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 the planet Earth. This is a branch of science dealing with the physical and chemical constitution of the 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.

The Earth sciences can include the study of geology, the lithosphere, and the large-scale structure of the 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 the Earth works and evolves. Earth science affects our everyday lives. For example, meteorologists study the weather and watch for dangerous storms. Hydrologists study 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 they record their findings on charts and maps.

An ecological analysis of CO
₂ in an ecosystem. As systems biology, systems ecology seeks a holistic view of the interactions and transactions within and between biological and ecological systems.

Earth system science (ESS) is the application of systems science to the Earth.^[1][2][3][4] In particular, it considers interactions and 'feedbacks', through material and energy fluxes, between the Earth's sub-systems' cycles, processes and "spheres"—atmosphere, hydrosphere, cryosphere,^[5] geosphere, pedosphere, lithosphere, biosphere,^[6] and even the magnetosphere^[4]—as well as the impact of human societies on these components.^[7] At its broadest scale, Earth system science brings together researchers across both the natural and social sciences, from fields including ecology, economics, geography, geology, glaciology, meteorology, oceanography, climatology, paleontology, sociology, and space science.^[8] Like the broader subject of systems science, Earth system science assumes a holistic view of the dynamic interaction between the Earth's spheres and their many constituent subsystems fluxes and processes, the resulting spatial organization and time evolution of these systems, and their variability, stability and instability.^[9][10][11] Subsets of Earth System science include systems geology^[10][12] and systems ecology,^[13] and many aspects of Earth System science are fundamental to the subjects of physical geography^[10][14] and climate science.^[15]

The study of planetary habitability is partly based upon extrapolation from knowledge of the Earth's conditions, as the Earth is the only planet currently known to harbour life.

The Gaia hypothesis (/ˈɡaɪ.ə/, /ˈɡeɪ.ə/, /ˈɡaɪˈʌ/), also known as the Gaia theory or the Gaia principle, proposes that living organisms interact with their inorganic surroundings on Earth to form a synergistic and self-regulating, complex system that helps to maintain and perpetuate the conditions for life on the planet.

The hypothesis was formulated by the chemist James Lovelock^[1] and co-developed by the microbiologist Lynn Margulis in the 1970s.^[2] Lovelock named the idea after Gaia, the primordial goddess who personified the Earth in Greek mythology. In 2006, the Geological Society of London awarded Lovelock the Wollaston Medal in part for his work on the Gaia hypothesis.^[3]

Topics related to the hypothesis include how the biosphere and the evolution of organisms affect the stability of global temperature, salinity of seawater, atmospheric oxygen levels, the maintenance of a hydrosphere of liquid water and other environmental variables that affect the habitability of Earth.

The Gaia hypothesis was initially criticized for being teleological and against the principles of natural selection, but later refinements aligned the Gaia hypothesis with ideas from fields such as Earth system science, biogeochemistry and systems ecology.^[4][5][6] Lovelock also once described the "geophysiology" of the Earth.^{[7][further explanation needed]} Even so, the Gaia hypothesis continues to attract criticism, and today some scientists consider it to be only weakly supported by, or at odds with, the available evidence.^[8][9][10]

The colorful microbial mats of Grand Prismatic Spring in Yellowstone National Park, USA. The orange mats are composed of Chloroflexi, Cyanobacteria, and other organisms that thrive in the 70˚C water. Geobiologists often study extreme environments like this because they are home to extremophilic organisms. It has been hypothesized that these environments may be representative of early Earth.^[1]

Geobiology is a field of scientific research that explores the interactions between the physical Earth and the biosphere. It is a relatively young field, and its borders are fluid. There is considerable overlap with the fields of ecology, evolutionary biology, microbiology, paleontology, and particularly soil science and biogeochemistry. Geobiology applies the principles and methods of biology, geology, and soil science to the study of the ancient history of the co-evolution of life and Earth as well as the role of life in the modern world.^[2] Geobiologic studies tend to be focused on microorganisms, and on the role that life plays in altering the chemical and physical environment of the pedosphere, which exists at the intersection of the lithosphere, atmosphere, hydrosphere and/or cryosphere. It differs from biogeochemistry in that the focus is on processes and organisms over space and time rather than on global chemical cycles.

Geobiological research synthesizes the geologic record with modern biologic studies. It deals with process - how organisms affect the Earth and vice versa - as well as history - how the Earth and life have changed together. Much research is grounded in the search for fundamental understanding, but geobiology can also be applied, as in the case of microbes that clean up oil spills.^[3]

Geobiology employs molecular biology, environmental microbiology, chemical analyses, and the geologic record to investigate the evolutionary interconnectedness of life and Earth. It attempts to understand how the Earth has changed since the origin of life and what it might have been like along the way. Some definitions of geobiology even push the boundaries of this time frame - to understanding the origin of life and to the role that man has played and will continue to play in shaping the Earth in the Anthropocene.^[4]

Planetary boundaries diagram of 2009.

Planetary boundaries is a concept involving Earth system processes that contain environmental boundaries. It was proposed in 2009 by a group of Earth system and environmental scientists, led by Johan Rockström from the Stockholm Resilience Centre and Will Steffen from the Australian National University. The group wanted to define a "safe operating space for humanity" for the international community, including governments at all levels, international organizations, civil society, the scientific community and the private sector, as a precondition for sustainable development. The framework is based on scientific evidence that human actions since the Industrial Revolution have become the main driver of global environmental change.

According to the paradigm, "transgressing one or more planetary boundaries may be deleterious or even catastrophic due to the risk of crossing thresholds that will trigger non-linear, abrupt environmental change within continental- to planetary-scale systems."^[1] The Earth system process boundaries mark the safe zone for the planet to the extent that they are not crossed. As of 2009, two boundaries have already been crossed, while others are in imminent danger of being crossed.^[2][3]

Movement of carbon between land, atmosphere, and ocean in billions of tons per year. Yellow numbers are natural fluxes, red are human contributions, white are stored carbon. The effects of volcanic and tectonic activity are not included.^[1]

The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth. Carbon is the main component of biological compounds as well as a major component of many minerals such as limestone. Along with the nitrogen cycle and the water cycle, the carbon cycle comprises a sequence of events that are key to make Earth capable of sustaining life. It describes the movement of carbon as it is recycled and reused throughout the biosphere, as well as long-term processes of carbon sequestration to and release from carbon sinks.

The carbon cycle was discovered by Joseph Priestley and Antoine Lavoisier, and popularized by Humphry Davy.^[2]

World map of countries by their raw ecological footprint, relative to the world average biocapacity (2007).

National ecological surplus or deficit, measured as a country's biocapacity per person (in global hectares) minus its ecological footprint per person (also in global hectares). Data from 2013.^[1]

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The ecological footprint is a method promoted by the Global Footprint Network to measure human demand on natural capital, i.e. the quantity of nature it takes to support people or an economy.^[2][3][4] It tracks this demand through an ecological accounting system. The accounts contrast the biologically productive area people use for their consumption to the biologically productive area available within a region or the world (biocapacity, the productive area that can regenerate what people demand from nature). In short, it is a measure of human impact on the environment.

Footprint and biocapacity can be compared at the individual, regional, national or global scale. Both footprint and biocapacity change every year with number of people, per person consumption, efficiency of production, and productivity of ecosystems. At a global scale, footprint assessments show how big humanity's demand is compared to what Earth can renew. Global Footprint Network estimates that, as of 2014, humanity has been using natural capital 1.7 times as fast as Earth can renew it, which they describe as meaning humanity's ecological footprint corresponds to 1.7 planet Earths.^[5][6]

Ecological footprint analysis is widely used around the world in support of sustainability assessments.^[7] It enables people to measure and manage the use of resources throughout the economy and explore the sustainability of individual lifestyles, goods and services, organizations, industry sectors, neighborhoods, cities, regions and nations.^[8]

The Anthropocene (/ænˈθrɒp.əˌsiːn, -ˈθrɒp.oʊ-/ ann-THROP-ə-seen, -⁠THROP-oh-)^[1] is a proposed geological epoch dating from the commencement of significant human impact on Earth's geology and ecosystems, including, but not limited to, anthropogenic climate change.^{[2][3][4][5][6]}

As of July 2020^[update], neither the International Commission on Stratigraphy (ICS) nor the International Union of Geological Sciences (IUGS) has officially approved the term as a recognised subdivision of geologic time,^[4][7][8] although the Anthropocene Working Group (AWG) of the Subcommission on Quaternary Stratigraphy (SQS) of the ICS voted in April 2016 to proceed towards a formal golden spike (GSSP) proposal to define the Anthropocene epoch in the geologic time scale and presented the recommendation to the International Geological Congress in August 2016.^[9] In May 2019, the AWG voted in favour of submitting a formal proposal to the ICS by 2021,^[10] locating potential stratigraphic markers to the mid-twentieth century of the common era.^[11][10][12] This time period coincides with the Great Acceleration, a post-WWII time during which socioeconomic and Earth system trends started increasing dramatically,^[13] and the Atomic Age.

Various start dates for the Anthropocene have been proposed, ranging from the beginning of the Agricultural Revolution 12,000–15,000 years ago, to as recent as the 1960s. The ratification process is still ongoing, and thus a date remains to be decided definitively, but the peak in radionuclides fallout consequential to atomic bomb testing during the 1950s has been more favoured than others, locating a possible beginning of the Anthropocene to the detonation of the first atomic bomb in 1945, or the Partial Nuclear Test Ban Treaty in 1963.^[10]

Artist's impression of a major asteroid impact. An asteroid with an impact strength of a billion atomic bombs may have caused the extinction of the dinosaurs.^[1]

A global catastrophic risk is a hypothetical future event which could damage human well-being on a global scale,^[2] even endangering or destroying modern civilization.^[3] An event that could cause human extinction or permanently and drastically curtail humanity's potential is known as an existential risk.^[4]

Potential global catastrophic risks include anthropogenic risks, caused by humans (technology, governance, climate change), and non-anthropogenic or external risks.^[5] Examples of technology risks are hostile artificial intelligence and destructive biotechnology or nanotechnology. Insufficient or malign global governance creates risks in the social and political domain, such as a global war, including nuclear holocaust, bioterrorism using genetically modified organisms, cyberterrorism destroying critical infrastructure like the electrical grid; or the failure to manage a natural pandemic. Problems and risks in the domain of earth system governance include global warming, environmental degradation, including extinction of species, famine as a result of non-equitable resource distribution, human overpopulation, crop failures and non-sustainable agriculture.

Examples of non-anthropogenic risks are an asteroid impact event, a supervolcanic eruption, a lethal gamma-ray burst, a geomagnetic storm destroying electronic equipment, natural long-term climate change, hostile extraterrestrial life, or the predictable Sun transforming into a red giant star engulfing the Earth.

This clock representation shows some of the major units of geological time and definitive events of Earth history. The Hadean eon represents the time before fossil record of life on Earth; its upper boundary is now regarded as 4.0 Ga (billion years ago).^[1] Other subdivisions reflect the evolution of life; the Archean and Proterozoic are both eons, the Palaeozoic, Mesozoic and Cenozoic are eras of the Phanerozoic eon. The three million year Quaternary period, the time of recognizable humans, is too small to be visible at this scale.

The geologic time scale (GTS) is a system of chronological dating that classifies geological strata (stratigraphy) in time. It is used by geologists, paleontologists, and other Earth scientists to describe the timing and relationships of events in geologic history. The time scale was developed through the study of physical rock layers and relationships as well as the times when different organisms appeared, evolved and became extinct through the study of fossilized remains and imprints. The table of geologic time spans, presented here, agrees with the nomenclature, dates and standard color codes set forth by the International Commission on Stratigraphy (ICS).

An illustration of the oceanic whale pump showing how whales cycle nutrients through the water column

In ecology and Earth science, a biogeochemical cycle or substance turnover or cycling of substances is a pathway by which a chemical substance moves through biotic (biosphere) and abiotic (lithosphere, atmosphere, and hydrosphere) compartments of Earth. There are biogeochemical cycles for the chemical elements calcium, carbon, hydrogen, mercury, nitrogen, oxygen, phosphorus, selenium, and sulfur; molecular cycles for water and silica; macroscopic cycles such as the rock cycle; as well as human-induced cycles for synthetic compounds such as polychlorinated biphenyl (PCB). In some cycles there are reservoirs where a substance remains for a long period of time (such as an ocean or lake for water).

The greenhouse effect of solar radiation on the Earth's surface caused by greenhouse gases

Radiative forcing of different contributors to climate change in 2011, as reported in the fifth IPCC assessment report.

A greenhouse gas (sometimes abbreviated GHG) is a gas that absorbs and emits radiant energy within the thermal infrared range. Greenhouse gases cause the greenhouse effect^[1] on planets. The primary greenhouse gases in Earth's atmosphere are water vapor (H
2O), carbon dioxide (CO
2), methane (CH
4), nitrous oxide (N
2O), and ozone (O₃). Without greenhouse gases, the average temperature of Earth's surface would be about −18 °C (0 °F),^[2] rather than the present average of 15 °C (59 °F).^[3][4][5] The atmospheres of Venus, Mars and Titan also contain greenhouse gases.

Human activities since the beginning of the Industrial Revolution (around 1750) have produced a 45% increase in the atmospheric concentration of carbon dioxide, from 280 ppm in 1750 to 415 ppm in 2019.^[6] The last time the atmospheric concentration of carbon dioxide was this high was over 3 million years ago.^[4] This increase has occurred despite the uptake of more than half of the emissions by various natural "sinks" involved in the carbon cycle.^[7][8]

The vast majority of anthropogenic carbon dioxide emissions come from combustion of fossil fuels, principally coal, petroleum (including oil) and natural gas, with additional contributions coming from deforestation and other changes in land use.^[9][10] The leading source of anthropogenic methane emissions is agriculture, closely followed by gas venting and fugitive emissions from the fossil-fuel industry.^[11][10] Traditional rice cultivation is the second biggest agricultural methane source after livestock, with a near-term warming impact equivalent to the carbon-dioxide emissions from all aviation.^[12]

At current emission rates, temperatures could increase by 2 °C (3.6°F), which the United Nations' Intergovernmental Panel on Climate Change (IPCC) designated as the upper limit to avoid "dangerous" levels, by 2036.^[13]

Human impact on the environment or anthropogenic impact on the environment includes changes to biophysical environments^[1] and ecosystems, biodiversity, and natural resources^[2][3] caused directly or indirectly by humans, including global warming,^[4][5] environmental degradation^[6] (such as ocean acidification^[4][7]), mass extinction and biodiversity loss,^{[8][9][10][11]} ecological crisis, and ecological collapse. Modifying the environment to fit the needs of society is causing severe effects, which become worse as the problem of human overpopulation continues.^[10][12] Some human activities that cause damage (either directly or indirectly) to the environment on a global scale include population growth,^[13][10] overconsumption, overexploitation, pollution, and deforestation, to name but a few. Some of the problems, including global warming and biodiversity loss pose an existential risk to the human race,^[14][15] and human overpopulation causes those problems.^[16][17]

The term anthropogenic designates an effect or object resulting from human activity. The term was first used in the technical sense by Russian geologist Alexey Pavlov, and it was first used in English by British ecologist Arthur Tansley in reference to human influences on climax plant communities.^[4] The atmospheric scientist Paul Crutzen introduced the term "Anthropocene" in the mid-1970s.^[18] The term is sometimes used in the context of pollution emissions that are produced from human activity since the start of the Agricultural Revolution but also applies broadly to all major human impacts on the environment.^[19] Many of the actions taken by humans that contribute to a heated environment stem from the burning of fossil fuel from a variety of sources, such as: electricity, cars, planes, space heating, manufacturing, or the destruction of forests.^[20]

Climate engineering or climate intervention,^[1] commonly referred to as geoengineering, is the deliberate and large-scale intervention in the Earth's climate system, usually with the aim of mitigating the adverse effects of global warming.^[2][3][4] The most prominent subcategories of climate engineering are solar radiation management and carbon dioxide removal. Solar radiation management refers to offsetting the warming effect of greenhouse gases by reflecting more solar radiation (sunlight) back into space. Carbon dioxide removal refers to removing carbon dioxide gas (CO
2) from the atmosphere and sequestering it for long periods of time.

Almost all research into solar radiation management has to date consisted of computer modelling or laboratory tests.^[5] A 2014 paper in Nature found that among a variety of climate engineering subcategories including three carbon dioxide removal techniques (afforestation, ocean iron fertilization, and ocean alkalinization), as well as ocean upwelling, only solar radiation management was able to return global average temperatures to pre-industrial levels.^[6]

Climate engineering approaches are sometimes viewed as potential options for limiting climate change or its impacts, alongside mitigation and adaptation.^[7][8] There is substantial agreement among scientists that climate engineering cannot substitute for climate change mitigation (reducing greenhouse gas emissions). Some approaches might be used as accompanying measures to sharp cuts in greenhouse gas emissions.^[1] Given that all types of measures for addressing climate change have economic, political, or physical limitations,^[9][10] some climate engineering approaches might eventually be used as part of an ensemble of measures, which can be referred to as climate restoration.^[11] Research on costs, benefits, and various types of risks of most climate engineering approaches is at an early stage and their understanding needs to improve to judge their adequacy and feasibility.^[12]

Most experts and major reports advise against relying on climate engineering techniques as a main solution to global warming, in part due to the large uncertainties over effectiveness and side effects and unforeseen consequences. However, most experts also argue that the risks of such interventions must be seen in the context of risks of dangerous global warming.^[13][14] Interventions at large scale may run a greater risk of disrupting natural systems resulting in a dilemma that those approaches that could prove highly (cost-)effective in addressing extreme climate risk, might themselves cause substantial risk.^[15] Some^[who?] have suggested that the concept of engineering the climate presents a moral hazard because it could reduce political and public pressure for emissions reduction, which could exacerbate overall climate risks; others assert that the threat of climate engineering could spur emissions cuts.^[16][17][18] Major academic institutions, including Harvard University, have begun research into solar radiation management, viewing it as a potential supplement to, rather than a replacement for, reducing emissions (mitigation).^[19]

Achieving sustainability will enable the Earth to continue supporting life.

Banaue rice terraces in the Philippines, a UNESCO World Heritage site.

Sustainability is the ability to exist constantly. In the 21st century, it refers generally to the capacity for the biosphere and human civilization to co-exist. It is also defined as the process of people maintaining change in a homeostasis balanced environment, in which the exploitation of resources, the direction of investments, the orientation of technological development and institutional change are all in harmony and enhance both current and future potential to meet human needs and aspirations.^[1] For many in the field, sustainability is defined through the following interconnected domains or pillars: environment, economic and social,^[2] which according to Fritjof Capra^[3] is based on the principles of Systems Thinking. Sub-domains of sustainable development have been considered also: cultural, technological and political.^[4][5] According to Our Common Future, sustainable development is defined as development that "meets the needs of the present without compromising the ability of future generations to meet their own needs."^[6][4] Sustainable development may be the organizing principle of sustainability, yet others may view the two terms as paradoxical (i.e., development is inherently unsustainable).^[7][8][9]

Sustainability can also be defined as a socio-ecological process characterized by the pursuit of a common ideal.^{[10][11][self-published source?]} An ideal is by definition unattainable in a given time and space. However, by persistently and dynamically approaching it, the process results in a sustainable system.^[10] Many environmentalists and ecologists argue that sustainability is achieved through the balance of species and the resources within their environment. As is typically practiced in natural resource management, the goal is to maintain this equilibrium, available resources must not be depleted faster than resources are naturally generated.

Modern use of the term sustainability is broad and difficult to define precisely.^[12] Originally, sustainability meant making only such use of natural, renewable resources that people can continue to rely on their yields in the long term.^[13] The concept of sustainability, or Nachhaltigkeit in German, can be traced back to Hans Carl von Carlowitz (1645–1714), and was applied to forestry.^[10]

Healthy ecosystems and environments are necessary to the survival of humans and other organisms. Ways of reducing negative human impact are environmentally-friendly chemical engineering, environmental resources management and environmental protection. Information is gained from green computing, green chemistry, earth science, environmental science and conservation biology. Ecological economics studies the fields of academic research that aim to address human economies and natural ecosystems.^[14]

Moving towards sustainability is also a social challenge that entails international and national law, urban planning and transport, supply chain management, local and individual lifestyles and ethical consumerism. Ways of living more sustainably can take many forms from reorganizing living conditions (e.g., ecovillages, eco-municipalities and sustainable cities), reappraising economic sectors (permaculture, green building, sustainable agriculture), or work practices (sustainable architecture), using science to develop new technologies (green technologies, renewable energy and sustainable fission and fusion power), or designing systems in a flexible and reversible manner,^[15][16] and adjusting individual lifestyles that conserve natural resources.^[17]

In sum, "the term 'sustainability' should be viewed as humanity's target goal of human-ecosystem equilibrium (homeostasis), while 'sustainable development' refers to the holistic approach and temporal processes that lead us to the end point of sustainability."^[4] Despite the increased popularity of the use of the term "sustainability," the possibility that human societies will achieve environmental sustainability has been, and continues to be, questioned—in light of environmental degradation, climate change, overconsumption, population growth and societies' pursuit of unlimited economic growth in a closed system.^[18][19]

Graph showing world phosphate rock production, 1900–2016, reported by US Geological Survey^[1]

Peak phosphorus is a concept to describe the point in time when humanity reaches the maximum global production rate of phosphorus as an industrial and commercial raw material. The term is used in an equivalent way to the better-known term peak oil.^[2] The issue was raised as a debate on whether a "peak phosphorus" was imminent or not around 2010, but was largely dismissed after USGS and other organizations increased the world estimates on available phosphorus resources.^[3]

Phosphorus is a finite (limited) resource that is widespread in the Earth's crust and in living organisms but is relatively scarce in concentrated forms, which are not evenly distributed across the Earth. The only cost-effective production method to date is the mining of phosphate rock, but only a few countries have significant reserves of it. The top four are Morocco, China, Algeria and Syria. Estimates for future production vary significantly depending on modelling and assumptions on extractable volumes, but it is inescapable that future production of phosphate rock will be heavily influenced by Morocco in the foreseeable future.^[4]

Means of commercial phosphorus production besides mining are few because the phosphorus cycle does not include significant gas-phase transport. ^[5] The predominant source of phosphorus in modern times is phosphate rock (as opposed to the guano that preceded it). According to some researchers, Earth's commercial and affordable phosphorus reserves are expected to be depleted in 50–100 years and peak phosphorus to be reached in approximately 2030.^[2][6] Others suggest that supplies will last for several hundreds of years.^[7] As with the timing of peak oil, the question is not settled, and researchers in different fields regularly publish different estimates of the rock phosphate reserves.^[8]