Paleozoic Era

Prepared by: Louis Bautista and Van Salvador CAMBRIAN PERIOD

The Cambrian Period marks an important point in the history of life on Earth; it is the time when most of the major groups of animals first appear in the fossil record. This event is sometimes called the "Cambrian Explosion," because of the relatively short time over which this diversity of forms appears. It was once thought that Cambrian rocks contained the first and oldest fossil animals, but these are now found in the earlier Ediacaran (Vendian) strata. CAMBRIAN PERIOD

Cambrian is the name given to a period of time in Earth's history (i.e., Cambrian Period), which spanned 570 - 510 million years ago. The proper name Cambrian is also given to all the rocks that formed during that time (i.e., Cambrian System). In other words, the Cambrian System is the rock record of events that occurred and organisms that lived during an interval of geological time called Cambrian Period. Cambrian is the initial period of the Paleozoic Era.

During Cambrian, the breakup of the supercontinent of Gondwana began with the separation of some landmasses including part of Asia and the ancient continents called Baltica and Laurentia (i.e., proto-North America). During its separation from the main Gondwana land mass, Laurentia had a collision with the southern end of what is now South America (specifically western Argentina), which resulted in some crustal deformation and mountain building. At this time, there was essentially a single world ocean, which is referred to as Panthalassa.

MOVEMENT OF PLATE TECTONICS The continental plate movement and collisions during this period generated pressure and heat between continents. this resulted in the folding, faulting, and crumpling of rock which formed large mountain ranges.

ORGANISMS Almost every metazoan phylum with hard parts, and many that lack hard parts, made its first appearance in the Cambrian. The only modern phylum with an adequate fossil record to appear after the Cambrian was the phylum Bryozoa, which is not known before the early Ordovician. A few mineralized animal fossils, including sponge spicules and probable worm tubes, are known from the Ediacaran Period immediately preceding the Cambrian.

Some of the odd fossils of the biota from the Ediacaran may also have been animals representative of living phyla, although this remains a somewhat controversial topic. However, the Cambrian was nonetheless a time of great evolutionary innovation, with many major groups of organisms appearing within a span of only forty million years.

Trace fossils made by animals also show increased diversity in Cambrian rocks, showing that the animals of the Cambrian were developing new ecological niches and strategies — such as active hunting, burrowing deeply into sediment, and making complex branching burrows. Finally, the Cambrian saw the appearance and/or diversification of mineralized algae of various types, such as the coralline red algae and the dasyclad green algae.

Cambrian was a time of rising global temperatures and Cambrian global climate ultimately became warmer than today. During Cambrian, there were essentially no polar or high-altitude Glaciers. Further, there were no continents located at polar positions. The Cambrian Earth likely had more equitable climates than present because of the large amount of surficial seawater (approximately 85% or more, compared to approximately 70% at present) and lack of significant topographic relief. CLIMATE

Winds were likely confined to rather well-defined belts, and there is good evidence of persistent trade winds preserved in vast cross-bedded Cambrian sandstones. The end of Cambrian came gradually with falling sea levels and the onset of slightly cooler global temperatures.

WATER FEATURES During most of Cambrian, global sea levels were at relatively high elevations as compared with most of the balance of Earth's history. The world's continents were mainly low-lying deserts and alluvial plains, and the rising Cambrian seaâin what is known as the Sauk transgressionâencroached upon these areas, thus forming vast epicontinental seas.

GEOLOGIC FACTORS Cambrian life on land was probably quite limited. There is evidence that stromatolitic growth of blue-green algae and bacteria covered rocks and formed sediment layers at or near oceanic shorelines and lake margins. However, complex life forms are not found in Cambrian terrestrial sediments. It is possible that some arthropods may have lived partially or entirely upon land at this time, but this is speculative in the absence of fossil evidence. 10% of that found in the modern atmosphere.

There were no land plants at this time, and thus Cambrian landscapes were at the mercy of wind and water erosion without any protection from vegetation. The minimal level of photosynthetic activity before and during Cambrian raised oxygen levels in Earth's atmosphere.

The most famous of fossil localities with such Cambrian fossils is at Mount Wapta, British Columbia, Canada (i.e., Burgess Shale outcrops). In these strata, the earliest known chordate (spinal cord-bearing animal), Pikaia , was first found.

ORDOVICIAN PERIOD Prepared by: Ricky Perez and Kyle Galiluyo

ORDOVICIAN PERIOD The Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 41.7 to 443.7±1.5 MYA . It follows the Cambrian Period and is followed by the Silurian Period. The Ordovician, named after the Celtic tribe of the Ordovices, was defined by Charles Lapworth in 1879

EVENTS THAT HAPPENED Life continued to flourish during the Ordovician as it did in the Cambrian, although the end of the period was marked by a significant mass extinction. Invertebrates, namely mollusks and arthropods, dominated the oceans. Fish, the world's first true vertebrates, continued to evolve, and those with jaws may have first appeared late in the period. Life had yet to diversify on land.

The Ordovician Period started at a major extinction event called the Cambrian–Ordovician extinction events some time about 488.3 ± 1.7 Mya (million years ago), and lasted for about 44.6 million years. It ended with the Ordovician–Silurian extinction event, about 443.7 ± 1.5 Mya (ICS, 2004) that wiped out 60% of marine genera.

ORGANISMS Invertebrate life became increasingly diverse and complex through the Ordovician. Both calcareous and siliceous sponges are known; among other types, the stromatoporoids first appeared in the Ordovician.

CALCAREOUS AND SILICEOUS SPONGES

Tabulata and Rugosa first appeared in the Ordovician, the solitary or horn corals being especially distinctive. Bryozoans and brachiopods were a dominant component of many assemblages. mollusks were also common and included the gastropods, monoplacophorans, bivalves, cephalopods, chits, scaphopods, and rostroconchs.

The fossil record of Ordovician annelids consists chiefly of small, calcareous tubes, tiny jaws made up of phosphate material, and trace fossils.Trilobites are common and diverse in Ordovician strata but do not dominate assemblages as they did in the Cambrian Period. Ordovician arthropods are also represented by the ostacods as well as by much rarer forms such as branchiopods, barnacles, phyllocarid shrimp, aglaspids, and eurypterids.

ECHINODERMS Echinoderms reached their peak diversity of 20 classes during the Ordovician, with crinoids , cystoids, asteroids, edrioasteroids and homalozoans being the most common. Graptolites and conodonts are among the most important fossils in the Ordovician for correlating, or demonstrating age equivalence between, different layers of rock.

MICROFOSSILS AND PLANKTONS Ordovician seas were characterized by a rich and diverse assemblage of species. Calcified microbial mats, known as stromatolites, are found in Ordovician rocks, although they are not as common there as in strata from the Proterozoic Eon and Cambrian Period. Chitinozoans or acritarchs, microfossils with a hollow cavity and organic walls, represent the phytoplankton.

Ordovician foraminiferans include both agglutinated and calcareous forms, including the first fusulinids (single-celled, amoeba-like organisms with complex shells). The siliceous that lived as zooplankton are also found in Ordovician rocks.

The food chain became more complicated as new varieties of life occurred. New life forms includes true corals, nautiloids, starfish, brachiopods, etc. Conodonts (small, eel-like creatures) became common and their fossils serve as markers in the rock layers greatly aiding paleontologists in their efforts to determine the different ages of the rocks

CLIMATE At the beginning of the period, around 480 million years ago, the climate was very hot due to high levels of CO2, which gave a strong greenhouse effect. The marine waters are assumed to have been around 45°C, which restricted the diversification of complex multi-cellular organisms. But over time, the climate become cooler, and around 460 million years ago, the ocean temperatures became comparable to those of present day equatorial waters.

As with North America and Europe, Gondwana was largely covered with shallow seas during the Ordovician. Shallow clear waters over continental shelves encouraged the growth of organisms that deposit calcium carbonates in their shells and hard parts. The Panthalassic Ocean covered much of the northern hemisphere, and other minor oceans included Proto-Tethys, Paleo-Tethys, Khanty Ocean, which was closed off by the Late Ordovician, Iapetus Ocean, and the new Rheic Ocean.

As the Ordovician progressed, we see evidence of glaciers on the land we now know as Africa and South America. At the time these land masses were sitting at the South Pole, and covered by ice caps.

GEOLOGIC FACTORS Much of it was submerged underwater During the Ordovician the first plants appeared. The seas receded from their high points The seas reached the highest point ever recorded

The supercontinent Gondwana drifted slowly southward towards the South Pole: having begun its journey in tropic latitudes, it gradually accumulated glaciers as it arrived in cooler regions. This heralded a 20-million-year ice age during which shallow, life-rich seas shrank away with sea levels rising as much as 1,970 feet (600 meters) above those of today.

WATER FEATURES The Ordovician saw the highest sea levels of the Paleozoic, and the low relief of the continents led to many shelf deposits being formed under hundreds of metres of water. Sea level rose more or less continuously throughout the Early Ordovician, levelling off somewhat during the middle of the period. Locally, some regressions occurred, but sea level rise continued in the beginning of the Late Ordovician.

A change was soon on the cards, however, and sea levels fell steadily in accord with the cooling temperatures for the ~30 million years leading up to the Hirnantian glaciation. Within this icy stage, sea level seems to have risen and dropped somewhat, but despite much study the details remain unresolved.

Silurian Period Prepared by: Russen Galano, Christine Agua and Jewel Potenciano

SILURIAN PERIOD The Silurian Period begins 435 million years ago and spans 23 million years ago. The Silurian Period is named after the ”Silures”, an ancient British tribe which inhabited the Welsh Borderland during the Roman times.

MAJOR EVENTS As with other geologic periods, the rock beds that define the period's start and end are well identified, but the exact dates are uncertain by several million years. The base of the Silurian is set at a major extinction event when 60% of marine species were wiped out.

MOVEMENT OF PLATE TECTONICS During the Silurian, Gondwana continued a slow southward drift to high southern latitudes, but there is evidence that the Silurian icecaps were less extensive than those of the late Ordovician glaciation. The southern continents remained united during this period.

The melting of icecaps and glaciers contributed to a rise in sea level, recognizable from the fact that Silurian sediments overlie eroded Ordovician sediments, forming an unconformity. The continents of Avalonia, Baltica, and Laurentia drifted together near the equator, starting the formation of a second supercontinent known as Euramerica.

ORGANISMS All animal life still lived in the seas. A significant evolutionary milestone during the Silurian was the appearance of jawed and bony fish. Life also began to appear on land in the form of small, moss-like, vascular plants which grew beside lakes, streams, and coastlines. However, terrestrial life would not greatly diversify and impact the landscape until the Devonian.

NAUTILOIDS The Nautiloids decreased greatly in number, and those surviving had coiled and frilled shells.

CRINOIDS Crinoids, many beautifully colored, still waved about on their stalks in response to the sea currents.

KING CRABS KING CRABS APPEARED, AND THEY HAVE CHANGED BUT LITTLE IN ALL HUNDREDS OF MILLIONS OF YEARS FROM SILURIAN PERIOD TO PRESENT.

TRILOBITES Some Trilobites crawled on the sea bottom. Trilobites are animals that got their name because their bodies were formed in three lobes; that is they were trilobed.

PLACEODERMS Paleceoderms are armored by their extensive dermal skeleton. These dermal bones (or plates) form head and thoracic shields that are either articulated by distinctive joints or fused into a single unit. Pectoral fins are typically well developed. Bony shearing or crushing structures on the jaws substitute for true teeth, which are absent. The jaw joint is simple.

BRACHIOPODS Brachiopods are a phylum of marine animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs.

BRYOZOA The Bryozoa, also known as Ectoprocta or commonly as moss animals, are a phylum of aquatic invertebrate animals.

MOLLUSCA The Mollusca, common name molluscs or mollusks, is a large phylum of invertebrate animals.

HEDERELLIDS Hederellids are extinct colonial animals with calcitic tubular branching exoskeletons.

LEECHES Leeches also made their appearance during the Silurian Period. Leeches are segmented worms that belong to the phylum Annelida and comprise the subclass Hirudinea.

EURYPTERID But the form of life that dominated this period was the eurypterid also known as sea scorpion. These sea-living animals looked very much like the scorpions that live on land today. There were many kinds of sea scorpions, varying in length from two-inch pygmies to nine-foot giants.

COOKSONIA Cooksonia, the earliest vascular plant, was formed in the middle Silurian.

CLIMATE The Silurian period enjoyed relatively stable and warm temperatures, in contrast with the extreme glaciations of the Ordovician before it, and the extreme heat of the ensuing Devonian.

Sea levels rose from their Hirnantian low throughout the first half of the Silurian; they subsequently fell throughout the rest of the period, although smaller scale patterns are superimposed on this general trend; fifteen high-stands can be identified, and the highest Silurian sea level was probably around 140 m higher than the lowest level reached.

During this period, the Earth entered a long warm greenhouse phase, and warm shallow seas covered much of the equatorial land masses. Early in the Silurian, glaciers retreated back into the South Pole until they almost disappeared in the middle of Silurian. The period witnessed a relative stabilization of the Earth's general climate, ending the previous pattern of erratic climatic fluctuations.

Layers of broken shells (called coquina) provide strong evidence of a climate dominated by violent storms generated then as now by warm sea surfaces. Later in the Silurian, the climate cooled slightly, but in the Silurian-Devonian boundary, the climate became warmer

The period witnessed a relative stabilization of the Earth's general climate, ending the previous pattern of erratic climatic fluctuations. Layers of broken shells (called coquina) provide strong evidence of a climate dominated by violent storms generated then as now by warm sea surfaces. Later in the Silurian, the climate cooled slightly, but in the Silurian-Devonian boundary, the climate became warmer.

Glaciers formed 430 million years ago. They may have only lasted one or a few million years. During this time, ice covered the northern part of Africa, which was located over the South Pole.

Climate models have been used to help understand weather and regional climates of the supercontinent Pangaea. The models suggest that monsoons affected the subtropical east coast and that interior of Pangaea was dry.

Did You Know? The length of a year has not always been 365 days. During the early Silurian Period, it has been calculated that a year lasted 421 days. By the Middle Devonian Period 100 million years later, it had decreased to 410 days per year. This downward trend would continue until we reached our present number of days (365.25)

GEOLOGY AND CLIMATE During the Silurian, Earth underwent considerable changes that had important repercussions for the environment and life within it. Plate tectonic activity continued to shift the continents during the Silurian. The great southern continent of Gondwana drifted farther across the South Pole, while Siberia, Laurentia and Baltica clustered around the equator.Laurentia and Baltica collided at the end of the Silurian, forming a new supercontinent, Euramerica, and raising new mountain ranges. Rising sea level formed a nearly continuous sea from New York to Nevada, and other shallow seas still covered parts of other continents.

The Early Silurian was also a time of global icehouse climate that included great ice sheets at high latitudes. By the middle of the Silurian, however, global climate had become much warmer, comparable to that of most of the Ordovician and Devonian Periods. A new greenhouse phase began, leading to the melting of many large glacial ice sheets, which contributed to a substantial rise in global sea level.

The result was a world with distinct north-south climatic zones, much as today. Glaciers remained at high latitudes, but lower latitudes were relatively warm and arid conditions led to the formation of extensive evaporite (salt) deposits near the equator.

GEOLOGIC FACTORS The geographically two continents were found totally interlocked, the northern Laurasia and the southern part called the Gondwana, alternatively both parts were submerged underwater. The North Pole was somewhere near the northern Pacific Ocean and the South Pole somewhere near southwestern Africa. The equator passed over the southeastern Europe over the northern Australia and Greenland to the center of America

WATER FEATURES The Silurian period enjoyed relatively stable and warm temperatures, in contrast with the extreme glaciations of the Ordovician before it, and the extreme heat of the ensuing Devonian. Sea levels rose from their Hirnantian low throughout the first half of the Silurian; they subsequently fell throughout the rest of the period, although smaller scale patterns are superimposed on this general trend; fifteen high-stands can be identified, and the highest Silurian sea level was probably around 140 m higher than the lowest level reached.

Paleozoic Era

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