Earth Surface and Interior
The Earth’s surface and its interior are fundamental components of the Earth system influence and react to the dynamics of our oceans and atmosphere. Therefore, an understanding the dynamics of the solid Earth is essential to developing an interconnected view of Earth science and its applications that ranges from natural hazards and climate change to fundamental physics.
Earth, the largest and densest rocky planet, was formed about 4.5 billion years ago. The Earth’s interior is divided into four layers which is typical of rocky planets. Each layer has different characteristics and is made of different elements and minerals. There is a gradient in temperature between the cool surface and the hot interior with the center, or core,as hot as 9000 degrees F. The crust is broken into many large plates that move slowly relative to each other.
Mountain ranges form when two plates collide and their edges are forced up. In addition, many other surface features are the result of the moving plates. The plates move about one inch per year, so millions of years ago the continents and the oceans were in different positions. About 250 million years ago, most of the land was connected together, and over time has separated into seven continents.
Surface and Interior of Earth
Earth, the largest and densest rocky planet, was formed about 4.5 billion years ago. The Earth’s interior is divided into four layers, which is typical of rocky planets. Each layer has different characteristics and is made of different elements and minerals.
There are many different types of features on Earth’s surface due to the complexity of our planet. The surface is unique from the other planets because it is the only one which has liquid water in such large quantities. Water forms some features of Earth’s surface such as rivers, oceans, beaches and lakes. Other surface features, such as mountains, earthquakes and volcanoes, are formed when large pieces of the Earth’s outer layer move slowly by plate tectonics.
Surface and Earth
The Earth’s surface is home to spectacular and frightening sights and experiences that hint at what is happening deep within the planet. Volcanoes and earthquakes are powerful evidence of the tectonic plates that grind against one another and the magma that rises through an inner layer known as the mantle.
Plate tectonics, a theory central to modern geology, explains so much of what we see happening around us. Through this theory, we now understand how mountains form, why there are different types of volcano, and how the land surface is constantly renewed.
Surface of the Earth
Bound by cliffs and cut by erosion, canyons are deep, narrow valleys in the Earth’s crust that evoke superlatives and a sense of wonder. Layers of rock outline stories of regional geology like the table of contents to a scientific text.
The landforms commonly break parched terrain where rivers are the major force to sculpt the land. They are also found on ocean floors where the torrents of currents dig underwater graves.
Other canyons start where a spring sprouts from the base of a cliff as if out of nowhere. Such cliffs are composed of permeable, or porous, rock. Instead of flowing off the cliff, water seeps down into the rock until it hits an impermeable layer beneath and is forced to leak sideways. Where the water emerges, the cliff wall is weakened and eventually collapses. A box canyon forms as sections of wall collapse further and further back into the land. The heads of these canyons are marked by cliffs on at least three sides.
Slot canyons are narrow corridors sliced into eroding plateaus by periodic bursts of rushing water. Some measure less than a few feet across but drop several hundred feet to the floor.
Submarine canyons are similar to those on land in shape and form, but are cut by currents on the ocean floor. Many are the mere extension of a river canyon as it dumps into the ocean and flows across the continental shelf. Others are gouged from turbid currents that occasionally plunge to the ocean floor.
The deep waters of these oceans hide from view rugged mountains, vast plateaus, active volcanoes, and seemingly bottomless trenches. These underwater landscapes are in an endless cycle of construction and destruction as new crust is born along mid – ocean ridges, pushing old crust into the depths of the fiery mantle.
The highest and biggest plateau on Earth, the Tibetan Plateau in East Asia, resulted from a collision between two tectonic plates about 55 million years ago. The land buckled up along the seam of the collision and formed the Himalaya mountain range. Farther away, the crust uplifted but didn’t crumple and wrinkle, creating instead a raised, flat, and wide open expanse known as the “roof of the world.”
Many plateaus form as magma deep inside the Earth pushes toward the surface but fails to break through the crust. Instead, the magma lifts up the large, flat, impenetrable rock above it. Geologists believe a cushion of magma may have given the Colorado Plateau its final lift beginning about ten million years ago.
Because the crust is accessible to us, its geology has been extensively studied, and therefore much more information is known about its structure and composition than about the structure and composition of the mantle and core. Within the crust, intricate patterns are created when rocks are redistributed and deposited in layers through the geologic processes of eruption and intrusion of lava, erosion, and consolidation of rock particles, and solidification and recrystallization of porous rock.
By the large – scale process of plate tectonics, about twelve plates, which contain combinations of continents and ocean basins, have moved around on the Earth’s surface through much of geologic time. The edges of the plates are marked by concentrations of earthquakes and volcanoes. Collisions of plates can produce mountains like the Himalayas, the tallest range in the world.
The Earth’s Interior
Just as a child may shake an unopened present in an attempt to discover the contents of a gift, so man must listen to the ring and vibration of our Earth in an attempt to discover its content. This is accomplished through seismology, which has become the principle method used in studying Earth’s interior.
Seismos is a Greek word meaning shock; akin to earthquake, shake, or violently moved. Seismology on Earth deals with the study of vibrations that are produced by earthquakes, the impact of meteorites, or artificial means such as an explosion. On these occasions, a seismograph is used to measure and record the actual movements and vibrations within the Earth and of the ground.
Inside of the Earth
Minerals and Gems
More than 4,000 naturally occurring minerals — inorganic solids that have a characteristic chemical composition and specific crystal structure — have been found on Earth. They are formed of simple molecules or individual elements arranged in repeating chains, sheets, or three – dimensional arrays.
Minerals are typically formed when molten rock, or magma, cools, or by separating out of mineral – rich water, such as that in underground caverns. In general, mineral particles are small, having formed within confined areas such as lava flows or between grains of sediments. Large crystals found in geodes and other rocks are relatively rare.
Rocks themselves are made of clusters or mixtures of minerals, and minerals and rocks affect landform development and form natural resources such as gold, tin, iron, marble, and granite.
Extremely common in the Earth’s crust, igneous rocks are volcanic and form from molten material. They include not only lava spewed from volcanoes, but also rocks like granite, which are formed by magma that solidifies far underground.
Typically, granite makes up large parts of all the continents. The seafloor is formed of a dark lava called basalt, the most common volcanic rock. Basalt is also found in volcanic lava flows, such as those in Hawaii, Iceland, and large parts of the U.S. Northwest.
Granite rocks can be very old. Some granite, in Australia, is believed to be more than four billion years old, although when rocks get that old, they have been altered enough by geological forces that it’s hard to classify them.
The Structure of the Moon
The Moon, our fellow – traveler in space, has a diameter half that of the Earth’s core, and it revolves around the Earth, as all the planets revolve around the Sun, under the force of gravity. Moonquakes of very low energy are caused by land tides produced by the pull of Earth’s gravity, and, from analysis of moon quake data, scientists believe the Moon has two layers.
Crust – From the surface to 65 kilometers depth,
Inner – More dense mantle from the crust to the center at 3,700 kilometers.
The crust is presumed to be com – posed primarily of rocks containing feldspar, calcium aluminum silicate, and lesser pyrox – ene, iron and magnesium silicate; the crust also contains basalt in the mares, which con – tains less iron and more titanium than earth basalt. The mantle is thought to be made up of calcic peridotite, containing both pyroxene and feldspar.
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