Nature of human effects

The human impact on biodiversity forms one of the primary attributes of the Anthropocene. Humankind has entered what is sometimes called the Earth's sixth major extinction.Scientists Build Case for 'Sixth Extinction' ... and Say It Could Kill Us Most experts agree that human activities have accelerated the rate of species extinction. The exact rate remains controversial – perhaps 100 to 1000 times the normal background rate of extinction.[ ] A 2010 study found that "marine phytoplankton – the vast range of tiny algae species accounting for roughly half of Earth's total photosynthetic biomass – had declined substantially in the world's oceans over the past century. From 1950 alone, algal biomass decreased by around 40%, probably in response to ocean warming (Global Warming) – and that the decline had gathered pace in recent years.Ocean greenery under warming stress Some authors have postulated that without human impacts the biodiversity of the planet would continue to grow at an exponential rate.<ref name="SahneyBentonFerry2010LinksDiversityVertebrates"/> – implying that human activities accelerate or exacerbate global warming.

Increases in global rates of extinction have been elevated above background rates since at least 1500, and appear to have accelerated in the 19th century and further since.<ref name="Science2016" /> A 13 July 2012 ''New York Times (The New York Times)'' op-ed by ecologist Roger Bradbury predicted the end of biodiversity for the oceans, labelling coral reefs doomed: "Coral reefs will be the first, but certainly not the last, major ecosystem to succumb to the Anthropocene."A World Without Coral Reefs This op-ed quickly generated much discussion among conservationists; The Nature Conservancy rebutted Bradbury on its website, defending its position of protecting coral reefs despite continued human impacts causing reef declines.Coral Reefs: The Living Dead, Or A Comeback Kid?

In a pair of studies published in 2015, extrapolation from observed extinction of Hawaiian snails led to the conclusion that "the biodiversity crisis is real", and that 7% of all species on Earth may have disappeared already.Research shows catastrophic invertebrate extinction in Hawai'i and globally [ Mass extinction in poorly known taxa] Human predation was noted as being unique in the history of life on Earth as being a globally distributed 'superpredator', with predation of the adults of other apex predators and with widespread impacts on food webs worldwide.[ ] A study published in May 2017 in ''Proceedings of the National Academy of Sciences (Proceedings of the National Academy of Sciences of the United States of America)'' posited that a “biological annihilation” akin to a sixth mass extinction event is underway as a result of anthropogenic causes, such as human overpopulation, continued population growth and overconsumption, particularly by the wealthy. The study suggested that as much as 50% of the number of animal individuals that once lived on Earth were already extinct, threatening the basis for human existence too.Biological annihilation via the ongoing sixth mass extinction signaled by vertebrate population losses and declines Sixth mass extinction: The era of 'biological annihilation'

Permanent changes in the distribution of organisms from human influence will become identifiable in the geologic record. Researchers have documented the movement of many species into regions formerly too cold for them, often at rates faster than initially expected.[ ] This has occurred in part as a result of changing climate, but also in response to farming and fishing, and to the accidental introduction of non-native species to new areas through global travel.<ref name="Science2016" /> The ecosystem of the entire Black Sea may have changed during the last 2000 years as a result of nutrient- and silica-input from eroding deforested lands along the Danube River.

One geological symptom resulting from human activity is increasing atmospheric (Earth's atmosphere) carbon dioxide (CO₂) content. During the glacial–interglacial (ice age) cycles of the past million years, natural processes have varied CO₂ by approximately 100 ppm (Parts per million) (from 180 ppm to 280 ppm). , anthropogenic net emissions of CO₂ increased atmospheric concentration by a comparable amount from 280 ppm (Holocene or pre-industrial "equilibrium") to approximately 400 ppm,ESRL Global Monitoring Division - Global Greenhouse Gas Reference Network with 2015&ndash;16 monthly monitoring data of CO₂ displaying a rising trend above 400 ppm.NASA Global Climate Change - Vital Signs of the Planet - Facts - Carbon Dioxide This signal in the Earth's climate system is especially significant because it is occurring much faster,BBC NEWS - Science/Nature - Deep ice tells long climate story and to a greater extent, than previous, similar changes. Most of this increase is due to the combustion of fossil fuels such as coal, oil (Petroleum), and gas (Natural gas), although smaller fractions are the result of cement production and land-use changes (e.g. deforestation).

Changes in drainage patterns traceable to human activity will persist over geologic time in large parts of the continents where the geologic regime is erosional. This includes the paths of roads and highways defined by their grading and drainage control. Direct changes to the form of the Earth's surface by human activities (e.g., quarrying, landscaping) also record human impacts.

It has been suggested the deposition of calthemite formations are one example of a natural process which has not previously occurred prior to the human modification of the Earth's surface, and therefore represents a unique process of the Anthropocene.Ozymandias in the Anthropocene: the city as an emerging landform Calthemite is a secondary deposit, derived from concrete, lime (Lime (material)), mortar (Mortar (masonry)) or other calcareous material ''outside the cave environment''. Calthemites grow on or under, man-made structures (including mines and tunnels) and mimic the shapes and forms of cave speleothems, such as stalactites, stalagmites, flowstone etc.

Human activities like deforestation and road construction are believed to have elevated average total sediment fluxes across the Earth's surface.<ref name="Science2016" /> However, construction of dams on many rivers around the world means the rates of sediment deposition in any given place do not always appear to increase in the Anthropocene. For instance, many river deltas around the world are actually currently starved of sediment by such dams, and are subsiding and failing to keep up with sea level rise, rather than growing.<ref name="Science2016" />

Increases in erosion due to farming and other operations will be reflected by changes in sediment composition and increases in deposition rates elsewhere. In land areas with a depositional regime, engineered structures will tend to be buried and preserved, along with litter and debris. Litter and debris thrown from boats or carried by rivers and creeks will accumulate in the marine environment, particularly in coastal areas. Such manmade artifacts preserved in stratigraphy are known as "technofossils".<ref name="Science2016" />

Changes in biodiversity will also be reflected in the fossil record, as will species introductions. An example cited is the domestic chicken, originally the red junglefowl ''Gallus gallus'', native to south-east Asia but has since become the world's most common bird through human breeding and consumption, with over 60 billion consumed a year and whose bones would become fossilized in landfill sites.How the domestic chicken rose to define the Anthropocene

In terms of trace elements, there are distinct signatures left by modern societies. For example, in the Upper Fremont Glacier in Wyoming, there is a layer of chlorine present in ice cores from 1960s atomic weapon testing programs, as well as a layer of mercury (mercury (element)) associated with coal plants in the 1980s. From 1945 to 1951, nuclear fallout is found locally around atomic device test sites, whereas from 1952 to 1980, tests of thermonuclear devices have left a clear, global signal of excess ¹⁴C, ²³⁹Pu, and other artificial radionuclides. The highest concentration of radionuclides was in 1964, one of the dates which has been proposed as a possible benchmark for the start of the formally defined Anthropocene.The Anthropocene is functionally and stratigraphically distinct from the Holocene

Human burning of fossil fuels has also left distinctly elevated concentrations of black carbon, inorganic ash, and spherical carbonaceous particles in recent sediments across the world. Concentrations of these components increases markedly and almost simultaneously around the world beginning around 1950.<ref name="Science2016" />