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Eutrophication can be a natural process and occurs naturally through the gradual accumulation of sediment and nutrients. Naturally, eutrophication is usually caused by the natural accumulation of nutrients from dissolved phosphate minerals and dead plant matter in water. [29] [30] Natural eutrophication has been well-characterized in lakes.
Palynodinium, a fossil species of dinoflagellate cyst, is used to demarcate the K/Pg boundary, which marks the terminal Cretaceous and the extinction of the dinosaurs. [ 111 ] Such reconstructions can be done via semi-quantitative techniques, such as ordination techniques, [ 47 ] which can indicate trends in environmental parameters.
Large collections of bird fossils representing a range of different species provide definitive evidence for the persistence of archaic birds to within 300,000 years of the K–Pg boundary. The absence of these birds in the Paleogene is evidence that a mass extinction of archaic birds took place there.
This further supports a volcanic cause of the Carnian pluvial episode. [44] Mercury spikes are also found alongside carbon cycle disruptions in both marine [ 45 ] and lake [ 46 ] sediments in China. These mercury spikes have no trace of mass-independent fractionation , meaning that their isotope distribution is most consistent with fallout from ...
Because the estimated date of the object's impact and the Cretaceous–Paleogene boundary (K–Pg boundary) coincide, there is now a scientific consensus that this impact was the Cretaceous–Paleogene extinction event which caused the death of most of the planet's non-avian dinosaurs and many other species.
Luis Walter Alvarez, left, and his son Walter, right, at the K–T Boundary in Gubbio, Italy, 1981. The Alvarez hypothesis posits that the mass extinction of the non-avian dinosaurs and many other living things during the Cretaceous–Paleogene extinction event was caused by the impact of a large asteroid on the Earth.
Aquatic and marine dead zones can be caused by an increase in nutrients (particularly nitrogen and phosphorus) in the water, known as eutrophication. These nutrients are the fundamental building blocks of single-celled, plant-like organisms that live in the water column, and whose growth is limited in part by the availability of these materials.
It is a primary cause of eutrophication of surface waters (lakes, rivers and coastal waters), in which excess nutrients, usually nitrogen or phosphorus, stimulate algal growth. [1] Sources of nutrient pollution include surface runoff from farm fields and pastures, discharges from septic tanks and feedlots , and emissions from combustion.