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A snowball earthfrom around mya, is believed to have been caused by early photosynthetic organisms, which reduced the concentration of carbon dioxide and increased the amount of oxygen in the atmosphere. Charcoalification is an important taphonomic mode. Wildfire or burial in hot volcanic ash drives off the volatile compounds, leaving only a residue of pure carbon.
This is not a viable food source for fungi, herbivores or detritovores, so is prone to preservation. It is also robust, so can withstand pressure and display exquisite, sometimes sub-cellular, detail.
Evolution of life cycles[ edit ] Angiosperm life cycle All multicellular plants have a life cycle comprising two generations or phases. The pattern in plant evolution has been a shift from homomorphy to heteromorphy. The algal ancestors of land plants were almost certainly haplobionticbeing haploid for all their life cycles, with a unicellular zygote providing the 2N stage.
All land plants i. It has been proposed that the basis for the emergence of the diploid phase of the life cycle as the dominant phase, is that diploidy allows masking of the expression of deleterious mutations through genetic complementation. As the diploid phase was becoming predominant, the masking effect likely allowed genome sizeand hence information content, to increase without the constraint of having to improve accuracy of replication.
The opportunity to increase information content at low cost is advantageous because it permits new adaptations to be encoded. This view has been challenged, with evidence showing that selection is no more effective in the haploid than in the diploid phases of the lifecycle of mosses and angiosperms. The interpolation theory also known as the antithetic or intercalary theory  holds that the interpolation of a multicellular sporophyte phase between two successive gametophyte generations was an innovation caused by preceding meiosis in a freshly germinated zygote with one or more rounds of mitotic division, thereby producing some diploid multicellular tissue before finally meiosis produced spores.
This theory implies that the first sporophytes bore a very different and simpler morphology to the gametophyte they depended on. Increasing complexity of the ancestrally simple sporophyte, including the eventual acquisition of photosynthetic cells, would free it from its dependence on a gametophyte, as seen in some hornworts Anthocerosand eventually result in the sporophyte developing organs and vascular tissue, and becoming the dominant phase, as in the tracheophytes vascular plants.
The observed appearance of larger axial sizes, with room for photosynthetic tissue and thus self-sustainability, provides a possible route for the development of a self-sufficient sporophyte phase. Since the same genetic material would be employed by both the haploid and diploid phases they would look the same. This explains the behaviour of some algae, such as Ulva lactuca, which produce alternating phases of identical sporophytes and gametophytes.
Subsequent adaption to the desiccating land environment, which makes sexual reproduction difficult, might have resulted in the simplification of the sexually active gametophyte, and elaboration of the sporophyte phase to better disperse the waterproof spores. The earliest land plants did not have vascular systems for transport of water and nutrients either.
Aglaophytona rootless vascular plant known from Devonian fossils in the Rhynie chert  was the first land plant discovered to have had a mycorrhizal relationship with fungi  which formed arbusculesliterally "tree-like fungal roots", in a well-defined cylinder of cells ring in cross section in the cortex of its stems. The fungi fed on the plant's sugars, in exchange for nutrients generated or extracted from the soil especially phosphateto which the plant would otherwise have had no access.
Like other rootless land plants of the Silurian and early Devonian Aglaophyton may have relied on arbuscular mycorrhizal fungi for acquisition of water and nutrients from the soil. Xylem To photosynthesise, plants must absorb CO2 from the atmosphere. However, this comes at a price, since making the tissues available for CO2 to enter allows water to evaporate.
Early land plants transported water apoplasticallywithin the porous walls of their cells. Later, they evolved the ability to control water loss and CO2 acquisition through the use of a waterproof outer covering or cuticle perforated by stomatavariable apertures that could open and close to regulate evapotranspiration. Specialised water transport vascular tissues subsequently evolved, first in the form of hydroidsthen tracheids and secondary xylemfollowed by vessels in flowering plants.
This transition from poikilohydry to homoiohydry opened up new potential for colonisation. As CO2 was withdrawn from the atmosphere by plants, more water was lost in its capture, and more elegant water acquisition and transport mechanisms evolved.
By the end of the Carboniferous, when CO2 concentrations had been reduced to something approaching today's, around 17 times more water was lost per unit of CO2 uptake.
Even today, water transport takes advantage of the cohesion-tension property of water. Water can be wicked along a fabric with small spaces, and in narrow columns of water, such as those within the plant cell walls or in tracheids, when molecules evaporate from one end, they pull the molecules behind them along the channels. Therefore, transpiration alone provides the driving force for water transport in plants.
The bands are difficult to see on this specimen, as an opaque carbonaceous coating conceals much of the tube.
Bands are just visible in places on the left half of the image. During the early Silurian, they developed specialized xylem cells, with walls that were strengthened by bands of lignification or similar chemical compounds. The early Devonian pretracheophytes Aglaophyton and Horneophyton have unreinforced water transport tubes with wall structures very similar to the hydroids of modern moss sporophytes, but they grew alongside several species of tracheophytes, such as Rhynia gwynne-vaughanii that had well-reinforced xylem tracheids.
The earliest macrofossils known to have xylem tracheids are small, mid-Silurian plants of the genus Cooksonia. Thickened bands on the walls of tubes, apparent from the early Silurian onwards,  are adaptations to increase the resistance to collapse under tension   and, when they form single celled conduits, are referred to as tracheids.
These, the "next generation" of transport cell design, have a more rigid structure than hydroids, preventing their collapse at higher levels of water tension. This is an important role where water supply is not constant, and indeed stomata appear to have evolved before tracheids, since they are present in the sporophytes of mosses and the non-vascular hornworts. The endodermis can also provide an upwards pressure, forcing water out of the roots when transpiration is not enough of a driver.
Once plants had evolved this level of controlled water transport, they were truly homoiohydricable to extract water from their environment through root-like organs rather than relying on a film of surface moisture, enabling them to grow to much greater size. Pits in tracheid walls have very small diameters, preventing air bubbles from passing through to adjacent tracheids.
By the Carboniferous, Gymnosperms had developed bordered pits  valve-like structures that seal the pits when one side of a tracheid is depressurized. Defunct tracheids were retained to form a strong, woody stem, produced in most instances by a secondary xylem.
However, in early plants, tracheids were too mechanically vulnerable, and retained a central position, with a layer of tough sclerenchyma on the outer rim of the stems. Tracheids end with walls, which impose a great deal of resistance on flow;  vessel members have perforated end walls, and are arranged in series to operate as if they were one continuous vessel.
An embolism is where an air bubble is created in a tracheid. This may happen as a result of freezing, or by gases dissolving out of solution. Once an embolism is formed, it usually cannot be removed but see later ; the affected cell cannot pull water up, and is rendered useless.
End walls excluded, the tracheids of prevascular plants were able to operate under the same hydraulic conductivity as those of the first vascular plant, Cooksonia. The branching pattern of megaphyll veins may indicate their origin as webbed, dichotomising branches.
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The megaphyllous leaf architecture arose multiple times in different plant lineages Leaves are the primary photosynthetic organs of a modern plant. The origin of leaves was almost certainly triggered by falling concentrations of atmospheric CO2 during the Devonian period, increasing the efficiency with which carbon dioxide could be captured for photosynthesis. Based on their structure, they are classified into two types: It has been proposed that these structures arose independently.
All three steps happened multiple times in the evolution of today's leaves. However, Wolfgang Hagemann questioned it for morphological and ecological reasons and proposed an alternative theory. Axes such as stems and roots evolved later as new organs.
Rolf Sattler proposed an overarching process-oriented view that leaves some limited room for both the telome theory and Hagemann's alternative and in addition takes into consideration the whole continuum between dorsiventral flat and radial cylindrical structures that can be found in fossil and living land plants.
Thus, James  concluded that "it is now widely accepted that In fact, it is simply the timing of the KNOX gene expression! Today's megaphyll leaves probably became commonplace some mya, about 40my after the simple leafless plants had colonized the land in the Early Devonian. This spread has been linked to the fall in the atmospheric carbon dioxide concentrations in the Late Paleozoic era associated with a rise in density of stomata on leaf surface.
Increasing the stomatal density allowed for a better-cooled leaf, thus making its spread feasible, but increased CO2 uptake at the expense of decreased water use efficiency. The early to middle Devonian trimerophytes may be considered leafy. It is important to mention archaeological survey as well as excavation. Developed to provide diachronic information about a region rather than one specific site, contemporary landscape and vegetation has become an integral part of these studies e.
It is not expected that landscapes will have remained the same since human activity began, but understanding the diversity of species and ecological niches contributes towards a more holistic study of the region. It is also possible to carry out Geographical Information Systems analyses incorporating vegetation and landscape features into modelling past routes, for example.
Types of palaeobotanical remains Palaeobotanical material can be divided into macrofossils, visible to the naked eye, and microfossils that require magnification to examine. The identification of any botanical remains is dependent on analogies with modern flora and with archaeological reference collections Dincauze, Flowers and vegetative remains are rarely preserved in the archaeological record, except in special environmental conditions Box 1.
Macrofossils This category includes charcoal, carbonised or charred seeds, shells, and grains, root casts, impressions on clay, mineralized and petrified remains, and coprolites mineralized or dessicated faeces. In the Mediterranean, carbonization is the most common way that ancient botanical material has been preserved and ranges from large pieces of charcoal indicating structural destruction or firewood to charred seeds. These charred seeds tend to come from plants that require processing prior to consumption e.
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It is important to consider that plants eaten away from the settlement are unlikely to occur in archaeological assemblages, hence any picture of ancient diet based on macrofossils alone may be incomplete. The practice of taking casts where plant roots once pierced the soil has reached its fullest potential at the site of Pompeii, buried by the eruption of Vesuvius in ad Pioneered by Wilhelmina Jashemski, it is possible to identify not only the plant species that once grew here but to piece together the planting pattern and even irrigation systems of ancient gardens Jashemski, Casts can also be made of plant impressions, usually found on ceramics or other baked clay artefacts Magid and Krzywinski, For example, vine leaves are recognizable on the base of a ceramic basin from Myrtos Fournou Korifi in southern Crete Warren,hinting at the exploitation of the grape by humans early in the Bronze Age c.
Impressions like these on the bases of vessels are usually the result of the ceramics standing on mats to dry before firing, but others result from plant material that may have been deliberately incorporated as a temper for the clay or used in cords that were wound around the vessel. Mineralized plant remains are rare, requiring a special set of conditions for their creation, whereby dissolved minerals replace the plant cellular structure or encase the remains, such as caves or rock shelters Hansen, and cesspits Wilkinson and Stevens, Roman latrines are an excellent source of mineralized plant remains; at Sagalassos in Turkey, complex depositional processes have led to a combination of charred plant material with mineralized seeds in fifth—seventh-century ad latrine deposits, including fig Ficus caricaplum Prunus sp.
In contrast to other types of botanical remains, plant matter from coprolites is a reasonably secure indicator of plants that were consumed and defecated by humans, especially if the remains come from latrines, mummy intestines, or burials Reinhard and Bryant, Specific biomarkers also allow a distinction between human and animal faecal matter to be made, crucial when it comes to drawing conclusions about ancient human diet Shillito et al.
Coprolites are better preserved in arid regions and thus are more common finds in New World archaeology; indeed coprolite analysis has shown that edible flowers e. Yucca, Agave, Opuntia, Cucurbita spp. Microfossils and biomolecular analysis Microfossils such as phytoliths and pollen need magnification to be visible and such studies are complemented by an increasing number of biomolecular studies.
Phytoliths, or the silica skeletons from plant tissue, survive after a plant has died and their analysis can provide valuable information about use of space within a structure or site. For example, a study of the phytoliths from surfaces in the Neolithic village of Makri in northern Greece indicates the settlement was inhabited all year long and engaged in cereal farming and pastoralism, as well as helping identify areas for crop processing Tsartsidou et al.
Phytoliths can also be recovered from artefacts, showing, for example, whether a quern was used primarily for cereals or tubers Wilkinson and Stevens, As pollen grains are produced in varying amounts, shapes, and sizes by the male reproductive organs of all spermatophyte plants, palynology can be a useful tool in reconstructing the vegetation cover of landscapes in the past.
Only those which are anemophilous are recoverable through archaeological methods taking sediment cores from marshes or lacustrine areas where pollen is preserved in the waterlogged, anaerobic environmentleading to a preponderance of forest and grassy plants in any sample.
These requirements naturally limit the number of samples available in drier eastern Mediterranean countries such as Greece and Egypt.
Evolutionary history of plants - Wikipedia
It is also possible to recover pollen from coprolites, complementing the information on general vegetation cover with details about animal grazing or fodder practices, as well as human diet — even including whether plant matter was cooked Hunt et al.
This highlights one of the main advantages of phytolith studies compared to palynology for archaeologists, as the phytoliths tend to be deposited in the soil where the plant decays, thus giving a more immediate location for its growth or use.Plenty of fish ( POF) review , experience, rating
Moreover, pollen is often only identifiable to genus level e. Quercusso may not provide adequate specificity for any meaningful interpretation.
For this reason, palynology is generally used by archaeologists to look at vegetation on a regional level rather than providing site-specific information. Palynological investigation of the cores from Lake Kournas on Crete has revealed changes in the Holocene environment such as the arrival of the carob Ceratonia siliqua that can be linked to human activity, as well as to the Late Bronze Age eruption of the volcano on Santorini Bottema and Sarpaki, Vegetation burning and grazing can also be identified in the pollen record, furthering the understanding of prehistoric land management practices Atherden,