THE PHYSICAL ENVIRONMENT
THE EARTH'S MATERIALS AND INTERNAL PROCESSES
How thick is the Earth's crust?
The thickness of the Earth's crust varies at different points around the planet. Under continents, the crust is approximately 15 miles (24 kilometers) thick, but under the oceans it is a mere five miles (8 kilometers) thick.
What is continental drift?
The Earth is divided into massive pieces of crust that are called tectonic plates. These plates lie wedged together like a puzzle. The plates slowly move, crashing into each other to form mountain ranges, volcanoes, and earthquakes. The plates are like rafts floating on water; this is called continental drift.
How many tectonic plates are there?
There are a dozen significant plates on the planet. Some of the largest include the Eurasian Plate, North American Plate, South American Plate, African Plate, Indo-Australian Plate, Pacific Plate, and Antarctic Plate. Some smaller plates are located between the major plates. The smaller plates include the Arabian Plate (containing the Arabian Peninsula), the Nazca Plate (located to the west of South America), the Philippine Plate (located southeast of Japan, containing the northern Philippine islands), the Cocos Plate (located southwest of Central America), and the Juan de Fuca Plate (just off the coast of Oregon, Washington, and Northern California).
Earth's tectonic plates are in constant motion, causing geologic fault lines like this one, formed in a strata of volcanic ash that was cut open during road construction.
What was Pangea?
Pangea, which existed about 250 million years ago, was one huge continent, including the land of all seven continents. It was located near present-day Antarctica and has slowly drifted and split to form the continents as we know them today. The continents and their tectonic plates continue to move and will one day be in a much different arrangement than they are today.
How are mountains formed?
The process of progeny, or mountain building, is related to continental drift. When two tectonic plates collide, they often form mountains. The Himalayas are the result of the Indo-Australian plate colliding with the Eurasian plate. At these collision zones, volcanoes and earthquakes are common.
How did the Himalayas form?
About 30 to 50 million years ago, the landmass of India pressed into the landmass of Asia, pushing up land at the place of impact and creating the Himalayas. Even today, as the Indian subcontinent presses against Asia, the Himalayas continue to grow and change.
What type of rocks are formed by lava?
Igneous rocks are formed when liquid magma under the surface of the Earth, or lava on the surface of the Earth, cools and hardens into rock.
What type of rocks are formed from particles?
Sedimentary rocks are formed by the accumulation and squeezing together of layers of sediment (particles of rock or remains of plant and animal life) at the bottom of rivers, lakes, and oceans or even on land. The continual accumulation of more and more layers of sediment places a great amount of pressure on the lowest layers of sediment and, over time, compresses them into rock.
What are recycled rocks?
Metamorphic rocks are recycled rocks. Metamorphic rocks are rocks that had a prior existence as sedimentary, igneous, or even another metamorphic rock. Underground heat and pressure metamorphose one type of rock into another, creating a metamorphic, or recycled rock.
What type of sand do we often see on beaches near volcanoes?
Because of the content of the sediment near volcanoes comprised of dark black igneous rock, the resulting beach sand in such places as Hawaii and Indonesia is actually a dark brown, even black in color.
Which is larger, clay or sand?
A single grain of sand is 1500 times larger than a grain of clay. What is a dike?
A dike is magma that has risen up through a crack between layers of rock. When this magma solidifies, it becomes very solid rock. If the rock around it is eroded, a dike can form great rock monoliths above the ground.
What are hot springs?
Hot springs are created by underground water that is heated and percolates to the Earth's surface. Aside from being natural baths, the steam from hot springs can be used to drive turbines, which create electricity. This type of energy production is called geothermal energy.
Where are hot springs used by people around the world?
Hot spring baths have been used in cultures throughout the world since ancient times. They are found in such places as Japan, Taiwan, Australia, the United States, Iceland, and Sicily.
Why does the ground sink?
In many places over the world, seemingly solid land lies over vast oil deposits or water aquifers. Without the liquid supporting it, the ground sinks into the space left behind. In some parts of California's Imperial Valley, the land has dropped more than 25 feet (7.6 meters) due to underground water being removed from the area. Unless the pumping of underground water and oil is stopped, the land will continue to sink.
Why do houses fall into sinkholes?
Houses that sit upon limestone rock have the proclivity to fall into sinkholes. As underground water wears away the limestone rock, it creates underground caverns. If the water wears away too much limestone, the cavern may collapse, taking anything on the surface with it. A sinkhole is just one of the many reasons to have your home inspected by a geologist.