In Europe the biocidal products are divided into different product types (PT), based on their intended use. These product types, 22 in total under the BPR, are grouped into four main groups, namely disinfectants, preservatives, pest control, and other biocidal products. For example, the main group "disinfectants" contains products to be used for human hygiene (PT 1) and veterinary hygiene (PT 3), main group "preservatives" contains wood preservatives (PT 8), the main group "for pest control" contains rodenticides (PT 14) and repellents and attractants (PT 19), while the main group "other biocidal products" contains antifouling products (PT 21). It should noted that one active substance can be used in several product types, such as for example sulfuryl fluoride, which is approved for use as a wood preservative (PT 8) as well as an insecticide (PT 18).


Biocides can be added to other materials (typically liquids) to protect them against biological infestation and growth. For example, certain types of quaternary ammonium compounds (quats) are added to pool water or industrial water systems to act as an algicide, protecting the water from infestation and growth of algae. It is often impractical to store and use poisonous chlorine gas for water treatment, so alternative methods of adding chlorine are used. These include hypochlorite solutions, which gradually release chlorine into the water, and compounds like sodium dichloro-s-triazinetrione (dihydrate or anhydrous), sometimes referred to as "dichlor", and trichloro-s-triazinetrione, sometimes referred to as "trichlor". These compounds are stable while solids and may be used in powdered, granular, or tablet form. When added in small amounts to pool water or industrial water systems, the chlorine atoms hydrolyze from the rest of the molecule forming hypochlorous acid (HOCl) which acts as a general biocide killing germs, micro-organisms, algae, and so on. Halogenated hydantoin compounds are also used as biocides.


At temperatures above 228 °C (442 °F), the structure is isometric with a unit cell that is about 5.50 Å on an edge. This structure is based on cubic close-packed sulfur atoms, with copper and iron atoms randomly distributed into six of the eight tetrahedral sites located in the octants of the cube. With cooling, the Fe and Cu become ordered, so that 5.5 Å subcells in which all eight tetrahedral sites are filled alternate with subcells in which only four of the tetrahedral sites are filled; symmetry is reduced to orthorhombic.[4]


13. It is the antimony endmember of the continuous solid solution series with arsenic-bearing tennantite. Pure endmembers of the series are seldom if ever seen in nature. Of the two, the antimony rich phase is more common. Other elements also substitute in the structure, most notably iron and zinc, along with less common silver, mercury and lead. Bismuth also substitutes for the antimony site and bismuthian tetrahedrite or annivite is a recognized variety. The related, silver dominant, mineral species freibergite, although rare, is notable in that it can contain up to 18% silver.


Tetrahedrite gets its name from the distinctive tetrahedron shaped cubic crystals. The mineral usually occurs in massive form, it is a steel gray to black metallic mineral with Mohs hardness of 3.5 to 4 and specific gravity of 4.6 to 5.2.



PS II and PS I are connected by a transmembrane proton pump, cytochrome b

6 complex (plastoquinol—plastocyanin reductase; EC Electrons from PS II are carried by plastoquinol to cytb

6, where they are removed in a stepwise fashion (reforming plastoquinone) and transferred to a water-soluble electron carrier called plastocyanin. This redox process is coupled to the pumping of four protons across the membrane. The resulting proton gradient (together with the proton gradient produced by the water-splitting complex in PS II) is used to make ATP via ATP synthase.


Tetractys and Chemistry

In 1869 the Russian chemist Dmitri Mendeleev invented the periodic table of the elements, and classified all known atoms according to their atomic weight and chemical properties. Then in 1914 it was discovered that the key index of these elements was their atomic number. This is the number of protons (positively charged) found in the nucleus of an electrically neutral atom, and is equal to the number of electrons which carry a negative charge.

Interestingly, if we consider the atomic electron configuration table, and look at the increase of protons and electrons from one element to the next, we find the following sequence of values: 2, 8, 8, 18, 18, 32. These numbers can be expressed as 2x12, 2x22, 2x22, 2x32, 2x32, 2x42, being squares of the numbers of the Tetractys.

Without entering into a numerical analysis of the entire periodic table of chemical elements,

and leptons over anti-quarks


Science and the Hermetic Tradition have found an element of commonality many centuries after Pythagoras.

The Rosicrucian Beacon -- December 2008

in Group I (the alkali metals), Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Caesium (Cs), and Francium (Fr), are the chemical elements with atomic numbers equal to 3, 11, 19, 37, 55, 87. Taking into account the sequences mentioned above and the fact that Lithium (Li) possesses one proton more then helium (he), (with the atomic number 2), gives us the formula (1)+2, 8, 8, 18, 18, 32. This can be reduced to the square numbers of Tetractys as follows: 1+2x12, 2x22, 2x22, 2x32, 2x42. This shows that atoms, of which matter is composed, obey the specific law of numbers that the Pythagoreans had encoded in the Tetractys.


The Water Molecule

Another model in nature corresponding to the Tetractys is apparent in the threefold structure of a water molecule. A water molecule has a non- linear shape because it has two pairs of bonded electrons and two unshared pairs. When water solidifies, it becomes macroreticular and consists of molecules joined by hydrogen bonds. Each molecule then binds to four other water molecules geometrically in a pyramid when it turns to ice, where all the water molecules are linked by

Dmitri Mendeleev (1834-1907)

hydrogen bonds.

Raising the temperature results in the

intermolecular bonds changing from four to three, then to two with the transformation of ice into liquid water. Raising the temperature further, decreases the intermolecular links steadily, until at 100°C there is no longer any intermolecular connection and the water molecules become detached from each other in the process of evaporation. This is another example of the numbers of the Tetractys

replicated in Nature; the numbers 4, 3, 2 and 1 express the sequence of links in the process of the formation of ice. In nature, the tetrahedron is an example of great stability, which can be found even in the geometric form of a diamond crystal which in the Mohs scale of mineral hardness is at the very top of the scale.


Tetractys and Biology

In the microcosm, the Tetractys is well represented at the biological level of the molecules of amino acids, the basic building blocks of proteins, whose structural formula shows that Carbon (C), the building block of life, has four chains, Nitrogen (N) has three, Oxygen (O) has two and hydrogen (h) has one, the sum of which is ten, corresponding to the numbers of the Tetractys.

Even in the DNA molecule, it is possible to find traces of the numbers of the Tetractys: a chromosome contains a double strand of DNA, each strand being made up of 3 molecules (a base of nitrogen, a molecule of phosphate and a molecule of deoxyribose), the first of which (nitrogenous base) consists of 4 chemical varieties: Adenine, Thymine, Cytosine and Guanine (A, T, C, G). Each nucleotide binds to its complementary nucleotide with 2 or 3 hydrogen bonds and the double helix encloses 10 pairs of nucleotides.

In nature we find that the sperm or male reproductive cells, contain the male y chromosome or the female X chromosome, thereby demonstrating the dual polarity of our species. Each cell has two chromosomes, either Xy for a male or XX for a female. When the sperm (X or y chromosome) combines with the female

The Rosicrucian Beacon -- December 2008

Atoms, of which matter is composed, obey the specific law of numbers that the Pythagoreans had encoded in the Tetractys.


egg, which always has the X chromosome, a new life form begins. This is a clear demonstration of the Tetractys whose numbers act even on the most important biochemical structures of the human body.

Remaining in biology, but on a higher level, let us take a look at the cardiac system where the sacred numbers of the Pythagorean Tetractys are related to the morphology of the

heart that, as a unit, represents the number 1: it has 2 veins and 3 arteries (brachiocephalic or innominate artery, left common carotid artery and left subclavian, that arise from the arch of the aorta) and finally the 4 pulmonary veins, as well as 4 atria/ventricles. Among further examples of the Tetractys in nature, may be the pyramidal neurons of the cerebral cortex and the Purkinje cell in the cerebellar cortex. These cells that preside over the coordination and harmonisation of movement, seem to offer a clear sign of the relevance of the teachings of Pythagoras.


A greenhouse gas (often abbreviated as GHG) is a gas that both absorbs and emits radiation in the infrared range, commonly called thermal radiation or heat. When present in the atmosphere, these gases trap radiation in the form of heat, causing a warming process called the greenhouse effect. The presence of four major greenhouse gases, namely water vapor (H2O), carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) in the Earth's atmosphere keeps the average temperature of 15º C (59º F), whereas without the greenhouse effect the average temperature would be a frosty -18º C (0º F).


In population genetics, the four-gamete test is a method for detecting historical recombination events.[1]



Given a set of four or more sampled haploid chromosomes, the four-gamete test (FGT) detects recombination events by locating pairs of segregating sites that cannot have arisen without either recombination or a repeat mutation. Under the infinite-sites assumption (i.e. repeat mutations have zero probability), the probability of a repeat mutation is zero, and hence a recombination event is inferred. For example, if the data being studied consists of bi-allelic single-nucleotide polymorphism data, then the following configuration could be generated without recombination.


The F1 offspring of Mendel's pea crosses always looked like one of the two parental varieties. In this situation of "complete dominance," the dominant allele had the same phenotypic effect whether present in one or two copies. But for some characteristics, the F1 hybrids have an appearance in between the phenotypes of the two parental varieties. A cross between two four o'clock (Mirabilis jalapa) plants shows this common exception to Mendel's principles. Some alleles are neither dominant nor recessive. The F1 generation produced by a cross between red-flowered (RR) and white flowered (WW) Mirabilis jalapa plants consists of pink-colored flowers (RW). Which allele is dominant in this case? Neither one. This third phenotype results from flowers of the heterzygote having less red pigment than the red homozygotes. Cases in which one allele is not completely dominant over another are called incomplete dominance. In incomplete dominance, the heterozygous phenotype lies somewhere between the two homozygous phenotypes.


A similar situation arises from codominance, in which the phenotypes produced by both alleles are clearly expressed. For example, in certain varieties of chicken, the allele for black feathers is codominant with the allele for white feathers. Heterozygous chickens have a color described as "erminette", speckled with black and white feathers. Unlike the blending of red and white colors in heterozygous four o'clocks, black and white colors appear separately in chickens. Many human genes, including one for a protein that controls cholesterol levels in the blood, show codominance, too. People with the heterozygous form of this gene produce two different forms of the protein, each with a different effect on cholesterol levels.


In Mendelian inheritance, genes have only two alleles, such as a and A. In nature, such genes exist in several different forms and are therefore said to have multiple alleles. A gene with more than two alleles is said to have multiple alleles. An individual, of course, usually has only two copies of each gene, but many different alleles are often found within a population. One of the best-known examples is coat color in rabbits. A rabbit's coat color is determined by a single gene that has at least four different alleles. The four known alleles display a pattern of simple dominance that can produce four coat colors. Many other genes have multiple alleles, including the human genes for ABO blood type.


Furthermore, many traits are produced by the interaction of several genes. Traits controlled by two or more genes are said to be polygenic traits. Polygenic means "many genes." For example, at least three genes are involved in making the reddish-brown pigment in the eyes of fruit flies. Polygenic traits often show a wide range of phenotypes. The broad variety of skin color in humans comes about partly because at least four different genes probably control this trait.


In molecular cloning, a vector is a DNA molecule used as a vehicle to artificially carry foreign genetic material into another cell, where it can be replicated and/or expressed (e.g.- plasmid, cosmic, Lambda phages). A vector containing foreign DNA is termed recombinant DNA. The four major types of vectors are plasmids, viral vectors, cosmids, and artificial chromosomes. Of these, the most commonly used vectors are plasmids. Common to all engineered vectors are an origin of replication, a multicloning site, and a selectable marker.

Fiers' group expanded on their MS2 coat protein work, determining the complete nucleotide-sequence of bacteriophage MS2-RNA (whose genome encodes just four genes in 3569 base pairs [bp]) and Simian virus 40 in 1976 and 1978, respectively.[15][16]


To determine the sequence, four types of reversible terminator bases (RT-bases) are added and non-incorporated nucleotides are washed away


Population genetics is the branch of evolutionary biology responsible for investigating processes that cause changes in allele and genotype frequencies in populations based upon Mendelian inheritance.[3] Four different forces can influence the frequencies: natural selection, mutation, gene flow (migration), and genetic drift. A population can be defined as a group of interbreeding individuals and their offspring. For human genetics the populations will consist only of the human species. The Hardy-Weinberg principle is a widely used principle to determine allelic and genotype frequencies.


If you would like our suggestions and recommendations for Clearing your Acne please order the Try Me Pack of your choice, fill out our Profile and send it to us. Filling out a profile will insure that you’ve ordered the correct products for your particular skin conditions, as well as enable us to start you on the path to flawless skin much more quickly! Acne will always be a four-letter word unless you make an educated and informed decision to clear it up.



The Four Grades of Acne










Grade I


Consists predominantly of whiteheads (closed comedones) and blackheads (open comedones). There is an occasional inflammatory lesion, however there are at least 25 lesions on one side of the face at any given time.


Grade II


Maturation Arrest Acne is the most difficult to treat and evaluate. The face becomes STUDDED with many whiteheads (closed comedones) and from a distance looks clear. Up close the skin feels and looks rough. The lesion count reveals 50-100 whiteheads on only one side of the face with an occasional inflammatory lesion.


Grade III


In addition to mixture of whiteheads (closed comedones) and blackheads (open comedones) there are a constant number of inflammatory lesions (7-10,) pustules, and papules at any one time on one side of the face. Grade Three Acne is painful because of the swelling, size, and duration of the lesions.


Grade IV


Cystic acne contains all of the above lesions plus nodules and cysts. It is very painful both physically and emotionally with severe inflammation that is very red or purplish in color and is commonly called "Pizza Face" Acne. Grade Four responds very quickly to treatment because all of the lesions are on the surface.


There are four stages in coal formation: peat, lignite, bituminous and anthracite. The stage depends upon the conditions to which the plant remains are subjected after they were buried – the greater the pressure and heat, the higher the rank of coal. Higher-ranking coal is denser and contains less moisture and gases and has a higher heat value than lower-ranking coal.

Peat – Stage One
Peat is the first stage in the formation of coal. Normally, vegetable matter is oxidized to water and carbon dioxide. However, if plant material accumulates underwater, oxygen is not present and so only partial decomposition occurs. This incomplete destruction leads to the accumulation of an organic substance called peat.

Peat is a fibrous, soft, spongy substance in which plant remains are easily recognizable. It contains a large amount of water and must be dried before use. Therefore, it is seldom used as a source of heat. Peat burns with a long flame and considerable smoke.

Lignite – Stage Two
Lignite, the second stage, is formed when peat is subjected to increased vertical pressure from accumulating sediments. Lignite is dark brown in colour and, like peat, contains traces of plants. It is found in many places but is used only when more efficient fuel is not available. It crumbles easily and should not be shipped or handled before use.

Bituminous Coal – Stage Three
Bituminous Coal is the third stage. Added pressure has made it compact and virtually all traces of plant life have disappeared. Also known as “soft coal”, bituminous coal is the type found in Cape Breton and is our most abundant fuel. It is greatly used in industry as a source of heat energy.

Anthracite – Stage Four
Anthracite, the fourth stage in coal formation, is also known as “hard coal” because it is hard and has a high lustre. It appears to have been formed as a result of combined pressure and high temperature. Anthracite burns with a short flame and little smoke.

Nuclear weapons tests have historically been divided into four categories reflecting the medium or location of the test.

Atmospheric testing designates explosions that take place in the atmosphere. Generally these have occurred as devices detonated on towers, balloons, barges, islands, or dropped from airplanes, and also those only buried far enough to intentionally create a surface-breaking crater. Nuclear explosions close enough to the ground to draw dirt and debris into their mushroom cloud can generate large amounts of nuclear fallout due to irradiation of the debris. This definition of atmospheric is used in the Limited Test Ban Treaty, which banned this class of testing along with exoatmospheric and underwater.

Underground testing refers to nuclear tests conducted under the surface of the earth, at varying depths. Underground nuclear testing made up the majority of nuclear tests by the United States and the Soviet Union during the Cold War; other forms of nuclear testing were banned by the Limited Test Ban Treaty in 1963. True underground tests are intended to be fully contained and emit a negligible amount of fallout. Unfortunately these nuclear tests do occasionally "vent" to the surface, producing from nearly none to considerable amounts of radioactive debris as a consequence. Underground testing, almost by definition, causes seismic activity of a magnitude that depends on the yield of the nuclear device and the composition of the medium it is detonated in, and generally creates a subsidence crater.[2] In 1976, the United States and the USSR agreed to limit the maximum yield of underground tests to 150 kt with the Threshold Test Ban Treaty.

Underground testing also falls into two physical categories: tunnel tests in generally horizontal tunnel drifts, and shaft tests in vertically drilled holes.

Exoatmospheric testing refers to nuclear tests conducted above the atmosphere. The test devices are lifted on rockets. These high altitude nuclear explosions can generate a nuclear electromagnetic pulse (NEMP) when they occur in the ionosphere, and charged particles resulting from the blast can cross hemispheres following geomagnetic lines of force to create an auroral display.

Underwater testing results from nuclear devices being detonated underwater, usually moored to a ship or a barge (which is subsequently destroyed by the explosion). Tests of this nature have usually been conducted to evaluate the effects of nuclear weapons against naval vessels (such as in Operation Crossroads), or to evaluate potential sea-based nuclear weapons (such as nuclear torpedoes or depth charges). Underwater tests close to the surface can disperse large amounts of radioactive particles in water and steam, contaminating nearby ships or structures, though they generally do not create fallout other than very local to the explosion.


In the late 14th century, the first known waffle recipe was penned in an anonymous manuscript, Le Ménagier de Paris, written by a husband as a set of instructions to his young wife.[16] While it technically contains four recipes, all are a variation of the first: Beat some eggs in a bowl, season with salt and add wine. Toss in some flour, and mix. Then fill, little by little, two irons at a time with as much of the paste as a slice of cheese is large. Then close the iron and cook both sides. If the dough does not detach easily from the iron, coat it first with a piece of cloth that has been soaked in oil or grease.[17] The other three variations explain how cheese is to be placed in between two layers of batter, grated and mixed in to the batter, or left out, along with the eggs.[18] However, this was a waffle / gaufre in name only, as the recipe contained no leavening.



Detail of a French moule à oublie / moule à gaufre, Musée Lorrain

Though some have speculated that waffle irons first appeared in the 13th–14th centuries, it was not until the 15th century that a true physical distinction between the oublie and the waffle began to evolve.[8] Notably, while a recipe like the fourth in Le Ménagier de Paris was only flour, salt and wine – indistinguishable from common oublie recipes of the time – what did emerge was a new shape to many of the irons being produced. Not only were the newly fashioned ones rectangular, taking the form of the fer à hosties, but some circular oublie irons were cut down to create rectangles.[8] It was also in this period that the waffle's classic grid motif appeared clearly in a French fer à oublie and a Belgian wafelijzer – albeit in a more shallowly engraved fashion – setting the stage for the more deeply gridded irons that were about to become commonplace throughout Belgium.[19][20]



Detail from Pieter Bruegel's Het gevecht tussen Carnaval en Vasten – among the first known images of waffles

By the 16th century, paintings by Joachim de Beuckelaer, Pieter Aertsen and Pieter Bruegel clearly depict the modern waffle form.[21] Bruegel's work, in particular, not only shows waffles being cooked, but fine detail of individual waffles. In those instances, the waffle pattern can be counted as a large 12x7 grid, with cleanly squared sides, suggesting the use of a fairly thin batter, akin to our contemporary Brussels waffles (Brusselse wafels).[22]


Earliest of the 16th century waffle recipes, Om ghode waffellen te backen – from the Dutch KANTL 15 manuscript (ca. 1500–1560) – is only the second known waffle recipe after the four variants described in Le Ménagier de Paris.[23] For the first time, partial measurements were given, sugar was used, and spices were added directly to the batter: Take grated white bread. Take with that the yolk of an egg and a spoonful of pot sugar or powdered sugar. Take with that half water and half wine, and ginger and cinnamon.[24]


Alternately attributed to the 16th and 17th centuries, Groote Wafelen from the Belgian Een Antwerps kookboek was published as the first recipe to use leavening (beer yeast): Take white flour, warm cream, fresh melted butter, yeast, and mix together until the flour is no longer visible. Then add ten or twelve egg yolks. Those who do not want them to be too expensive may also add the egg white and just milk. Put the resulting dough at the fireplace for four hours to let it rise better before baking it.[25] Until this time, no recipes contained leavening and could therefore be easily cooked in the thin moule à oublies. Groote Wafelen, in its use of leavening, was the genesis of contemporary waffles and validates the use of deeper irons (wafelijzers) depicted in the Beuckelaer and Bruegel paintings of the time.[22]


Hong Kong style waffle, in Hong Kong called a "grid cake" or "grid biscuits" (格仔餅), is a waffle usually made and sold by street hawkers and eaten warm on the street.[77] It is similar to a traditional waffle but larger, round in shape and divided into four quarters. It is usually served as a snack. Butter, peanut butter and sugar are spread on one side of the cooked waffle, and then it is folded into a semicircle to eat. Eggs, sugar and evaporated milk are used in the waffle recipes, giving them a sweet flavor. They are generally soft and not dense. Traditional Hong Kong style waffles are full of the flavor of yolk. Sometimes different flavors, such as chocolate and honey melon, are used in the recipe and create various colors. Another style of Hong Kong waffle is the eggette or gai daan jai (鷄蛋仔), which have a ball-shaped pattern.


G-Flex Washers are among the industry's most advanced hard-mount washers. They offer six programmable extract speeds, including 100, 140 and 200 G-force. This offers vended laundries the ability to adjust extract speed to allow for installations over less than desirable foundations. When programmed for 200 G-force extract speeds, G-Flex Washers remove more water from each load, which reduces dry times, lowers utility usage and boosts customer turnover. Featuring the advanced ProfitPlus® Control, G-Flex Washers feature four primary cycle options: SUPERWASH, an extra-long cycle for heavy soil; HOT, for whites; WARM for colorfast and permanent press items; and COLD for colors. Customers may also add an EXTRA WASH, EXTRA RINSE and/or DELICATE CYCLE. These “extras” generate additional revenue for elevated profits! Backed by a limited 10/4/3-year ContinentalCare™ Warranty, G-Flex Washers are engineered for heavy-duty use and longevity.


Four Sisters Winery at Matarazzo Farm is a winery in White Township (mailing address is Belvidere) in Warren County, New Jersey.[2][3] A family produce farm since 1921, the vineyard was first planted in 1981, and opened to the public in 1984.[4][5] Four Sisters has 8 acres of grapes under cultivation, and produces 5,000 cases of wine per year.[6][7] The winery is so named because its owners have four daughters.[7][8]


In the 1950s and 1960s Beaulieu was considered one of the "big four" Napa Valley producers, along with Inglenook (also in Rutherford), Charles Krug, and Louis Martini.[3]


The state has four major wine-growing regions, including Lake Erie AVA on the western end of the state, the Finger Lakes AVA in the west-central area, the Hudson River Region AVA in eastern New York, and the eastern end of the Long Island AVA. In 1976, when the Farm Winery Act was passed, the Finger Lakes and Long Island regions had 19 wineries. By 1985, there were 63 wineries, and now the regions hold approximately 212 wineries.[3] The wine regions' soils originated from the last glacial advance which left gravel and shale type soils with heavy clay deposits in the Finger Lakes region and sandy soil in the Long Island region. The climate differs amongst the regions based on the Atlantic Gulf Stream and the numerous bodies of water and mountainous regions around the state. The annual precipitation ranges from 30 inches (76 cm) to 50 inches (127 cm). The growing season in the Lake Erie and Finger Lakes regions ranges from 180 to 200 days a year, while on Long Island, the season is extended to 220 days and the humidity is higher and the fall precipitation is somewhat higher as well.[5]


In Moldova four regions for wine growing are to be found:


Balti (northern zone)

Codru (central zone)

Purcari (south-eastern zone)

Cahul (southern zone)

Four Seasons Wines Limited is an Indian winery which was established in 2006,based in Bangalore, India.[1] It produces wines from grapes grown around Sahyadri valley in Maharashtra.It is a subsidiary of United Spirits Limited(USL) of the UB Group.[2] Four Seasons Wines Limited manufactures and markets wines in India. It provides red, white, and rose wines.[3] Four Seasons Wines markets its wines under the two brand names Zinzi and Four Seasons.[4]


The Four Geologic Eras

Geology is a complex and difficult subject, especially for the novice. I recommend that beginners first concentrate on the four major divisions of geologic history: the Geologic Eras. While professional and academic geologists divide the eras into periods and the periods into epochs and these into subdivisions, etc., such classification can overwhelm those who have had no formal education in the field. This blog entry thus provides a basic overview of the four Geologic Eras.


The Precambrian Era (4.6 billion years ago to 600 million years ago) encompasses the great majority of Earth's geologic history, stretching from the formation of our planet to the appearance of shelled marine life. Highlights include the formation of the oceans, the development of the atmosphere and, of course, the evolution of life. The first life forms are thought to have been chemoautotrophic bacteria, which appeared about 3.6 billion years ago.

The evolution of cyanobacteria and photosynthetic algae gradually enriched the atmosphere with oxygen and, eventually, led to the development of the vital ozone layer.


The Paleozoic Era (600 to 225 million years ago) stretches from the appearance of shelled marine life to the evolution of mammal-like reptiles. Highlights include the colonization of the land by plants and animals and the evolution of sharks, fish, insects, spiders, amphibians, ancestral reptiles, ferns and early conifers. The fern forests of this Era would later yield the vast coal deposits that fed the industrial revolution.


The Mesozoic Era (225-65 million years ago) covers the reign of dinosaurs. Other new life forms of this Era include turtles, crocodiles, ancestral birds, primitive mammals, flowering plants, snakes, lizards and social bees.


The Cenozoic Era, which continues today, began 65 million years ago. This Age of Mammals has been characterized by the spread and diversification of mammals, including the appearance of bats, whales and primates. Man belongs to the latter group but did not appear until 125,000 years ago. The last 10,000 years of the Cenozoic, following the end of the Pleistocene Ice Age, have witnessed the rise of human culture, the domestication of animals, the cultivation of plants, the development of industry and man's widespread impact on the ecosystems of our planet.


Progressing from the oldest to the current, the four major eras of Earth's geological history are Precambrian, Paleozoic, Mesozoic and Cenozoic. The lengths of these eras are often measured by the term "mya," which represents "millions of years ago." The four major eras of the geological time scale, or GTS, are also subdivided into smaller units, such as the Earth's current time scale placement within the Holocene Epoch of the Quaternary Period of the Cenozoic Era. CONTINUE READING