A cone is an organ on plants in the division Pinophyta that contains the reproductive structures. The familiar woody cone is the female cone; the male cones, which produce pollen, are herbaceous and much less conspicuous at full maturity. The name "cone" derives from the fact; the individual plates of a cone are known as scales. The male cone is structurally similar across all conifers, differing only in small ways from species to species. Extending out from a central axis are microsporophylls. Under each microsporophyll is several microsporangia; the female cone contains ovules. The female cone structure varies more markedly between the different conifer families, is crucial for the identification of many species of conifers; the members of the pine family have cones. These pine cones the woody female cones, are considered the "archetypal" tree cones; the female cone has two types of scale: the bract scales, the seed scales, one subtended by each bract scale, derived from a modified branchlet. On the upper-side base of each seed scale are two ovules that develop into seeds after fertilization by pollen grains.
The bract scales develop first, are conspicuous at the time of pollination. The scales open temporarily to receive gametophytes close during fertilization and maturation, re-open again at maturity to allow the seed to escape. Maturation takes 6–8 months from pollination in most Pinaceae genera, but 12 months in cedars and 18–24 months in most pines; the cones open either by the seed scales flexing back when they dry out, or by the cones disintegrating with the seed scales falling off. The cones are conic, cylindrical or ovoid, small to large, from 2–60 cm long and 1–20 cm broad. After ripening, the opening of non-serotinous pine cones is associated with their moisture content—cones are open when dry and closed when wet; this assures that the small, wind disseminated seeds will be dispersed during dry weather, thus, the distance traveled from the parent tree will be enhanced. A pine cone will go through many cycles of opening and closing during its life span after seed dispersal is complete; this process occurs with older cones while attached to branches and after the older cones have fallen to the forest floor.
The condition of fallen pine cones is a crude indication of the forest floor's moisture content, an important indication of wildfire risk. Closed cones indicate damp conditions; as a result of this, pine cones have been used by people in temperate climates to predict dry and wet weather hanging a harvested pine cone from some string outside to measure the humidity of the air. Members of the Araucariaceae have the bract and seed scales fused, have only one ovule on each scale; the cones are spherical or nearly so, large to large, 5–30 cm diameter, mature in 18 months. In Agathis, the seeds are winged and separate from the seed scale, but in the other two genera, the seed is wingless and fused to the scale; the cones of the Podocarpaceae are similar in function, though not in development, to those of the Taxaceae, being berry-like with the scales modified, evolved to attract birds into dispersing the seeds. In most of the genera, two to ten or more scales are fused together into a swollen, brightly coloured, edible fleshy aril.
Only one or two scales at the apex of the cone are fertile, each bearing a single wingless seed, but in Saxegothaea several scales may be fertile. The fleshy scale complex is 0.5–3 cm long, the seeds 4–10 mm long. In some genera, the scales are minute and not fleshy, but the seed coat develops a fleshy layer instead, the cone having the appearance of one to three small plums on a central stem; the seeds have a hard coat evolved to resist digestion in the bird's stomach. Members of the cypress family differ in that the bract and seed scales are fused, with the bract visible as no more than a small lump or spine on the scale; the botanical term galbulus is sometimes used instead of strobilus for members of this family. The female cones have one to 20 ovules on each scale, they have peltate scales, as opposed to the imbricate cones described above, though some have imbricate scales. The cones are small, 0.3–6 cm or 1⁄8–2 3⁄8 inches long, spherical or nearly so, like those of Nootka cypress, while others, such as western redcedar and California incense-cedar, are narrow.
The scales are arranged either spirally, or in decussate whorls of two or three four. The genera with spiral scale arrangement were treated in a separate family in the past. In most of the genera, the cones are woody and the seeds have two narrow wings, but in three genera, the seeds are wingless, in Juniperus, the cones are fleshy and
The Cretaceous is a geologic period and system that spans 79 million years from the end of the Jurassic Period 145 million years ago to the beginning of the Paleogene Period 66 mya. It is the last period of the Mesozoic Era, the longest period of the Phanerozoic Eon; the Cretaceous Period is abbreviated K, for its German translation Kreide. The Cretaceous was a period with a warm climate, resulting in high eustatic sea levels that created numerous shallow inland seas; these oceans and seas were populated with now-extinct marine reptiles and rudists, while dinosaurs continued to dominate on land. During this time, new groups of mammals and birds, as well as flowering plants, appeared; the Cretaceous ended with the Cretaceous–Paleogene extinction event, a large mass extinction in which many groups, including non-avian dinosaurs and large marine reptiles died out. The end of the Cretaceous is defined by the abrupt Cretaceous–Paleogene boundary, a geologic signature associated with the mass extinction which lies between the Mesozoic and Cenozoic eras.
The Cretaceous as a separate period was first defined by Belgian geologist Jean d'Omalius d'Halloy in 1822, using strata in the Paris Basin and named for the extensive beds of chalk, found in the upper Cretaceous of Western Europe. The name Cretaceous was derived from Latin creta; the Cretaceous is divided into Early and Late Cretaceous epochs, or Lower and Upper Cretaceous series. In older literature the Cretaceous is sometimes divided into three series: Neocomian and Senonian. A subdivision in eleven stages, all originating from European stratigraphy, is now used worldwide. In many parts of the world, alternative local subdivisions are still in use; as with other older geologic periods, the rock beds of the Cretaceous are well identified but the exact age of the system's base is uncertain by a few million years. No great extinction or burst of diversity separates the Cretaceous from the Jurassic. However, the top of the system is defined, being placed at an iridium-rich layer found worldwide, believed to be associated with the Chicxulub impact crater, with its boundaries circumscribing parts of the Yucatán Peninsula and into the Gulf of Mexico.
This layer has been dated at 66.043 Ma. A 140 Ma age for the Jurassic-Cretaceous boundary instead of the accepted 145 Ma was proposed in 2014 based on a stratigraphic study of Vaca Muerta Formation in Neuquén Basin, Argentina. Víctor Ramos, one of the authors of the study proposing the 140 Ma boundary age sees the study as a "first step" toward formally changing the age in the International Union of Geological Sciences. From youngest to oldest, the subdivisions of the Cretaceous period are: Late Cretaceous Maastrichtian – Campanian – Santonian – Coniacian – Turonian – Cenomanian – Early Cretaceous Albian – Aptian – Barremian – Hauterivian – Valanginian – Berriasian – The high sea level and warm climate of the Cretaceous meant large areas of the continents were covered by warm, shallow seas, providing habitat for many marine organisms; the Cretaceous was named for the extensive chalk deposits of this age in Europe, but in many parts of the world, the deposits from the Cretaceous are of marine limestone, a rock type, formed under warm, shallow marine circumstances.
Due to the high sea level, there was extensive space for such sedimentation. Because of the young age and great thickness of the system, Cretaceous rocks are evident in many areas worldwide. Chalk is a rock type characteristic for the Cretaceous, it consists of coccoliths, microscopically small calcite skeletons of coccolithophores, a type of algae that prospered in the Cretaceous seas. In northwestern Europe, chalk deposits from the Upper Cretaceous are characteristic for the Chalk Group, which forms the white cliffs of Dover on the south coast of England and similar cliffs on the French Normandian coast; the group is found in England, northern France, the low countries, northern Germany, Denmark and in the subsurface of the southern part of the North Sea. Chalk is not consolidated and the Chalk Group still consists of loose sediments in many places; the group has other limestones and arenites. Among the fossils it contains are sea urchins, belemnites and sea reptiles such as Mosasaurus. In southern Europe, the Cretaceous is a marine system consisting of competent limestone beds or incompetent marls.
Because the Alpine mountain chains did not yet exist in the Cretaceous, these deposits formed on the southern edge of the European continental shelf, at the margin of the Tethys Ocean. Stagnation of deep sea currents in middle Cretaceous times caused anoxic conditions in the sea water leaving the deposited organic matter undecomposed. Half the worlds petroleum reserves were laid down at this time in the anoxic conditions of what would become the Persian Gulf and the Gulf of Mexico. In many places around the world, dark anoxic shales were formed during this interval; these shales are an important source rock for oil and gas, for example in the subsurface of the North Sea. During th
The flowering plants known as angiosperms, Angiospermae or Magnoliophyta, are the most diverse group of land plants, with 64 orders, 416 families 13,164 known genera and c. 369,000 known species. Like gymnosperms, angiosperms are seed-producing plants. However, they are distinguished from gymnosperms by characteristics including flowers, endosperm within the seeds, the production of fruits that contain the seeds. Etymologically, angiosperm means a plant; the term comes from the Greek words sperma. The ancestors of flowering plants diverged from gymnosperms in the Triassic Period, 245 to 202 million years ago, the first flowering plants are known from 160 mya, they diversified extensively during the Early Cretaceous, became widespread by 120 mya, replaced conifers as the dominant trees from 100 to 60 mya. Angiosperms differ from other seed plants in several ways, described in the table below; these distinguishing characteristics taken together have made the angiosperms the most diverse and numerous land plants and the most commercially important group to humans.
Angiosperm stems are made up of seven layers. The amount and complexity of tissue-formation in flowering plants exceeds that of gymnosperms; the vascular bundles of the stem are arranged such that the phloem form concentric rings. In the dicotyledons, the bundles in the young stem are arranged in an open ring, separating a central pith from an outer cortex. In each bundle, separating the xylem and phloem, is a layer of meristem or active formative tissue known as cambium. By the formation of a layer of cambium between the bundles, a complete ring is formed, a regular periodical increase in thickness results from the development of xylem on the inside and phloem on the outside; the soft phloem becomes crushed, but the hard wood persists and forms the bulk of the stem and branches of the woody perennial. Owing to differences in the character of the elements produced at the beginning and end of the season, the wood is marked out in transverse section into concentric rings, one for each season of growth, called annual rings.
Among the monocotyledons, the bundles are more numerous in the young stem and are scattered through the ground tissue. They once formed the stem increases in diameter only in exceptional cases; the characteristic feature of angiosperms is the flower. Flowers show remarkable variation in form and elaboration, provide the most trustworthy external characteristics for establishing relationships among angiosperm species; the function of the flower is to ensure fertilization of the ovule and development of fruit containing seeds. The floral apparatus may arise terminally from the axil of a leaf; as in violets, a flower arises singly in the axil of an ordinary foliage-leaf. More the flower-bearing portion of the plant is distinguished from the foliage-bearing or vegetative portion, forms a more or less elaborate branch-system called an inflorescence. There are two kinds of reproductive cells produced by flowers. Microspores, which will divide to become pollen grains, are the "male" cells and are borne in the stamens.
The "female" cells called megaspores, which will divide to become the egg cell, are contained in the ovule and enclosed in the carpel. The flower may consist only of these parts, as in willow, where each flower comprises only a few stamens or two carpels. Other structures are present and serve to protect the sporophylls and to form an envelope attractive to pollinators; the individual members of these surrounding structures are known as petals. The outer series is green and leaf-like, functions to protect the rest of the flower the bud; the inner series is, in general, white or brightly colored, is more delicate in structure. It functions to attract bird pollinators. Attraction is effected by color and nectar, which may be secreted in some part of the flower; the characteristics that attract pollinators account for the popularity of flowers and flowering plants among humans. While the majority of flowers are perfect or hermaphrodite, flowering plants have developed numerous morphological and physiological mechanisms to reduce or prevent self-fertilization.
Heteromorphic flowers have short carpels and long stamens, or vice versa, so animal pollinators cannot transfer pollen to the pistil. Homomorphic flowers may employ a biochemical mechanism called self-incompatibility to discriminate between self and non-self pollen grains. In other species, the male and female parts are morphologically separated, developing on different flowers; the botanical term "Angiosperm", from the Ancient Greek αγγείον, angeíon and σπέρμα, was coined in the form Angiospermae by Paul Hermann in 1690, as the name of one of his primary divisions of the plant kingdom. This included flowering plants possessing seeds enclosed in capsules, distinguished from his Gymnospermae, or flowering plants with achenial or schizo-carpic fruits, the whole fruit or each of its pieces being here regarded as a seed and naked; the term and its antonym were maintained by Carl Linnaeus with the same sense, but with restricted application, in the names of the orders of his class Didynamia. Its use with any
In botany, a fruit is the seed-bearing structure in flowering plants formed from the ovary after flowering. Fruits are the means. Edible fruits, in particular, have propagated with the movements of humans and animals in a symbiotic relationship as a means for seed dispersal and nutrition. Accordingly, fruits account for a substantial fraction of the world's agricultural output, some have acquired extensive cultural and symbolic meanings. In common language usage, "fruit" means the fleshy seed-associated structures of a plant that are sweet or sour, edible in the raw state, such as apples, grapes, lemons and strawberries. On the other hand, in botanical usage, "fruit" includes many structures that are not called "fruits", such as bean pods, corn kernels and wheat grains; the section of a fungus that produces spores is called a fruiting body. Many common terms for seeds and fruit do not correspond to the botanical classifications. In culinary terminology, a fruit is any sweet-tasting plant part a botanical fruit.
However, in botany, a fruit is the ripened ovary or carpel that contains seeds, a nut is a type of fruit and not a seed, a seed is a ripened ovule. Examples of culinary "vegetables" and nuts that are botanically fruit include corn, eggplant, sweet pepper, tomato. In addition, some spices, such as allspice and chili pepper, are fruits. In contrast, rhubarb is referred to as a fruit, because it is used to make sweet desserts such as pies, though only the petiole of the rhubarb plant is edible, edible gymnosperm seeds are given fruit names, e.g. ginkgo nuts and pine nuts. Botanically, a cereal grain, such as corn, rice, or wheat, is a kind of fruit, termed a caryopsis. However, the fruit wall is thin and is fused to the seed coat, so all of the edible grain is a seed; the outer edible layer, is the pericarp, formed from the ovary and surrounding the seeds, although in some species other tissues contribute to or form the edible portion. The pericarp may be described in three layers from outer to inner, the epicarp and endocarp.
Fruit that bears a prominent pointed terminal projection is said to be beaked. A fruit results from maturation of one or more flowers, the gynoecium of the flower forms all or part of the fruit. Inside the ovary/ovaries are one or more ovules where the megagametophyte contains the egg cell. After double fertilization, these ovules will become seeds; the ovules are fertilized in a process that starts with pollination, which involves the movement of pollen from the stamens to the stigma of flowers. After pollination, a tube grows from the pollen through the stigma into the ovary to the ovule and two sperm are transferred from the pollen to the megagametophyte. Within the megagametophyte one of the two sperm unites with the egg, forming a zygote, the second sperm enters the central cell forming the endosperm mother cell, which completes the double fertilization process; the zygote will give rise to the embryo of the seed, the endosperm mother cell will give rise to endosperm, a nutritive tissue used by the embryo.
As the ovules develop into seeds, the ovary begins to ripen and the ovary wall, the pericarp, may become fleshy, or form a hard outer covering. In some multiseeded fruits, the extent to which the flesh develops is proportional to the number of fertilized ovules; the pericarp is differentiated into two or three distinct layers called the exocarp and endocarp. In some fruits simple fruits derived from an inferior ovary, other parts of the flower, fuse with the ovary and ripen with it. In other cases, the sepals, petals and/or stamens and style of the flower fall off; when such other floral parts are a significant part of the fruit, it is called an accessory fruit. Since other parts of the flower may contribute to the structure of the fruit, it is important to study flower structure to understand how a particular fruit forms. There are three general modes of fruit development: Apocarpous fruits develop from a single flower having one or more separate carpels, they are the simplest fruits. Syncarpous fruits develop from a single gynoecium having two or more carpels fused together.
Multiple fruits form from many different flowers. Plant scientists have grouped fruits into three main groups, simple fruits, aggregate fruits, composite or multiple fruits; the groupings are not evolutionarily relevant, since many diverse plant taxa may be in the same group, but reflect how the flower organs are arranged and how the fruits develop. Simple fruits can be either dry or fleshy, result from the ripening of a simple or compound ovary in a flower with only one pistil. Dry fruits may be either dehiscent, or indehiscent. Types of dry, simple fruits, examples of each, include: achene – most seen in aggregate fruits capsule – caryopsis – cypsela – an achene-like fruit derived from the individual florets in a capitulum. Fibrous drupe – follicle – is formed from a single carpel, opens by one suture
A transitional fossil is any fossilized remains of a life form that exhibits traits common to both an ancestral group and its derived descendant group. This is important where the descendant group is differentiated by gross anatomy and mode of living from the ancestral group; these fossils serve as a reminder that taxonomic divisions are human constructs that have been imposed in hindsight on a continuum of variation. Because of the incompleteness of the fossil record, there is no way to know how close a transitional fossil is to the point of divergence. Therefore, it cannot be assumed that transitional fossils are direct ancestors of more recent groups, though they are used as models for such ancestors. In 1859, when Charles Darwin's On the Origin of Species was first published, the fossil record was poorly known. Darwin described the perceived lack of transitional fossils as, "... the most obvious and gravest objection which can be urged against my theory," but explained it by relating it to the extreme imperfection of the geological record.
He noted the limited collections available at that time, but described the available information as showing patterns that followed from his theory of descent with modification through natural selection. Indeed, Archaeopteryx was discovered just two years in 1861, represents a classic transitional form between earlier, non-avian dinosaurs and birds. Many more transitional fossils have been discovered since and there is now abundant evidence of how all classes of vertebrates are related, including many transitional fossils. Specific examples of class-level transitions are: tetrapods and fish and dinosaurs, mammals and "mammal-like reptiles"; the term "missing link" has been used extensively in popular writings on human evolution to refer to a perceived gap in the hominid evolutionary record. It is most used to refer to any new transitional fossil finds. Scientists, however, do not use the term. In evolutionary taxonomy, the prevailing form of taxonomy during much of the 20th century and still used in non-specialist textbooks, taxa based on morphological similarity are drawn as "bubbles" or "spindles" branching off from each other, forming evolutionary trees.
Transitional forms are seen as falling between the various groups in terms of anatomy, having a mixture of characteristics from inside and outside the newly branched clade. With the establishment of cladistics in the 1990s, relationships came to be expressed in cladograms that illustrate the branching of the evolutionary lineages in stick-like figures; the different so-called "natural" or "monophyletic" groups form nested units, only these are given phylogenetic names. While in traditional classification tetrapods and fish are seen as two different groups, phylogenetically tetrapods are considered a branch of fish. Thus, with cladistics there is no longer a transition between established groups, the term "transitional fossils" is a misnomer. Differentiation occurs within groups, represented as branches in the cladogram. In a cladistic context, transitional organisms can be seen as representing early examples of a branch, where not all of the traits typical of the known descendants on that branch have yet evolved.
Such early representatives of a group are termed "basal taxa" or "sister taxa," depending on whether the fossil organism belongs to the daughter clade or not. A source of confusion is the notion that a transitional form between two different taxonomic groups must be a direct ancestor of one or both groups; the difficulty is exacerbated by the fact that one of the goals of evolutionary taxonomy is to identify taxa that were ancestors of other taxa. However, it is impossible to be sure that any form represented in the fossil record is a direct ancestor of any other. In fact, because evolution is a branching process that produces a complex bush pattern of related species rather than a linear process producing a ladder-like progression, because of the incompleteness of the fossil record, it is unlikely that any particular form represented in the fossil record is a direct ancestor of any other. Cladistics deemphasizes the concept of one taxonomic group being an ancestor of another, instead emphasizes the identification of sister taxa that share a more recent common ancestor with one another than they do with other groups.
There are a few exceptional cases, such as some marine plankton microfossils, where the fossil record is complete enough to suggest with confidence that certain fossils represent a population, ancestral to a population of a different species. But, in general, transitional fossils are considered to have features that illustrate the transitional anatomical features of actual common ancestors of different taxa, rather than to be actual ancestors. Archaeopteryx is a genus of theropod dinosaur related to the birds. Since the late 19th century, it has been accepted by palaeontologists, celebrated in lay reference works, as being the oldest known bird, though a study in 2011 has cast doubt on this assessment, suggesting instead that it is a non-avialan dinosaur related to the origin of birds, it lived in what is now southern Germany in the Late Jurassic period around 150 million years ago, when Europe was an archipelago in a shallow warm tropical sea, much closer to the equator than it is now. Similar in shape to a European magpie, with the largest individuals attaining the size of a raven, Archaeopteryx could grow to about 0.5 metres in length.
Despite its small size, broad wings, inferred ability to fly or glide, Archaeopteryx has more in common with other small Mesozoic dinosaurs than it does with modern birds. In particular, it sh
Welwitschia is a monotypic gymnosperm genus, comprising the distinctive Welwitschia mirabilis. The plant is known as welwitschia in English, but the name tree tumbo is used, it is called kharos or khurub in Nama, tweeblaarkanniedood in Afrikaans, nyanka in Damara, onyanga in Herero. Welwitschia is the only living genus of the family Welwitschiaceae and order Welwitschiales, in the division Gnetophyta. Informal sources refer to the plant as a "living fossil". Welwitschia mirabilis is endemic to the Namib desert within Angola. Welwitschia is named after the Austrian botanist and doctor Friedrich Welwitsch, the first European to describe the plant, in 1859 in present-day Angola. Welwitsch was so overwhelmed by the plant that he, "could do nothing but kneel down and gaze at it, half in fear lest a touch should prove it a figment of the imagination." Joseph Dalton Hooker of the Linnean Society of London, using Welwitsch's description and collected material along with material from the artist Thomas Baines who had independently recorded the plant in Namibia, described the species.
Welwitsch proposed calling the genus Tumboa after what he believed to be tumbo. Hooker asked Welwitsch for permission to name the genus Welwitschia instead. Welwitsch concurred and supplied some well-preserved material from which Hooker was able to make substantial progress in determining its botanical affinities; the taxonomy of Welwitschia subsequently changed intermittently with the development of new classification systems, its current taxonomic status is the same as Hooker's placement. Most botanists have treated Welwitschia as a distinct monotypic genus in a monotypic family or order. Most recent systems place Welwitschia mirabilis in its own family Welwitschiaceae in the gymnosperm order Gnetales. After germination, the seedling produces two cotyledons which grow to 25–35 mm in length, have reticulate venation. Subsequently, two foliage leaves are produced at the edge of a woody bilobed crown; the permanent leaves are opposite, parallel-veined and ribbon-shaped. Shortly after the appearance of the foliage leaves, the apical meristem dies and meristematic activity is transferred to the periphery of the crown.
The two foliage leaves grow continuously from a basal meristem reaching lengths up to 4 m. The tips of the leaves split and fray into several well-separated strap-shaped sections by the distortions of the woody portions surrounding the apical slit, by wind and adventitious external injuries; the largest specimens may be no more than 1.5 m tall above ground, but the circumference of the leaves in contact with the sand may exceed 8 m. Welwitschia has an elongated shallow root system consisting of "a tapering taproot with one or more non-tapering extensions, some pronounced lateral roots, a network of delicate spongy roots" and a woody fibrous unbranched main stem; the roots extend to a depth equal to the span of the living leaves from tip to tip. The main stem consists of an unbranched woody crown shaped like an inverted cone; the only branching in the shoot system occurs in the reproductive branches. The species is dioecious, with separate male and female plants. Fertilization is carried out by insects including true bugs.
The commonest of the true bugs attending Welwitschia is a member of the family Pyrrhocoridae, Probergrothius angolensis, but a hypothesized role in pollination has so far not been demonstrated. Infrequently and bees play a role as pollinators of Welwitschia. At least some of the pollinators are attracted by "nectar" produced on both male and female strobili. Welwitschia has been classified as a CAM plant after reconciliation of some contradictory and confusing data. There are however some puzzling aspects to the matter; the age of individual plants is difficult to assess. Some individuals may be more than 2000 years old; because Welwitschia only produces a single pair of foliage leaves, the plant was thought by some to be neotenic, consisting of a "giant seedling." However, research showed. Instead, the plant is more thought of as achieving its unusual morphology as a result of having "lost its head" at an early stage. Welwitschia mirabilis is endemic to the Kaokoveld Centre; the population is distributed southwards from the Bentiaba River in southern Angola, to the Kuiseb River in Namibia and up to 100 km inland of the coast.
The area is arid: the coast is recorded as having zero rainfall, while less than 100 mm of rain falls annually below the escarpment in the wet season from February to April. Populations tend to occur in ephemeral water courses, indicating a dependence on ground water in addition to precipitation from fog. Welwitschia mirabilis grows from seed, which may be bought from specialty seed dealers; the seeds have been shown to display orthodox seed behavior, which in general means that they may be stored for long periods at suitably low humidity and temperature. Welwitschia seeds develop suitably low water concentrations as they ripen. Removal of the outer seed coverings enhances germination performance, which suggests that the seeds may display non-deep physiological dormancy. On pl
Gondwana, was a supercontinent that existed from the Neoproterozoic until the Jurassic. It was formed by the accretion of several cratons. Gondwana became the largest piece of continental crust of the Paleozoic Era, covering an area of about 100,000,000 km2. During the Carboniferous Period, it merged with Laurussia to form a larger supercontinent called Pangaea. Gondwana broke up during the Mesozoic Era; the remnants of Gondwana make up about two thirds of today's continental area, including South America, Antarctica and the Indian Subcontinent. The formation of Gondwana began c. 800 to 650 Ma with the East African Orogeny, the collision of India and Madagascar with East Africa,and was completed c. 600 to 530 Ma with the overlapping Brasiliano and Kuunga orogenies, the collision of South America with Africa and the addition of Australia and Antarctica, respectively. The continent of Gondwana was named by Austrian scientist Eduard Suess, after the Gondwana region of central India, derived from Sanskrit for "forest of the Gonds".
The name had been used in a geological context, first by H. B. Medlicott in 1872, from which the Gondwana sedimentary sequences are described; the term "Gondwanaland" is preferred by some scientists in order to make a clear distinction between the region and the supercontinent. The assembly of Gondwana was a protracted process during the Neoproterozoic and Paleozoic, which however remains incompletely understood because of the lack of paleo-magnetic data. Several orogenies, collectively known as the Pan-African orogeny, led to the amalgamation of most of the continental fragments of a much older supercontinent, Rodinia. One of those orogenic belts, the Mozambique Belt, formed 800 to 650 Ma and was interpreted as the suture between East and West Gondwana. Three orogenies were recognized during the 1990s: the East African Orogeny and Kuunga orogeny, the collision between East Gondwana and East Africa in two steps, the Brasiliano orogeny, the successive collision between South American and African cratons.
The final stages of Gondwanan assembly overlapped with the opening of the Iapetus Ocean between Laurentia and western Gondwana. During this interval, the Cambrian explosion occurred. Laurentia was docked against the western shores of a united Gondwana for a short period near the Precambrian/Cambrian boundary, forming the short-lived and still disputed supercontinent Pannotia; the Mozambique Ocean separated the Congo–Tanzania–Bangweulu Block of central Africa from Neoproterozoic India. The Azania continent was an island in the Mozambique Ocean; the Australia/Mawson continent was still separated from India, eastern Africa, Kalahari by c. 600 Ma, when most of western Gondwana had been amalgamated. By c. 550 Ma, India had reached its Gondwanan position. Meanwhile, on the other side of the newly-forming Africa, Kalahari collided with Congo and Rio de la Plata which closed the Adamastor Ocean. C. 540–530 Ma, the closure of the Mozambique Ocean brought India next to Australia–East Antarctica, both North and South China were located in proximity to Australia.
As the rest of Gondwana formed, a complex series of orogenic events assembled the eastern parts of Gondwana c. 750 to 530 Ma. First the Arabian-Nubian Shield collided with eastern Africa in the East African Orogeny c.750 to 620 Ma. Australia and East Antarctica were merged with the remaining Gondwana c. 570 to 530 Ma in the Kuunga Orogeny. The Malagasy orogeny at about 550–515 Mya affected Madagascar, eastern East Africa and southern India. In it, Neoproterozoic India collided with the combined Azania and Congo–Tanzania–Bangweulu Block, suturing along the Mozambique Belt; the 18,000 km -long Terra Australis Orogen developed along Gondwana's western and eastern margins. Proto-Gondwanan Cambrian arc belts from this margin have been found in eastern Australia, New Zealand, Antarctica. Though these belts formed a continuous arc chain, the direction of subduction was different between the Australian-Tasmanian and New Zealand-Antarctica arc segments. A large number of terranes were accreted to Eurasia during Gondwana's existence but the Cambrian or Precambrian origin of many of these terranes remains uncertain.
For example, some Palaeozoic terranes and microcontinents that now make up Central Asia called the "Kazakh" and "Mongolian terranes", were progressively amalgamated into the continent Kazakhstania in the Late Silurian. Whether these blocks originated on the shores of Gondwana is not known. In the Early Palaeozoic the Armorican terrane, which today form large parts of France, was part of either Peri-Gondwana or core Gondwana. Precambrian rocks from the Iberian Peninsula suggest it too formed part of core Gondwana before its detachment as an orocline in the Variscan orogeny close to the Carboniferous–Permian boundary. South-east Asia is made of Gondwanan and Cathaysian continental fragments that were assembled during the Mid-Palaeozoic and Cenozoic; this p