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An extinction event is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a sharp fall in the diversity and abundance of multicellular organisms. It occurs when the rate of extinction increases with respect to the background extinction rate and the rate of speciation. Estimates of the number of major mass extinctions in the last 540 million years range from as few as five to more than twenty. These differences stem from disagreement as to what constitutes a "major" extinction event, and the data chosen to measure past diversity.
The timeline of the evolutionary history of life represents the current scientific theory outlining the major events during the development of life on planet Earth. Dates in this article are consensus estimates based on scientific evidence, mainly fossils.
James Ephraim Lovelock was an English independent scientist, environmentalist and futurist. He is best known for proposing the Gaia hypothesis, which postulates that the Earth functions as a self-regulating system.
Paleontology, also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch. It includes the study of fossils to classify organisms and study their interactions with each other and their environments. Paleontological observations have been documented as far back as the 5th century BC. The science became established in the 18th century as a result of Georges Cuvier's work on comparative anatomy, and developed rapidly in the 19th century. The term has been used since 1822 formed from Greek παλαιός, ὄν, and λόγος.
The PaleozoicEra is the first of three geological eras of the Phanerozoic Eon. Beginning 538.8 million years ago (Ma), it succeeds the Neoproterozoic and ends 251.9 Ma at the start of the Mesozoic Era. The Paleozoic is subdivided into six geologic periods :
Approximately 251.9 million years ago, the Permian–Triassicextinction event forms the boundary between the Permian and Triassic geologic periods, and with them the Paleozoic and Mesozoic eras. It is the Earth's most severe known extinction event, with the extinction of 57% of biological families, 83% of genera, 81% of marine species and 70% of terrestrial vertebrate species. It is also the largest known mass extinction of insects. It is the largest of the "Big Five" mass extinctions of the Phanerozoic. There is evidence for one to three distinct pulses, or phases, of extinction.
The Silurian is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at 443.8 million years ago (Mya), to the beginning of the Devonian Period, 419.2 Mya. The Silurian is the shortest period of the Paleozoic Era. As with other geologic periods, the rock beds that define the period's start and end are well identified, but the exact dates are uncertain by a few million years. The base of the Silurian is set at a series of major Ordovician–Silurian extinction events when up to 60% of marine genera were wiped out.
The Gaia hypothesis, also known as the Gaia theory, Gaia paradigm, 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.
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. 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.
A geomagnetic reversal is a change in a planet's magnetic field such that the positions of magnetic north and magnetic south are interchanged. The Earth's field has alternated between periods of normal polarity, in which the predominant direction of the field was the same as the present direction, and reverse polarity, in which it was the opposite. These periods are called chrons.
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. Prior to 2013, it was commonly cited as having happened about 65 million years ago, but Renne and colleagues (2013) gave an updated value of 66 million years. Evidence indicates that the asteroid fell in the Yucatán Peninsula, at Chicxulub, Mexico. The hypothesis is named after the father-and-son team of scientists Luis and Walter Alvarez, who first suggested it in 1980. Shortly afterwards, and independently, the same was suggested by Dutch paleontologist Jan Smit.
The Early Triassic is the first of three epochs of the Triassic Period of the geologic timescale. It spans the time between 251.9 Ma and 247.2 Ma. Rocks from this epoch are collectively known as the Lower Triassic Series, which is a unit in chronostratigraphy.
The history of life on Earth traces the processes by which living and fossil organisms evolved, from the earliest emergence of life to present day. Earth formed about 4.5 billion years ago and evidence suggests that life emerged prior to 3.7 Ga. Although there is some evidence of life as early as 4.1 to 4.28 Ga, it remains controversial due to the possible non-biological formation of the purported fossils.
The Cretaceous–Paleogene (K–Pg) boundary, formerly known as the Cretaceous–Tertiary (K–T) boundary, is a geological signature, usually a thin band of rock containing much more iridium than other bands. The K–Pg boundary marks the end of the Cretaceous Period, the last period of the Mesozoic Era, and marks the beginning of the Paleogene Period, the first period of the Cenozoic Era. Its age is usually estimated at 66 million years, with radiometric dating yielding a more precise age of 66.043 ± 0.011 Ma.
The CLAW hypothesis proposes a negative feedback loop that operates between ocean ecosystems and the Earth's climate. The hypothesis specifically proposes that particular phytoplankton that produce dimethyl sulfide are responsive to variations in climate forcing, and that these responses act to stabilise the temperature of the Earth's atmosphere. The CLAW hypothesis was originally proposed by Robert Jay Charlson, James Lovelock, Meinrat Andreae and Stephen G. Warren, and takes its acronym from the first letter of their surnames.
The Medea hypothesis is a term coined by paleontologist Peter Ward for a hypothesis that contests the Gaian hypothesis and proposes that multicellular life, understood as a superorganism, may be self-destructive or suicidal. The metaphor refers to the mythological Medea, who kills her own children.
Gregory John Retallack is an Australian paleontologist, geologist, and author who specializes in the study of fossil soils (paleopedology). His research has examined the fossil record of soils though major events in Earth history, extending back some 4.6 billion years. Among his publications he has written two standard paleopedology textbooks, said N. Jones in Nature Geoscience "Retallack has literally written the book on ancient soils."
The Cretaceous–Paleogene (K–Pg) extinction event, also known as the Cretaceous–Tertiary(K–T)extinction, was a sudden mass extinction of three-quarters of the plant and animal species on Earth, approximately 66 million years ago. The event caused the extinction of all non-avian dinosaurs. Most other tetrapods weighing more than 25 kilograms also became extinct, with the exception of some ectothermic species such as sea turtles and crocodilians. It marked the end of the Cretaceous period, and with it the Mesozoic era, while heralding the beginning of the Cenozoic era, which continues to this day.
Since the 19th century, a significant amount of research has been conducted on the Cretaceous–Paleogene extinction event, the mass extinction that ended the dinosaur-dominated Mesozoic Era and set the stage for the Age of Mammals, or Cenozoic Era. A chronology of this research is presented here.
Conservation paleobiology is a field of paleontology that applies the knowledge of the geological and paleoecological record to the conservation and restoration of biodiversity and ecosystem services. Despite the influence of paleontology on ecological sciences can be traced back at least at the 18th century, the current field has been established by the work of K.W. Flessa and G.P. Dietl in the first decade of the 21st century. The discipline utilizes paleontological and geological data to understand how biotas respond to climate and other natural and anthropogenic environmental change. These information are then used to address the challenges faced by modern conservation biology, like understanding the extinction risk of endangered species, providing baselines for restoration and modelling future scenarios for species range's contraction or expansion.
References
- ↑ "Central Sierra Field Research Stations". sagehen.ucnrs.org. Archived from the original on 18 July 2011. Retrieved 12 January 2022.
- ↑ "Keck funds project to track life cycle of water"; Sanders, Robert, Media Relations; February 23, 2006; Retrieved on 2007-01-19
- ↑ Kirchner, J.W., A. Weil (2000). "Delayed biological recovery from extinctions throughout the fossil record". Nature . 404 (6774): 177–180. Bibcode:2000Natur.404..177K. doi:10.1038/35004564. PMID 10724168. S2CID 4428714.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ↑ Carol Kaesuk Yoon (2000-03-09). "Study Jolts Views on Recovery From Extinctions". The New York Times . Retrieved 2008-04-12.
- ↑ JAMES W. KIRCHNER (2002). "THE GAIA HYPOTHESIS: FACT, THEORY, AND WISHFUL THINKING" (PDF). Climatic Change . 451 (4): 391–408. doi:10.1023/A:1014237331082. S2CID 15776141. Archived from the original (PDF) on 2018-07-08.
