Ore., for his question:
WHAT IS GEOLOGY?
Geology is the study of the earth. Scientists called geologists study mountains, rocks, oceans, caves, rivers, soils and other parts of the earth and then they try to tell us how the earth was formed and how it changes.
There are two main fields of geology: physical geology and historical geology. Physical geology is the study of the materials that make up the earth and the forces that shape the earth. Historical geology deals with the history of the earth.
The word geology comes from the Greek words ge, which means earth, and lagos, which means study.
The first people to study and write about the earth were the ancient Greeks. Many of their writings were a mixture of facts, superstitions, legends, guesses and the beliefs of the time.
A bit later, the ancient Romans contributed writings in geology that were more realistic than those of the Greeks. Then from about A.D. 400, little scientific advancement took place for about 600 years. In the early 1020s, a Persian physician named Avicenna wrote an important book on the origin of rocks, meteorites and mountains.
The Renaissance was a period of renewed interest in many fields of learning including the study of the earth. A Polish born astronomer named Nicolaus Copernicus came up with suggestions that the earth rotated on its axis every 24 hours and around the sun once a year. He also said that the planets circled the sun and that the moon revolved around the earth.
A Danish physician named Nicolaus Steno made a great geological discovery in 1669. He demonstrated that the strata or layers of rock are always deposited with the oldest layers on the bottom and the youngest layers on top. This helped geologists determine the order in which geological events took place.
Geology tells us that the earth probably was formed more than 4.5 billion years ago. It has certainly changed in many ways since then. Many of these changes take place slowly and will continue as long as the earth lasts.
Earthquakes lift large pieces of land and move them to create mountains and other general changes on the surface of the earth. Hot molten rock called lava flows from volcanoes and then cools, forming hard rock.
Great rivers of ice called glaciers creep down from mountains carrying rocks and soil with them. When the glaciers melt, they leave the rocks and Boils behind them on the lowlands or in the ocean.
Some of the branches of physical geology include meteoreology, which is the study of the atmosphere and weather, petrology, which is the study of rocks, and minerology, which is the study of minerals.
Other important branches include oceanography, which is the study of oceans and life in the ocean, and structural geology, which is the study of the position and shapes or rocks deep within the earth and the causes of changes in these rocks.