eto lang yata ung mga date ng homework sa com ed......................
1. july 12,2011
2. july 18,2011
3. august 9,2011
4. august 13,2011
5. august 22,2011
bale lima lang po ba ung ass?
Miyerkules, Agosto 31, 2011
Lunes, Agosto 29, 2011
vacation
hahahah................
haba ng weekend naten sarap matulog pero kakamiss kau sana may pasok na lang .........................................................................................................
haba ng weekend naten sarap matulog pero kakamiss kau sana may pasok na lang .........................................................................................................
Language camp
hahaha............................
saya ng language camp!!!!!!!!!!!!
sana maulit pa!!!!!!!!!!
saya ng language camp!!!!!!!!!!!!
sana maulit pa!!!!!!!!!!
Huwebes, Agosto 25, 2011
Miyerkules, Agosto 24, 2011
Martes, Agosto 23, 2011
Counterparts
Counterpart
Microsoft | Open Office |
Excel | Calc |
Power Point | Impress |
Paint | Draw |
Access | Base |
Math | Smart Art |
Word | Writer |
Extensions
Writer
Application Document - .sdw
Master Document - .sgl
Calc
.sdc
Impress
.sdd
Draw
.sda
Base
.sdb
Math
.smf
Writer: a decent word processor. Some people say it's better than MS Word.
Calc: the OpenOffice spreadsheet program and a replacement for MS Excel.
Impress: a presentation program that replaces MS PowerPoint.
Draw: a two- and three-dimensional drawing program that many people rate more highly than the same functions within MS Office.
MAAP
hehehehe
kapagod talaga kagabi!!!!!!!!!!!!!!
Buti na lang nakita ko na rin sa wakas ang aking kuya!!!!!!!!!!!
kapagod talaga kagabi!!!!!!!!!!!!!!
Buti na lang nakita ko na rin sa wakas ang aking kuya!!!!!!!!!!!
MAAP
RSHS FAMILY pinapakumusta nga pala kayo ni kuya Renz...........
Miss nya na daw kau.................
Miss nya na daw kau.................
earth's past
Introduction to the Archaean
3.8 to 2.5 billion years ago
It was early in the Archaean that life first appeared on Earth. Our oldest fossils date to roughly 3.5 billion years ago, and consist of bacteria microfossils. In fact, all life during the more than one billion years of the Archaean was bacterial. At right is an artist's depiction of what an Archaean coast might have looked like 3.5 billion years ago. The mounds in the foreground are stromatolites, colonies of photosynthetic bacteria which have been found as fossils in Early Archaean rocks of South Africa and Western Australia. Stromatolites increased in abundance throughout the Archaean, but began to decline during the Proterozoic. They are not common today.
 | Archaean: The Archaean occurs between the Hadean and the Proterozoic. |
Read about Tectospheric keels and plate accretion of the Archaean and Proterozoic, as studied by Paul Stoddard at Northern Illinois University.
periodical tests
hahahahahah...............
tapos na rin ang periodical !!!!!!!!!!!!!!!!!
tara galaan na....
hahahah
tapos na rin ang periodical !!!!!!!!!!!!!!!!!
tara galaan na....
hahahah
Sabado, Agosto 13, 2011
Martes, Agosto 9, 2011
august 9
hooooooooooooooooooo!!!!!!!!!!!!!!!!!!!!!!!!
saya ngayon!!!!!!!!!!!!!!!! buti naman nausog ung perio thanks .................
saya ngayon!!!!!!!!!!!!!!!! buti naman nausog ung perio thanks .................
good Working Habits
- Tap on keys and mouse gently.
- Avoid long, interrupted periods of typing.
- avoid staring at the monitor for long periods.
- Avoid long, interrupted periods of typing.
- avoid staring at the monitor for long periods.
Proper Workstation Design
- Position in a well-ventilated, comfortable room.
- Use an adjustable working chair.
- Place the monitor 16 to 24 inches.
- Use extendable legs of the keyboard.
- Place the mouse where it is easily accesible by your dominant hand.
- Use a document folder to minimize vertical head movements.
Lunes, Agosto 8, 2011
August 8
Diyos ko!!!!!!!!!!!!!!!!!!!!
Ang daming test bukas sana naman makamataas tayo neah!!!!!!!!!!!
Ang daming test bukas sana naman makamataas tayo neah!!!!!!!!!!!
How to Take Care of your PC
1. Computers need a good working temperature to work properly. They need to be placed in a cool, dry place.
2. All the cables and connectors must
be tied together to keep them away from walkways to avoid accidents.
3. Refrain from eating in front of the computer.
4. Always use an AVR to regulate electricity.
5. Do nut bump or drop the computer peripherals or components as any damage may cause them to malfunction.
6. Avoid clutter around your computer.
7. Always scan for computer viruses to avoid the cause of software malfunctions.
2. All the cables and connectors must
be tied together to keep them away from walkways to avoid accidents.
3. Refrain from eating in front of the computer.
4. Always use an AVR to regulate electricity.
5. Do nut bump or drop the computer peripherals or components as any damage may cause them to malfunction.
6. Avoid clutter around your computer.
7. Always scan for computer viruses to avoid the cause of software malfunctions.
August 8
wow!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!1
Ang saya ngayon nandito sa bahay sila Thea ............................
HAHAHAHAHAH
Ang saya ngayon nandito sa bahay sila Thea ............................
HAHAHAHAHAH
Linggo, Agosto 7, 2011
geologic time scale
The Geologic Time Scale
The study of the Earth from the beginning of time to the present has been the task of geologists who attempt to unravel the events that have shaped our planet as it is today. The Earth carries the history of geological events in its rock layers. It follows that the oldest layers are at the bottom and the youngest are at the top. With this understanding geologists are able to determine the ages of rock relative to one another. By assembling all these layers together, scientists have worked out what is known as the stratigraphic column or record of the various ages of rock. This record spans the 4.6 billion year record of Earth's history. In order to simplify the huge amount of geological information, geologists have broken Earth's history down into sections which are called geological eras, periods, and epochs. Fossils records have shown that life existed for about 3,800 million years, but complex life emerged only about 600 million years. Over time, life forms change. Their fossil record allows geologists to date and compare rocks across geological time. For example, dinosaur fossils are only found during the Mesozoic era some 245 to 65 million years ago.The following table shows the geologic time scale.
Phanerozoic Eon (544 million years ago - Present)
| ||||||
| Era | Period or System | Epoch or Series | ||||
(65 million years ago - Present)
| Quaternary (1.8 million years ago - Present)
| Holocene (8,000 years ago - Present)
| ||||
| Pleistocene (1.8 million - 8,000 years ago)
| ||||||
| Tertiary (65 - 1.8 million years ago)
| Pliocene (5.3 - 1.8 million years ago)
| |||||
| Miocene (23.8 - 5.3 million years ago)
| ||||||
| Oligocene (33.7 - 23.8 million years ago)
| ||||||
| Eocene (55.5 - 33.7 million years ago)
| ||||||
| Paleocene (65 - 55.5 million years ago)
| ||||||
| Era | Period or System | Epoch or Series | ||
| Mesozoic (248 - 65 million years ago)
| Cretaceous (145 - 65 million years ago)
| Late or Upper | ||
| Early or Lower | ||||
| Jurassic (213 - 145 million years ago)
| Late or Upper | |||
| Middle | ||||
| Early or Lower | ||||
| Triassic (248 - 213 million years ago)
| Late or Upper | |||
| Middle | ||||
| Early or Lower |
| Era | Period or System | Epoch or Series | |||
| Paleozoic (544 - 248 million years ago)
| Permian (286 - 248 million years ago)
| Late or Upper | |||
| Early or Lower | |||||
| Carboniferous (360 - 286 million years ago)
| Pennsylvanian* (325 - 286 million years ago)
| Late or Upper | |||
| Middle | |||||
| Early or Lower | |||||
| Mississippian* (360 - 325 million years ago)
| Late or Upper | ||||
| Early or Lower | |||||
| Devonian (410 - 360 million years ago)
| Late or Upper | ||||
| Middle | |||||
| Early or Lower | |||||
| Silurian (440 - 410 million years ago)
| Late or Upper | ||||
| Middle | |||||
| Early or Lower | |||||
| Ordovician (505 - 440 million years ago)
| Late or Upper | ||||
| Middle | |||||
| Early or Lower | |||||
| Cambrian (544 - 505 million years ago)
| Late or Upper | ||||
| Middle | |||||
| Early or Lower | |||||
Precambrian
(Beginning of earth - 544 million years ago)
All geologic time before the beginning of the Paleozoic era. This includes about 90% of all geologic time and spans the time from the beginning of the earth, about 4.5 billion years ago, to 544 million years ago. Its name means "before Cambrian."
mesozoic era
The Mesozoic Era
The Challenges Of Life On Land
Toward the end of the Paleozoic Era the land that would become Europe and Asia slammed into North America. By the time of the Mesozoic Era Pangea the super continent had formed. It was roughly the shape of a “C”. The huge land mass protected the Tethys Ocean which lay across tropical latitudes. Pangea and the Tethys were ringed by the Panthalassic Ocean.
Climate During The Mesozoic
The temperatures, both on land and in the ocean, were much higher than during the Paleozoic, and climates were more tropical in nature. Despite this, the seas were lower, leaving different types of land masses for life to deal with. Over all the Mesozoic Era was dryer than in the Paleozoic Era. There were more deserts and less marshland.
Within the three periods of the Mesozoic Era ( Triassic, Jurassic and Cretaceous) there were times of wide temperature and seasonal variation.
Life Recovers From The Permian Extinctions
It took most of the first and second periods of the Mesozoic, the Triassic and the Jurassic periods, for the diversity of species to recover and achieve some balance. While plant species had survived somewhat better than animals over the Permian Extinction, new types of plants developed to survive the changing conditions.
The warmer drier conditions of the Mesozoic required new reproductive methods in plants. Ferns and gymnosperms developed. Their reproductive methods allowed for good protection of the spores or seeds that would have to get through periods of drought before growing into the infant plant.
Marine LifeThe survivors of the Permian Extinction had very little competition. Corals, mollusks and fish dominated the life in the oceans. Some Reptiles took to the water to become the first air breathing hunters in the oceans. They took on a variety of forms and rose to the top of the food chain.
The Rise of The Reptiles and Dinosaurs
The dominant land animals at the end of the Permian Period were the Synapsids. This group of animals is characterized by having a single hole on each side of the skull behind the eye. They are sometimes called mammal like reptiles. This group nearly became extinct at the close of the Permian Period.
The animals that developed in the Mesozoic needed new body types to survive the extremes of temperature and moisture. Amphibians developed respiratory mechanisms that allowed them to live in or out of the water for extended periods of time. But it was the reptiles that were better adapted to the warmer dryer conditions. They developed thick, leathery skin on both their own bodies and their eggs. The reptiles thrived, dominating the landscape in both size and numbers. They are known as diapsids. Diapsids are characterized by having two openings on each side of the skull behind the eyes.
The dinosaurs evolved from these reptiles and were themselves diapsids. During the Jurassic and Cretaceous Periods the dinosaurs ruled the earth.
Both plants and animals reached giant proportions during the Mesozoic.
During the 180 million years of the Era, reptiles lived on land, in seas, and in the air. Small mammals, although not significant during the time, did exist during this era.Mass Extinction Ends The Mesozoic Era
Another mass extinction occurred at the end of the Cretaceous Period, bringing an end to the dinosaurs and the tropical forests. This extinction, while not as broad and devastating as that at the end of the Permian, had the effect of eliminating a way of life that has not been replicated.
Most researchers agree that the Mesozoic Era ended at least in part due to the impact of an asteroid.
Preceeding the Mesozoic Era is the Paleozoic Era
After the Mesozoic Era is the Cenozoic Era
cenozoic era
he Cenozoic Era (
/ˌsɛnəˈzoʊ.ɨk/ or /ˌsiːnəˈzoʊ.ɨk/; also Cænozoic or Cainozoic; meaning "new life", from Greek καινός kainos "new", and ζωή zoe "life") is the current and most recent of the three Phanerozoic geological eras and covers the period from 65.5 mya to the present. It is marked by the Cretaceous–Tertiary extinction event at the end of the Cretaceous that saw the demise of the last non-avian dinosaurs and the end of the Mesozoic Era. The Cenozoic Era is ongoing.
India collided with Asia between 55 and 45 mya; Arabia collided with Eurasia, closing the Tethys ocean, around 35 million years ago.[6]
In the earlier part of the Cenozoic, the world was dominated by the gastornid birds, terrestrial crocodiles like Pristichampsus, and a handful of primitive large mammal groups like uintatheres, mesonychids, and pantodonts. But as the forests began to recede and the climate began to cool, other mammals took over. The cenozoic is full of mammals both strange and familiar, including chalicotheres, creodonts, whales, primates, entelodonts, saber-toothed cats, mastodons and mammoths, three-toed horses, giant rhinoceros like Indricotherium, and brontotheres.
/ˌsɛnəˈzoʊ.ɨk/ or /ˌsiːnəˈzoʊ.ɨk/; also Cænozoic or Cainozoic; meaning "new life", from Greek καινός kainos "new", and ζωή zoe "life") is the current and most recent of the three Phanerozoic geological eras and covers the period from 65.5 mya to the present. It is marked by the Cretaceous–Tertiary extinction event at the end of the Cretaceous that saw the demise of the last non-avian dinosaurs and the end of the Mesozoic Era. The Cenozoic Era is ongoing. Contents[hide] |
[edit] Subdivision
The Cenozoic is divided into three periods, the Neogene, Paleogene and Quaternary.[4] The Quaternary was officially recognized by the International Commission on Stratigraphy in June 2009.[5][edit] Tectonics
Geologically, the Cenozoic is the era when the continents moved into their current positions. Australia-New Guinea, having split from Gondwana during the early Cretaceous, drifted north and, eventually, collided with South-east Asia; Antarctica moved into its current position over the South Pole; the Atlantic Ocean widened and, later in the era, South America became attached to North America.India collided with Asia between 55 and 45 mya; Arabia collided with Eurasia, closing the Tethys ocean, around 35 million years ago.[6]
[edit] Climate
The Paleocene-Eocene Thermal Maximum of 55.8 mya was a significant global warming event. However, since the Azolla event of 49 mya, the Cenozoic Era has been a period of long-term cooling. After the tectonic creation of Drake Passage, when South America fully detached from Antarctica during the Oligocene, the climate cooled significantly due to the advent of the Antarctic Circumpolar Current which brought cool deep Antarctic water to the surface. The cooling trend continued in the Miocene, with relatively short warmer periods. When South America became attached to North America creating the Isthmus of Panama, the Arctic region cooled due to the strengthening of the Humboldt and Gulf Stream currents,[7] eventually leading to the glaciations of the Pleistocene ice age, the current interglacial of which is the Holocene epoch. | This section requires expansion. |
[edit] Life
During the Cenozoic, mammals diverged from a few small, simple, generalized forms into a diverse collection of terrestrial, marine, and flying animals, giving this period its other name, the Age of Mammals, despite the fact that birds still outnumbered mammals two to one. The Cenozoic is just as much the age of savannas, the age of co-dependent flowering plants and insects, and the age of birds. Grass also played a very important role in this era, shaping the evolution of the birds and mammals that fed on it. One group that diversified significantly in the Cenozoic as well were the snakes. Evolving in the Cenozoic, the variety of snakes increased tremendously, resulting in many colubrids, following the evolution of their current primary prey source, the rodents.In the earlier part of the Cenozoic, the world was dominated by the gastornid birds, terrestrial crocodiles like Pristichampsus, and a handful of primitive large mammal groups like uintatheres, mesonychids, and pantodonts. But as the forests began to recede and the climate began to cool, other mammals took over. The cenozoic is full of mammals both strange and familiar, including chalicotheres, creodonts, whales, primates, entelodonts, saber-toothed cats, mastodons and mammoths, three-toed horses, giant rhinoceros like Indricotherium, and brontotheres.
earth's past
The Mesozoic Era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is called the Age of Dinosaurs because of its association with non-avian dinosaurs. The Chicxulub impact and other events ended the era when a majority of species on earth went extinct.
It is one of three geologic eras of the Phanerozoic eon. The division of time into eras dates back to Giovanni Arduino, in the 18th century, although his original name for the era now called the "Mesozoic" was "Secondary" (making everything after, including the modern era, the "Tertiary"; the current term Quaternary was later proposed for the modern era, following the same numbering principle). Lying between the Paleozoic and the Cenozoic, "Mesozoic" means "middle life", deriving from the Greek prefix meso-/μεσο- for "between" and zoon/ζωον meaning "animal" or "living being". It is often called the "Age of the Reptiles", after the dominant fauna of the era.
The Mesozoic was a time of tectonic, climatic and evolutionary activity. The gradual drift of the continents towards their present positions resulted in the end of the supercontinent Pangaea; this motion of the continents also provided for speciation and other important evolutionary developments. The climate was exceptionally warm throughout the period; this also played an important role in the evolution and diversification of new animal species. By the end of the era, the basis of modern life was in place.
By the end of the era, the continents had rifted into nearly their present form. Laurasia became North America and Eurasia, while Gondwana split into South America, Africa, Australia, Antarctica and the Indian subcontinent, which collided with the Asian plate during the Cenozoic, the impact giving rise to the Himalayas.
The African prosauropod Massospondylus.At the beginning of the Mesozoic Era, Africa was joined with Earth's other continents in Pangaea.[3] Africa shared the supercontinent's relatively uniform fauna which was dominated by theropods, prosauropods and primitive ornithischians by the close of the Triassic period.[3] Late Triassic fossils are found throughout Africa, but are more common in the south than north.[3] The boundary separating the Triassic and Jurassic marks the advent of an extinction event with global impact, although African strata from this time period have not been thoroughly studied.[3]
Early Jurassic strata are distributed in a similar fashion to Late Triassic beds, with more common outcrops in the south and less common fossil beds which are predominated by tracks to the north.[3] As the Jurassic proceeded, larger and more iconic groups of dinosaurs like sauropods and ornithopods proliferated in Africa.[3] Middle Jurassic strata are neither well represented nor well studied in Africa.[3] Late Jurassic strata are also poorly represented apart from the spectacular Tendaguru fauna in Tanzania.[3] The Late Jurassic life of Tendaguru is very similar to that found in western North America's Morrison Formation.[3]
Midway through the Mesozoic, about 150-160 million years ago, Madagascar separated from Africa, although it remained connected to India and the rest of the Gondwanan landmasses.[3] Fossils from Madagascar include abelisaurs and titanosaurs.[3]
The African theropod Spinosaurus, the largest known predatory land animal of all time.Later into the Early Cretaceous epoch, the India-Madagascar landmass separated from the rest of Gondwana.[3] By the Late Cretaceous, Madagascar and India had permanently split ways and continued until later reaching their modern configurations.[3]
By contrast to Madagascar, mainland Africa was relatively stable in position through-out the Mesozoic.[3] Despite the stable position, major changes occurred to its relation to other landmasses as the remains of Pangaea continued to break apart.[3] By the beginning of the Late Cretaceous epoch South America had split off from Africa, completing the southern half of the Atlantic Ocean.[3] This event had a profound effect on global climate by altering ocean currents.[3]
During the Cretaceous, Africa was populated by allosauroids and spinosaurids, including the largest known carnivorous dinosaurs.[3] Titanosaurs were significant herbivores in its ancient ecosystems.[3] Cretaceous sites are more common than Jurassic ones, but are often unable to be dated radiometrically making it difficult to know their exact ages.[3] Paleontologist Louis Jacobs, who spent time doing field work in Malawi,[4]says that African beds are "in need of more field work" and will prove to be a "fertile ground...for discovery."[3]
Sea levels began to rise during the Jurassic, which was probably caused by an increase in seafloor spreading. The formation of new crust beneath the surface displaced ocean waters by as much as 200 m (656 ft) more than today, which flooded coastal areas. Furthermore, Pangaea began to rift into smaller divisions, bringing more land area in contact with the ocean by forming the Tethys Sea. Temperatures continued to increase and began to stabilize. Humidity also increased with the proximity of water, and deserts retreated.
The climate of the Cretaceous is less certain and more widely disputed. Higher levels of carbon dioxide in the atmosphere are thought to have caused the world temperature gradient from north to south to become almost flat: temperatures were about the same across the planet. Average temperatures were also higher than today by about 10°C. In fact, by the middle Cretaceous, equatorial ocean waters (perhaps as warm as 20°C in the deep ocean) may have been too warm for sea life, and land areas near the equator may have been deserts despite their proximity to water. The circulation of oxygen to the deep ocean may also have been disrupted. For this reason, large volumes of organic matter that was unable to decompose accumulated, eventually being deposited as "black shale".
Not all of the data support these hypotheses, however. Even with the overall warmth, temperature fluctuations should have been sufficient for the presence of polar ice caps and glaciers, but there is no evidence of either. Quantitative models have also been unable to recreate the flatness of the Cretaceous temperature gradient.[citation needed]
The amount of oxygen in the Mesozoic atmosphere varied widely, but was significantly higher on average (~26%) than in today's atmosphere (20 to 21%) [5].
Recent research indicates that the specialized animals that formed complex ecosystems, with high biodiversity, complex food webs and a variety of niches, took much longer to reestablish, recovery did not begin until the start of the mid-Triassic, 4M to 6M years after the extinction[7] and was not complete until 30M years after the P-Tr extinction.[8] Animal life was then dominated, by large archosaurian reptiles: dinosaurs, pterosaurs, and aquatic reptiles such as ichthyosaurs, plesiosaurs, and mosasaurs.
The climatic changes of the late Jurassic and Cretaceous provided for further adaptive radiation. The Jurassic was the height of archosaur diversity, and the first birds and placental mammals also appeared. Angiosperms radiated sometime in the early Cretaceous, first in the tropics, but the even temperature gradient allowed them to spread toward the poles throughout the period. By the end of the Cretaceous, angiosperms dominated tree floras in many areas, although some evidence suggests that biomass was still dominated by cycad and ferns until after the KT extinction.
Some have argued that insects diversified with angiosperms because insect anatomy, especially the mouth parts, seems particularly well-suited for flowering plants. However, all major insect mouth parts preceded angiosperms and insect diversification actually slowed when they arrived, so their anatomy originally must have been suited for some other purpose.
As the temperatures in the seas increased, the larger animals of the early Mesozoic gradually began to disappear while smaller animals of all kinds, including lizards, snakes, and perhaps primates, evolved. The KT extinction exacerbated this trend. The large archosaurs became extinct, while birds and mammals thrived, as they do today.
It is one of three geologic eras of the Phanerozoic eon. The division of time into eras dates back to Giovanni Arduino, in the 18th century, although his original name for the era now called the "Mesozoic" was "Secondary" (making everything after, including the modern era, the "Tertiary"; the current term Quaternary was later proposed for the modern era, following the same numbering principle). Lying between the Paleozoic and the Cenozoic, "Mesozoic" means "middle life", deriving from the Greek prefix meso-/μεσο- for "between" and zoon/ζωον meaning "animal" or "living being". It is often called the "Age of the Reptiles", after the dominant fauna of the era.
The Mesozoic was a time of tectonic, climatic and evolutionary activity. The gradual drift of the continents towards their present positions resulted in the end of the supercontinent Pangaea; this motion of the continents also provided for speciation and other important evolutionary developments. The climate was exceptionally warm throughout the period; this also played an important role in the evolution and diversification of new animal species. By the end of the era, the basis of modern life was in place.
Contents[hide] |
[edit] Geologic periods
Following the Paleozoic, the Mesozoic extended roughly 180 million years: from 251 million years ago (Mya) to when the Cenozoic era began 65 Mya. This time frame is separated into three geologic periods. From oldest to youngest:- Triassic (251.0 Mya to 199.6 Mya)
- Jurassic (199.6 Mya to 145.5 Mya)
- Cretaceous (145.5 Mya to 65.5 Mya)
[edit] Paleogeography and tectonics
Compared to the vigorous convergent plate mountain-building of the late Paleozoic, Mesozoic tectonic deformation was comparatively mild. Nevertheless, the era featured the dramatic rifting of the supercontinent Pangaea. Pangaea gradually split into a northern continent, Laurasia, and a southern continent, Gondwana. This created the passive continental margin that characterizes most of the Atlantic coastline (such as along the U.S. East Coast) today.[2]By the end of the era, the continents had rifted into nearly their present form. Laurasia became North America and Eurasia, while Gondwana split into South America, Africa, Australia, Antarctica and the Indian subcontinent, which collided with the Asian plate during the Cenozoic, the impact giving rise to the Himalayas.
[edit] Africa
Early Jurassic strata are distributed in a similar fashion to Late Triassic beds, with more common outcrops in the south and less common fossil beds which are predominated by tracks to the north.[3] As the Jurassic proceeded, larger and more iconic groups of dinosaurs like sauropods and ornithopods proliferated in Africa.[3] Middle Jurassic strata are neither well represented nor well studied in Africa.[3] Late Jurassic strata are also poorly represented apart from the spectacular Tendaguru fauna in Tanzania.[3] The Late Jurassic life of Tendaguru is very similar to that found in western North America's Morrison Formation.[3]
Midway through the Mesozoic, about 150-160 million years ago, Madagascar separated from Africa, although it remained connected to India and the rest of the Gondwanan landmasses.[3] Fossils from Madagascar include abelisaurs and titanosaurs.[3]
By contrast to Madagascar, mainland Africa was relatively stable in position through-out the Mesozoic.[3] Despite the stable position, major changes occurred to its relation to other landmasses as the remains of Pangaea continued to break apart.[3] By the beginning of the Late Cretaceous epoch South America had split off from Africa, completing the southern half of the Atlantic Ocean.[3] This event had a profound effect on global climate by altering ocean currents.[3]
During the Cretaceous, Africa was populated by allosauroids and spinosaurids, including the largest known carnivorous dinosaurs.[3] Titanosaurs were significant herbivores in its ancient ecosystems.[3] Cretaceous sites are more common than Jurassic ones, but are often unable to be dated radiometrically making it difficult to know their exact ages.[3] Paleontologist Louis Jacobs, who spent time doing field work in Malawi,[4]says that African beds are "in need of more field work" and will prove to be a "fertile ground...for discovery."[3]
[edit] Climate
The Triassic was generally dry, a trend that began in the late Carboniferous, and highly seasonal, especially in the interior of Pangaea. Low sea levels may have also exacerbated temperature extremes. With its high specific heat capacity, water acts as a temperature-stabilizing heat reservoir, and land areas near large bodies of water—especially the oceans—experience less variation in temperature. Because much of the land that constituted Pangaea was distant from the oceans, temperatures fluctuated greatly, and the interior of Pangaea probably included expansive areas of desert. Abundant evidence of red beds and evaporites such as salt support these conclusions.Sea levels began to rise during the Jurassic, which was probably caused by an increase in seafloor spreading. The formation of new crust beneath the surface displaced ocean waters by as much as 200 m (656 ft) more than today, which flooded coastal areas. Furthermore, Pangaea began to rift into smaller divisions, bringing more land area in contact with the ocean by forming the Tethys Sea. Temperatures continued to increase and began to stabilize. Humidity also increased with the proximity of water, and deserts retreated.
The climate of the Cretaceous is less certain and more widely disputed. Higher levels of carbon dioxide in the atmosphere are thought to have caused the world temperature gradient from north to south to become almost flat: temperatures were about the same across the planet. Average temperatures were also higher than today by about 10°C. In fact, by the middle Cretaceous, equatorial ocean waters (perhaps as warm as 20°C in the deep ocean) may have been too warm for sea life, and land areas near the equator may have been deserts despite their proximity to water. The circulation of oxygen to the deep ocean may also have been disrupted. For this reason, large volumes of organic matter that was unable to decompose accumulated, eventually being deposited as "black shale".
Not all of the data support these hypotheses, however. Even with the overall warmth, temperature fluctuations should have been sufficient for the presence of polar ice caps and glaciers, but there is no evidence of either. Quantitative models have also been unable to recreate the flatness of the Cretaceous temperature gradient.[citation needed]
The amount of oxygen in the Mesozoic atmosphere varied widely, but was significantly higher on average (~26%) than in today's atmosphere (20 to 21%) [5].
[edit] Life
The extinction of nearly all animal species at the end of the Permian period allowed for the radiation of many new lifeforms. In particular, the extinction of the large herbivorous and carnivorous dinocephalia left those ecological niches empty. Some were filled by the surviving cynodonts and dicynodonts, the latter of which subsequently became extinct. Some plant species had distributions that were markedly different from succeeding periods; for example, the Schizeales, a fern order, were skewed to the Northern Hemisphere in the Mesozoic, but are now better represented in the Southern Hemisphere.[6]Recent research indicates that the specialized animals that formed complex ecosystems, with high biodiversity, complex food webs and a variety of niches, took much longer to reestablish, recovery did not begin until the start of the mid-Triassic, 4M to 6M years after the extinction[7] and was not complete until 30M years after the P-Tr extinction.[8] Animal life was then dominated, by large archosaurian reptiles: dinosaurs, pterosaurs, and aquatic reptiles such as ichthyosaurs, plesiosaurs, and mosasaurs.
The climatic changes of the late Jurassic and Cretaceous provided for further adaptive radiation. The Jurassic was the height of archosaur diversity, and the first birds and placental mammals also appeared. Angiosperms radiated sometime in the early Cretaceous, first in the tropics, but the even temperature gradient allowed them to spread toward the poles throughout the period. By the end of the Cretaceous, angiosperms dominated tree floras in many areas, although some evidence suggests that biomass was still dominated by cycad and ferns until after the KT extinction.
Some have argued that insects diversified with angiosperms because insect anatomy, especially the mouth parts, seems particularly well-suited for flowering plants. However, all major insect mouth parts preceded angiosperms and insect diversification actually slowed when they arrived, so their anatomy originally must have been suited for some other purpose.
As the temperatures in the seas increased, the larger animals of the early Mesozoic gradually began to disappear while smaller animals of all kinds, including lizards, snakes, and perhaps primates, evolved. The KT extinction exacerbated this trend. The large archosaurs became extinct, while birds and mammals thrived, as they do today.
earth's past
he Paleozoic or Palaeozoic Era (from the Greek palaios (παλαιός), "old" and zoe (ζωή), "life", meaning "ancient life") is the earliest of three geologic eras of the Phanerozoic Eon. The Paleozoic spanned from roughly 542 to 251 million years ago (ICS, 2004), and is subdivided into six geologic periods; from oldest to youngest they are: the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian. Fish populations exploded in the Devonian. During the late Paleozoic, great forests of primitive plants thrived on land forming the great coal beds of Europe and eastern North America. By the end of the era, the first large, sophisticated reptiles and the first modern plants, (conifers) had developed.
The Paleozoic Era ended with the largest mass extinction in Earth's history, the Permian-Triassic Extinction Event. The effects of this catastrophe were so devastating that it took life on land 30 million years to recover.[1] Recovery of life in the sea may have been much faster.[2]
In North America, the era began with submerged geosynclines, or deep basins of the Earth's crust, along the eastern, southeastern, and western sides of the continent, while the interior was dry land. As the era proceeded, the marginal seas periodically washed over the stable interior, leaving sedimentary deposits to mark their incursions. During the early part of the era, the area of exposed Precambrian, or shield, rocks in central Canada were eroding, supplying sediment to the geosynclines from the interior. Beginning in the Ordovician Period, mountain building intermittently proceeded in the eastern part of the Appalachian geosyncline throughout the rest of the era, bringing in new sediments. Sediments washing from the Acadian Mountains filled the western part of the Appalachian geosyncline to form the famous coal swamps of the Carboniferous Period.
Paleoclimatic studies and evidence of glaciers indicate that central Africa was most likely in the polar regions during the early Paleozoic. During the early Paleozoic, the huge continent Gondwanaland had either formed or was forming. By mid-Paleozoic, the collision of North America and Europe produced the Acadian-Caledonian uplifts, and a subduction plate uplifted eastern Australia. By the late Paleozoic, continental collisions formed the supercontinent Pangaea and resulted in some of the great mountain chains, including the Appalachians, Urals, and mountains of Tasmania.
Amphibians were the dominant vertebrates until the mid Carboniferous, then climate change greatly reduced their diversity; meanwhile reptiles prospered and continued to increase in number and variety by the late Permian.[3]
Geologically, the Paleozoic starts shortly after the breakup of a supercontinent called Pannotia and at the end of the global Varanger glaciation and Snowball Earth). Throughout the early Paleozoic, the Earth's landmass was broken up into a substantial number of relatively small continents. Toward the end of the era, the continents gathered together into a supercontinent called Pangaea, which included most of the Earth's land area.
Land distribution in the Early Paleozoic, 514 MaThe Early Cambrian climate was probably moderate at first, becoming warmer over the course of the Cambrian, as the second-greatest sustained sea level rise in the Phanerozoic got underway. However, as if to offset this trend, Gondwana moved south with considerable speed, so that, in Ordovician time, most of West Gondwana (Africa and South America) lay directly over the South Pole. The Early Paleozoic climate was also strongly zonal, with the result that the "climate", in an abstract sense became warmer, but the living space of most organisms of the time—the continental shelf marine environment—became steadily colder. However, Baltica (Northern Europe and Russia) and Laurentia (eastern North America and Greenland) remained in the tropical zone, while China and Australia lay in waters which were at least temperate. The Early Paleozoic ended, rather abruptly, with the short, but apparently severe, Late Ordovician Ice Age. This cold spell caused the second-greatest mass extinction of Phanerozoic time. Over time, the warmer weather moved into the Paleozoic era.
The Middle Paleozoic was a time of considerable stability. Sea levels had dropped coincident with the Ice Age, but slowly recovered over the course of the Silurian and Devonian. The slow merger of Baltica and Laurentia, and the northward movement of bits and pieces of Gondwana created numerous new regions of relatively warm, shallow sea floor. As plants took hold on the continental margins, oxygen levels increased and carbon dioxide dropped, although much less dramatically. The north-south temperature gradient also seems to have moderated, or metazoan life simply became hardier, or both. At any event, the far southern continental margins of Antarctica and West Gondwana became increasingly less barren. The Devonian ended with a series of turnover pulses which killed off much of Middle Paleozoic vertebrate life, without noticeably reducing species diversity overall.
The Late Paleozoic was a time which has left us a good many unanswered questions. The Mississippian epoch began with a spike in atmospheric oxygen, while carbon dioxide plummeted to unheard-of lows. This destabilized the climate and led to one, and perhaps two, ice ages during the Carboniferous. These were far more severe than the brief Late Ordovician Ice; but, this time, the effects on world biota were inconsequential. By the Cisuralian, both oxygen and carbon dioxide had recovered to more normal levels. On the other hand, the assembly of Pangea created huge arid inland areas subject to temperature extremes. The Lopingian is associated with falling sea levels, increased carbon dioxide and general climatic deterioration, culminating in the devastation of the Permian extinction.
The Paleozoic Era ended with the largest mass extinction in Earth's history, the Permian-Triassic Extinction Event. The effects of this catastrophe were so devastating that it took life on land 30 million years to recover.[1] Recovery of life in the sea may have been much faster.[2]
Contents[hide] |
[edit] Geology
During the hiatus between the late Precambrian and the Paleozoic most of the evidence of the earth's early history was destroyed by erosion.[citation needed] From the beginning of the Paleozoic, shallow seas began to encroach on the continents, large parts of North America were completely submerged.In North America, the era began with submerged geosynclines, or deep basins of the Earth's crust, along the eastern, southeastern, and western sides of the continent, while the interior was dry land. As the era proceeded, the marginal seas periodically washed over the stable interior, leaving sedimentary deposits to mark their incursions. During the early part of the era, the area of exposed Precambrian, or shield, rocks in central Canada were eroding, supplying sediment to the geosynclines from the interior. Beginning in the Ordovician Period, mountain building intermittently proceeded in the eastern part of the Appalachian geosyncline throughout the rest of the era, bringing in new sediments. Sediments washing from the Acadian Mountains filled the western part of the Appalachian geosyncline to form the famous coal swamps of the Carboniferous Period.
Paleoclimatic studies and evidence of glaciers indicate that central Africa was most likely in the polar regions during the early Paleozoic. During the early Paleozoic, the huge continent Gondwanaland had either formed or was forming. By mid-Paleozoic, the collision of North America and Europe produced the Acadian-Caledonian uplifts, and a subduction plate uplifted eastern Australia. By the late Paleozoic, continental collisions formed the supercontinent Pangaea and resulted in some of the great mountain chains, including the Appalachians, Urals, and mountains of Tasmania.
[edit] Animal Life
A noteworthy feature of Paleozoic life is the sudden appearance of nearly all of the invertebrate animal phyla in great abundance at the beginning of the Cambrian. A few primitive fishlike invertebrates, and then vertebrates, appeared in the Cambrian and Ordovician, scorpions in the Silurian period, land invertebrates and amphibians in the Devonian, land reptiles in the Carboniferous, and marine reptiles in the Permian.Amphibians were the dominant vertebrates until the mid Carboniferous, then climate change greatly reduced their diversity; meanwhile reptiles prospered and continued to increase in number and variety by the late Permian.[3]
[edit] Plant Life
Plant life of the Paleozoic era reached its climax in the Carboniferous, when towering lycopsid rainforests dominated the tropical belt of Euramerica. Climate change caused the Carboniferous Rainforest Collapse which fragmented this habitat, diminishing the diversity of plant life in the late Carboniferous and Permian.[3][edit] Tectonics
[edit] Climate
The Ordovician and Silurian periods were warm greenhouse periods, with the highest sea levels of the Paleozoic (200 m above today's); the warm climate was interrupted only by a ~30 Ma cool period, the Early Palaeozoic Icehouse, culminating in the Hirnantian glaciation.[4]  | This section does not cite any references or sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed. (July 2007) |
The Middle Paleozoic was a time of considerable stability. Sea levels had dropped coincident with the Ice Age, but slowly recovered over the course of the Silurian and Devonian. The slow merger of Baltica and Laurentia, and the northward movement of bits and pieces of Gondwana created numerous new regions of relatively warm, shallow sea floor. As plants took hold on the continental margins, oxygen levels increased and carbon dioxide dropped, although much less dramatically. The north-south temperature gradient also seems to have moderated, or metazoan life simply became hardier, or both. At any event, the far southern continental margins of Antarctica and West Gondwana became increasingly less barren. The Devonian ended with a series of turnover pulses which killed off much of Middle Paleozoic vertebrate life, without noticeably reducing species diversity overall.
The Late Paleozoic was a time which has left us a good many unanswered questions. The Mississippian epoch began with a spike in atmospheric oxygen, while carbon dioxide plummeted to unheard-of lows. This destabilized the climate and led to one, and perhaps two, ice ages during the Carboniferous. These were far more severe than the brief Late Ordovician Ice; but, this time, the effects on world biota were inconsequential. By the Cisuralian, both oxygen and carbon dioxide had recovered to more normal levels. On the other hand, the assembly of Pangea created huge arid inland areas subject to temperature extremes. The Lopingian is associated with falling sea levels, increased carbon dioxide and general climatic deterioration, culminating in the devastation of the Permian extinction.
[edit] See also
 | Wikimedia Commons has media related to: Paleozoic |
[edit] References and further reading
- ^ Sahney, S. and Benton, M.J. (2008). "Recovery from the most profound mass extinction of all time" (PDF). Proceedings of the Royal Society: Biological 275 (1636): 759–65. doi:10.1098/rspb.2007.1370. PMC 2596898. PMID 18198148. http://journals.royalsociety.org/content/qq5un1810k7605h5/fulltext.pdf.
- ^ url=http://www.economist.com/node/16524904
- ^ a b Sahney, S., Benton, M.J. & Falcon-Lang, H.J. (2010). "Rainforest collapse triggered Pennsylvanian tetrapod diversification in Euramerica" (PDF). Geology 38 (12): 1079–1082. doi:10.1130/G31182.1. http://geology.geoscienceworld.org/cgi/content/abstract/38/12/1079.
- ^ Munnecke, A.; Calner, M.; Harper, D. A. T.; Servais, T. (2010). "Ordovician and Silurian sea-water chemistry, sea level, and climate: A synopsis". Palaeogeography, Palaeoclimatology, Palaeoecology 296 (3–4): 389–413. doi:10.1016/j.palaeo.2010.08.001.
- British Palaeozoic Fossils, 1975, The Natural History Museum, London.
- "International Commission on Stratigraphy (ICS)". Home Page. http://www.stratigraphy.org/. Retrieved September 19, 2005.
| Preceded by Proterozoic Eon | 542 Ma - Phanerozoic Eon - Present | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 542 Ma - Paleozoic Era - 251 Ma | 251 Ma - Mesozoic Era - 65 Ma | 65 Ma - Cenozoic Era - Present | ||||||||||
| Cambrian | Ordovician | Silurian | Devonian | Carboniferous | Permian | Triassic | Jurassic | Cretaceous | Paleogene | Neogene | Quaternary | |
| ||
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