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Query: When was the Hadean era?
The Hadean (/ˈheɪdiən/) is a geologic eon of the Earth pre-dating the Archean. It began with the formation of the Earth about 4.6billion years ago and ended, as defined by the ICS, 4billion years ago.[1] As of 2016, the ICS describes its status as "informal".[2] Geologist Preston Cloud coined the term in 1972, originally to label the period before the earliest-known rocks on Earth.[3][4] W. Brian Harland later coined an almost synonymous term, the "Priscoan period", from priscus, the Latin word for "ancient".[5] Other, older texts simply refer to the eon as the Pre-Archean.
Hadean zircon is the oldest-surviving crustal material from the Earth's earliest geological time period, the Hadean eon, about 4 billion years ago. Zircon is a mineral that is commonly used for radiometric dating because it is highly resistant to chemical changes and appears in the form of small crystals or grains in most igneous and metamorphic host rocks.
The Zirconian is the second Era within the Hadean Eon in a proposed revision of the Precambrian time scale. It lasted 373 million years from the end of the Chaotian Era to the beginning of Eoarchean Era . The Zirconian follows the Chaotian Era and its beginning is chronometrically set at 4.404 ± 0.008 Gya. This corresponds to the age of the first occurrence of Hadean zircons in the Jack Hills in Western Australia (Yilgarn craton). The end of the Zirconian Era and the transition to the Acastan Period (the earliest period of the Archean Eon and Eoarchean Era) occurred with the appearance of the oldest rock at 4.031 ± 0.003 Gya.
In the Hadean, Archean, and early Proterozoic eras of Earth's history, the chemistry of erupted magmas was significantly different from today's, due to immature crustal and asthenosphere differentiation. These ultramafic volcanic rocks, with silica (SiO) contents below 45% are usually classified as komatiites.
Titanium in zircon geothermometry has so far been used in igneous rocks to estimate cooling temperatures of magma from zircon crystals dated to the Hadean age (>4.0 Ga). Low crystallization temperatures from zircons of this age suggests the Hadean Earth contained liquid water, which reduced the cooling temperature of crustal materials. Potentially, Ti-in-zircon thermometry of Earth's oldest zircons can show the progressive heat loss from a magmatic Hadean Earth to the onset of plate tectonics as the planet's crust began to cool and underwent plastic deformation. This will provide previously unknown evidence for the conditions in early Earth and allow testing of ideas of how the planet evolved through the Hadean and Archean eons.
Since few geological traces of this eon remain on Earth, there is no official subdivision. However, the Lunar geologic timescale embraces several major divisions relating to the Hadean, so these are sometimes used in an informal sense to refer to the same periods of time on Earth.
The initial crust, formed when the Earth's surface first solidified, totally disappeared from a combination of this fast Hadean plate tectonics and the intense impacts of the Late Heavy Bombardment. However, it is thought that it was basaltic in composition, like today's oceanic crust, because little crustal differentiation had yet taken place. The first larger pieces of continental crust, which is a product of differentiation of lighter elements during partial melting in the lower crust, appeared at the end of the Hadean, about 4.0 Ga. What is left of these first small continents are called cratons. These pieces of late Hadean and early Archean crust form the cores around which today's continents grew.
The Story begins with the wreckage of a cruise ship in the Pacific Ocean. A young Iburi Kyouka is stranded on a rock. A few years later, a research team is sent to the Pacific Ocean in search of The Book of the Dead. After Yuno finds out that the Book of the Dead is somewhere close by, the Hadeans begin their attack on the planet. Swarms of Beezlebugs form into batches and then large monsters (Hadeans) appear. Aiba Shu who was in custody gets released and is ordered to work with his team to eliminate the Hadeans. Yuno and Nanao find the Book of the Dead and is caught by Kyouka's private agents. Aiba's Viper becomes unusable due to the Beezlebugs and if forced to eject his armor. He gets beaten by a ground Hadean and dies when Yuno reaches him. Yuno becomes upset and stabs Aiba with the Book of the Dead.
The Eoarchean (; also spelled Eoarchaean) is the first era of the Archean Eon of the geologic record for which the Earth has a solid crust. It spans 400 million years from the end of the Hadean Eon 4 billion years ago (4000 Mya) to the start of the Paleoarchean Era 3600 Mya. The beginnings of life on Earth have been dated to this era and evidence of cyanobacteria date to 3500 Mya, just outside this era. At that time, the atmosphere was without oxygen and the pressure values ranged from 10 to 100 bar (around 10 to 100 atmospheres).
In 2010, an alternative scale was proposed that includes the addition of the Chaotian and Prenephelean Eons preceding the Hadean, and divides the Hadean into three eras with two periods each. The Paleohadean era consists of the Hephaestean (4.5–4.4 Ga) and the Jacobian periods (4.4–4.3 Ga). The Mesohadean is divided into the Canadian (4.3–4.2 Ga) and the Procrustean periods (4.2–4.1 Ga). The Neohadean is divided into the Acastan (4.1–4.0 Ga) and the Promethean periods (4.0–3.9 Ga).[6] As of February2017, this has not been adopted by the IUGS.
Alternatively it is defined as the first era of the Hadean eon, before the formation of the first crust on the Earth. As of 2012, it is considered to be part of a proposed revision of the Precambrian time scale.
The Cryptic era is an informal term for the earliest geologic evolution of the Earth and Moon. It is the oldest (informal) era of the Hadean eon, and it is commonly accepted to have begun close to 4533 million (about 4.533 billion) years ago when the Earth and Moon formed. No samples exist to date the transition between the Cryptic era and the following Basin Groups era for the Moon (see also Pre-Nectarian), though sometimes it is stated that this era ended 4150 million years ago for one or both of these bodies. Neither this time period, nor any other Hadean subdivision, has been officially recognized by the International Commission on Stratigraphy.
In the geologic record the Chaotian eon or era is unofficially proposed to denote the time preceding the solidification of the Earth's crust and the formation of Earth's moon, it is the earliest era within the eon of Hadean. It lasted 196 million years, at to the beginning of the Zirconian era, . It is named after Chaos, the primeval void in Greek mythology. The Chaotian sets in with the emergence of Earth at 4.6 billion years ago. Its upper limit and thus the transition to the Zirconian era is defined by the occurrence of the first conservation capable mineral. These are zircon, the oldest mineral in the Jack Hills of Narryer Gneiss Terrane in Western Australia (Yilgarn craton) found and were dated 4,404 ± 8 million years ago 
Eoarchean geology is important in investigating earth's tectonic history. It is because the earth had just undergone an transformation to the present-day-similar convective mode and lithosphere from a magma ocean in Hadean Eon, to either a protoplate tectonics or an unstable stagnant lithosphere lid at its infant stages. The earth's condition during Archean to Proterozoic (including Eoarchean era) serves as a crucial linkage between Hadean magma ocean to present-day plate tectonics. Various interpretations have been suggested to explain the prevalent tectonic style corresponding to Eoarchean geology. However it can be, in general, classified into two tectonic models, which are vertical tectonics and plate tectonics.
The Precambrian era dates from the beginning of Earth’s formation (4.6 billion years ago) to the beginning of the Cambrian era, 542 million years ago. The Precambrian consists of the Hadean, Archaean and Proterozoic Eons. Specifically, this article will examine the Ediacaran, when the first multicellular bodies are believed to have arisen, as well as what caused the rise of muticellularity. This time period arose after the Snowball Earth of the mid Neoproterozoic. The "Snowball Earth" was a period of worldwide glaciation, which is believed to have served as a population bottleneck for the subsequent evolution of multicellular organisms.
Hadean zircon has very low abundance around the globe because of recycling of material by plate tectonics. When the rock at the surface is buried deep in the Earth it is heated and can recrystallise or melt. In the Jack Hills, Australia, scientists obtained a relatively comprehensive record of Hadean zircon crystals in contrast to other locations. The Jack Hills rocks are from the Archean eon, about 3.6 billion years old. However, the zircon crystals there are older than the rocks that contain them. Many investigations have been carried out to find the absolute age and properties of zircon, for example the isotope ratios, mineral inclusions, and geochemistry of zircon. The characteristics of Hadean zircons show early Earth history and the mechanism of Earth's processes in the past. Based on the properties of these zircon crystals, many different geological models were proposed.
A September 2008 study of zircons found that Australian Hadean rock holds minerals pointing to the existence of plate tectonics as early as 4 billion years.[17][18] If this is true, the time when Earth finished its transition from having a hot, molten surface and atmosphere full of carbon dioxide, to being very much like it is today, can be roughly dated to about 4.0 billion years ago. The actions of plate tectonics and the oceans trapped vast amounts of carbon dioxide, thereby reducing the greenhouse effect and leading to a much cooler surface temperature and the formation of solid rock, and possibly even life.[17][18]
The Hadean, Archean and Proterozoic eons were as a whole formerly called the Precambrian. This covered the four billion years of Earth history prior to the appearance of hard-shelled animals. More recently, however, the Archean and Proterozoic eons have been subdivided into eras of their own.
Chaotian (geology)– Proposed era of, or eon preceding, the Hadean eon Formation and evolution of the Solar System– Formation of the Solar System by gravitational collapse of a molecular cloud and subsequent geological history Hadean zircon– The oldest-surviving crustal material from the Earth's earliest geological time period History of Earth– The development of planet Earth from its formation to the present day– the first sections describe the formation of the Earth Oldest dated rocks– Includes rocks over 4 billion years old from the Hadean Eon Precambrian– The earliest part of Earth's history Timeline of natural history
The Jack Hills zircon led to something of a revolution in our understanding of the Hadean eon. Older references generally show that Hadean Earth had a molten surface with prominent volcanos. The name "Hadean" itself refers to the "hellish" conditions assumed on Earth for the time, from the Greek Hades. Zircon dating suggested, albeit controversially, that the Hadean surface was solid, temperate, and covered by acidic oceans. This picture derives from the presence of particular isotopic ratios that suggest the action of water-based chemistry at some time before the formation of the oldest rocks (see Cool early Earth).
By adopting uranium-lead dating (U-Pb) together with other analytical methods, more geochemical information can be obtained. Only 3% out of over 200,000 detritial zircon grains dated by U-Pb analysis are over four billion years old.
Due to different content of uranium and trace element concentration, four clusters of zircons are identified as below 
Low crystallisation temperatures and trace element characteristics are the two major characteristics that differentiate mantle derived zircon or oceanic crust-derived zircon. Lunar and meteoritic zircons are unique because of their REE signature for example, lack of a cerium anomaly. The crystallization temperature ranges from 900 to 1100 °C. In contrast, terrestrial Hadean zircons are restricted to 600 to 780 °C. Hadean Jack Hills zircon has a wide range of oxygen fraction comparing to meteoritic zircons. No extraterrestrial zircons were found in any terrestrial locality. The textural characteristics like the growth zoning and inclusion mineralogy shows that Hadean zircon from the Jack Hills all come from igneous sources.
The International Commission on Stratigraphy now officially recognizes the Eoarchean Era as the
first part of the Archaean Eon, preceded by the Hadean Eon, during which the Earth is believed to have been essentially molten.
Since little or no geological evidence on Earth exists from the time spanned by the pre-Nectarian period of the Moon, the pre-Nectarian has been used as a guide by at least one notable scientific work to subdivide the unofficial terrestrial Hadean eon. In particular, it is sometimes found that the Hadean eon is subdivided into the Cryptic era, Basin Groups 1-9, Nectarian and Lower Imbrian, though the first two of these lunar divisions are informal and collectively make up the pre-Nectarian.
In A.D. 2031, humans are enjoying a prosperous existence until strange life forms called Hadeans appear. They suddenly begin to multiply and assault the human population. As a countermeasure, mankind organizes the N.I.D.F. (Neo International Defense Force) to investigate the Hadeans and protect themselves.
During Hadean time (4.6–4 Ga), the Solar System was forming, probably within a large cloud of gas and dust around the sun, called an accretion disc from which Earth formed .
The Hadean Eon is not formally recognized, but it essentially marks the era before we have adequate record of significant solid rocks. The oldest dated zircons date from about .