Rocks in the oceanic crust contain more iron, and are therefore denser, than continental rocks. Because continental crust is thicker but less dense than oceanic crust, the continents ride higher by floating like buoyant rafts on the denser mantle, much as icebergs float on the ocean.
Rock can be solid and strong over the short term (seconds to years), but weak over the long term (thousands to millions of years). The mantle below 100km has little strength, and over very long periods, it flows as it adjusts to support the weight of continents and mountains.
The inner core is a solid metallic sphere suspended within the liquid outer core — a “planet within a planet.” The radius of the inner core is 1220km, about two-thirds the size of the Moon.
Geologists were puzzled by the existence of this “frozen” inner core. The knew that temperatures inside Earth should increase with depth. If the inner core is hotter, how could it be solid while the outer core is molten? The “freezing” was due to higher pressures, rather than lower temperatures, at Earth’s center.
Earth is a restless planet, continually changing through geologic activity such as earth quakes, vocalness, and glaciation. This activity is powered by 2 heat engines: one internal, the other external.
Earth’s internal heat engine is powered by the heat energy trapped in its deep interior during its violent origin and released inside the planet by radioactivity. This internal heat drives movement in the mantle and core, supplying the energy that melts rock, move continents, and lifts up mountains.
Earth’s external heat engine is driven by solar energy. Heat from the Sun energizes the atmosphere and oceans and is responsible for Earth’s climate and weather. Rain, wind, and ice erode mountains and shape the landscape, and the shape of the landscape, in turn, influence the climate.
In some ways, the outer part of the solid Earth behaves like a ball of hot wax. Cooling of the surface forms a strong outer shell, or lithosphere (from the Greek lithos, meaning “stone”), which encases a hot, weak asthenosphere. The lithosphere includes the crust and the top part of the mantle down to an average depth of about 100km. The asthenosphere is the portion of the mantle, perhaps 300km thick, immediately below the lithosphere. When subjected to force, the lithosphere tends to behave like a nearly rigid and brittle shell, whereas the underlaying asthenosphere flows like a moldable, or ductile, solid.
Rocks are naturally occurring aggregates of minerals.
Igneous rocks: Melting of rock in hot, deep crust and upper mantle. Forming process: crystallization (solidification of magma or lava).
Sedimentary rocks: Weathering and erosion of rocks exposed at surface. Forming process: disposition, burial, and lithification.
Metamorphic rocks: Rocks under high temperatures and pressures in deep crust and upper mantle. Forming process: recrystallization of new minerals in solid state.
In terms of surface area, most rocks found at Earth’s surface are sedimentary, but these rocks weather easily, so their volume is small compared with that of the igneous and metamorphic rocks that make up the main volume of the crust.
Finding a promising deposit is only the 1st step toward extracting useful materials, however. The shape of the deposit, and the distribution and concentration of the ore, must be estimated before mining begins. This is done by drilling closely spaced holes and obtaining continuous cores through the ore deposits and the surrounding rock. Information from the cores is used to create a 3D model of the ore deposit. That model is then used to evaluate whether or not not the deposit is large enough and has a high enough concentration of minerals to justify opening a mine.
A rock’s melting point depends on its chemical and mineral composition and on conditions of temperature and pressure.
Rock does not melt completely at a given temperature. Instead, rocks undergo partial melting because the minerals tha compose them melt at different temperatures.
Oceans may be thought of as huge chemical mixing vats.
Each of the many dissolved components of seawater participates in some chemical or biological reaction that eventually precipitates it out of the water and onto the seafloor. AS a result, the ocean’s salinity — the total amount of dissolved material in a given volume of water — remains constant.
Temperature increase with depth in Earth’s crust at an average rate of 30 degrees celsius for each kilometer of depth. Thus, at a depth of 4km, buried sediments may reach 120 degrees or more, the temperature at which certain types of organic matter may be converted to oil and natural gas. Pressure also increases with depth. This increased pressure is responsible for the compaction of buried sediments.
Pebbles and cobbles are abraded and rounded during transportation. Angular grains imply short transport distances; rounded ones indicate long journeys down a large river system.
Oil and natural gas come from organic matter that was buried in sedimentary rock formations at some time in the geologic past. The relative ages of these “petroleum source rocks” provide important clues about where to look for new oil and gas resources. Very little petroleum has come from Precambrian rocks, which makes sense, because the primitive organisms that existed before the Cambrian period generated little organic matter.
It is often said that you are what you eat, and that statement is true not only for humans, but for all organisms. Our foods are made up of more or less the same materials: molecules composed of carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur. So it doesn’t matter whether the organism is an autotroph or a heterotroph, it still utilizes the same 6 elements as food. What differs is the form (that is, the molecular structure) their food comes in.
Extremophiles:
- Halophile: high salinity.
- Acidophile: high acidity.
- Thermophile: high temperature.
- Anaerobe: no oxygen.
Greenhouse gases such as carbon dioxide and methane also play an important role in determining the habitable zone. Once the greenhouse gases were lost, Mars was transformed into the icy desert it is today.
Continental glaciers cover about 10% of the land surface, storing about 75% of the world’s fresh water.
Essentially all the energy driving the climate system ultimately comes from the Sun.
Greenhouse gases, such as water vapor, carbon dioxide, methane, and ozone, absorb energy and reradiate it as infrared energy in all directions, including downward to the surface. In this way, they act like the glass in a greenhouse, allowing light energy to pass through, but trapping heat in the atmosphere. This trapping of heat, which increases the temperature at the surface relative to the temperature higher in the atmosphere, is known as the greenhouse effect.
Salt water: 96%
Fresh water: 4%
- Glaciers and polar ice: 2.97%
- Underground waters: 1.05%
- Atmosphere: 0.001%
- Lakes and rivers: 0.009%
- Biosphere: 0.0001%
Per capita domestic water use in the US is 2-4 times greater than in western Europe, where consumers pay as much as 350% more for their water.
US water use by category:
- Thermoelectric power: 41.5%
- Irrigation: 37%
- Domestic use: 8.5%
- Public supply: 5.4%
- Industry: 5%
- Aquaculture: 2.6%
At the equator, hot air, which is less dense than cold air, rises and flows toward the poles, gradually sinking as it cools. The sinking air reaches ground level in the subtropic, then flows back along Earth’s surface toward the equator to form the trade winds. These air movements set up a global pattern of air circulation between the North and South poles.
This simple circulatory pattern of air flow is complicated by Earth’s rotation.
Although film and television portrayals might lead one to think that deserts are mostly sand, only one-fifth of the world’s desert area is actually covered by sand. The other four-fifths are rocky or covered with desert pavement. Sand covers only one-tenth of the Sahara, and sand dunes are even less common in the deserts of the southwestern US.
To a geologist, a block of ice is a rock, a mass of crystalline grains of the mineral ice. Like igneous rock, it is formed by the freezing of a fluid. Like sedimentary rock, it is formed from materials deposited in layers at Earth’s surface and can accumulate to great thicknesses. Like metamorphic rock, it is transformed by recrystallization under pressure.
A glacier starts with abundant winter snowfall that does not melt away in the summer. The snow is slowly converted into ice, and when the ice is thick enough, it begins to flow.
Basic ingredients: freezing cold and lots of snow.
Today, the engine of civilization runs primarily on fossil. Taken together, oil, natural gas, and coal account for 85% of global energy consumption.
Total wasted energy was 58.1 quads. Therefore, the efficiency of the US energy system was only about 39%.
Oil and gas begin to form in sedimentary basins where the production of organic matter is high and the supply of oxygen in the sediments is inadequate to decompose all the organic matter they contain. Many offshore thermal subsidence basins on continental margins satisfy both these conditions. In such environments, and to a lesser degree in some river deltas and inland seas, the rate of sedimentation is high, and organic matter is buried and protected from decomposition.
In the decade 2002-2012, the world consumed about 0.3% barrels of oil; yet, the worldwide reserves of oil did not decline; in fact, they increased from about 1.3T barrels to almost 1.7T barrels. Oil exploration is an immensely successful geologic activity.
The oil fields of the Middle East account for 48% of the world’s total.
There are huge resources of coal in sedimentary rocks. Although coal has been a major energy source since the late 19th century, only a few percent of the world’s coal reserves have been consumed. These reserves amount to 860B metric tons, which are capable of producing more energy than any other fossil fuel. About 85% of the world’s coal resources are concentrated in the former Soviet Union, China, and the US; these areas are also the world’s largest coal producers. The US has enough deposits to last for a few hundred years at the nation’s current rate of use.
The extraction and combustion of coal present serious problems that make it a less desirable fuel than oil and natural gas. Underground coal mining is a dangerous profession.
Coal is a notorious dirty fuel. When burned, it produces 25% more CO2 per unit of energy than oil and 70% more than natural gas; in other words, its carbon intensity is high. It also causes acid rain.
In 2012, 35% of Brazil’s automobile fuels came from sugarcane.
In the US, hydroelectric dams deliver less than 3% of the nation’s annual energy consumption. The US Department of Energy has identified more than 5K sites where new hydroelectric dams could be built and operated economically. Such expansion would be resisted, however, because the dams would drown farmlands and wilderness areas under artificial reservoirs while adding only a small amount of energy to the US supply.
A partial solution — and certainly the most economical one — is to improve energy use efficiency and reduce waste. In a real sense, using energy more efficiently is like discovering a new source of fuel.