The rocky side of a mountain creek near Orosí, Costa Rica. (presumably metamorphic rocks)
Earth science or geoscience includes all fields of natural science related to planetEarth. This is a branch of science dealing with the physical and chemical constitution of Earth and its atmosphere. Earth science can be considered to be a branch of planetary science, but with a much older history. Earth science encompasses four main branches of study, the lithosphere, the hydrosphere, the atmosphere, and the biosphere, each of which is further broken down into more specialized fields.
There are both reductionist and holistic approaches to Earth sciences. It is also the study of Earth and its neighbors in space. Some Earth scientists use their knowledge of the planet to locate and develop energy and mineral resources. Others study the impact of human activity on Earth's environment, and design methods to protect the planet. Some use their knowledge about Earth processes such as volcanoes, earthquakes, and hurricanes to plan communities that will not expose people to these dangerous events.
Earth sciences can include the study of geology, the lithosphere, and the large-scale structure of Earth's interior, as well as the atmosphere, hydrosphere, and biosphere. Typically, Earth scientists use tools from geology, chronology, physics, chemistry, geography, biology, and mathematics to build a quantitative understanding of how Earth works and evolves. Earth science affects our everyday lives. For example, meteorologists study the weather and watch for dangerous storms. Hydrologists examine water and warn of floods. Seismologists study earthquakes and try to understand where they will strike. Geologists study rocks and help to locate useful minerals. Earth scientists often work in the field—perhaps climbing mountains, exploring the seabed, crawling through caves, or wading in swamps. They measure and collect samples (such as rocks or river water), then record their findings on charts and maps.
Geochemistry is defined as the study of the processes that control the abundance, composition, and distribution of chemical compounds and isotopes in geologic environments. Geochemists use the tools and principles of chemistry to study the composition, structure, processes, and other physical aspects of the Earth. Major subdisciplines are aqueous geochemistry, cosmochemistry, isotope geochemistry and biogeochemistry.
Ecology covers the interactions between organisms and their environment. This field of study differentiates the study of Earth from the study of other planets in the Solar System, Earth being its only planet teeming with life.
Hydrology, oceanography and limnology are studies which focus on the movement, distribution, and quality of the water and involves all the components of the hydrologic cycle on the Earth and its atmosphere (or hydrosphere). "Sub-disciplines of hydrology include hydrometeorology, surface water hydrology, hydrogeology, watershed science, forest hydrology, and water chemistry."
Plate tectonics might be thought of as the process by which the Earth is resurfaced. As the result of seafloor spreading, new crust and lithosphere is created by the flow of magma from the mantle to the near surface, through fissures, where it cools and solidifies. Through subduction, oceanic crust and lithosphere returns to the convecting mantle.
Areas of the crust where new crust is created are called divergent boundaries, those where it is brought back into the Earth are convergent boundaries and those where plates slide past each other, but no new lithospheric material is created or destroyed, are referred to as transform (or conservative) boundariesEarthquakes result from the movement of the lithospheric plates, and they often occur near convergent boundaries where parts of the crust are forced into the earth as part of subduction.
Volcanoes result primarily from the melting of subducted crust material. Crust material that is forced into the asthenosphere melts, and some portion of the melted material becomes light enough to rise to the surface—giving birth to volcanoes.
The troposphere, stratosphere, mesosphere, thermosphere, and exosphere are the five layers which make up Earth's atmosphere. 75% of the gases in the atmosphere are located within the troposphere, the lowest layer. In all, the atmosphere is made up of about 78.0% nitrogen, 20.9% oxygen, and 0.92% argon. In addition to the nitrogen, oxygen, and argon there are small amounts of other gases including CO2 and water vapor. Water vapor and CO2 allow the Earth's atmosphere to catch and hold the Sun's energy through a phenomenon called the greenhouse effect. This allows Earth's surface to be warm enough to have liquid water and support life. In addition to storing heat, the atmosphere also protects living organisms by shielding the Earth's surface from cosmic rays—which are often incorrectly thought to be deflected by the magnetic field. The magnetic field—created by the internal motions of the core—produces the magnetosphere which protects Earth's atmosphere from the solar wind. As the Earth is 4.5 billion years old, it would have lost its atmosphere by now if there were no protective magnetosphere.
Methodologies vary depending on the nature of the subjects being studied. Studies typically fall into one of three categories: observational, experimental, or theoretical. Earth scientists often conduct sophisticated computer analysis or visit an interesting location to study earth phenomena (e.g. Antarctica or hot spot island chains).
A foundational idea in Earth science is the notion of uniformitarianism, which states that "ancient geologic features are interpreted by understanding active processes that are readily observed." In other words, any geologic processes at work in the present have operated in the same ways throughout geologic time. This enables those who study Earth's history to apply knowledge of how Earth processes operate in the present to gain insight into how the planet has evolved and changed throughout long history.
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