The name ‘Cambrian Explosion’ refers to a period in Earth’s history where an unusually large number of new lifeforms developed over a relatively short amount of time.The climate of the Cambrian period was generally very mild. The majority of the Earth’s landmasses were clustered on a single continent, which made up a large portion of Pangaea.In terms of temperature, the average yearly range would have been between 50 degrees F to 68 degrees F (10 degrees C to 20 degrees C). Conventional wisdom says that the main cause of the Cambrian Explosion was an increase in oxygen. But new research, including some performed by geologist Donald Prothero and biologist Elen Shcherbakov, suggests that methane emissions may have been behind the rise of atmospheric oxygen, and the sudden diversification of life forms. This led to the mass extinction of Cambrian organisms and other little life. The pika formation of middle Cambrian stromatolites near Banff National Park, Helen Lake, Canada was a period when trilobites were abundant. One of the many invertebrates of the period, Anomalocaris, was an ancient aquatic killer. The pikaia had an unusual body plan, while the opabinia was another marine creature with a unique body structure.Events That Happened During The Cambrian PeriodThe Cambrian period is the first geological period of the Paleozoic Era that occurred between 541 and 485 million years ago. It was during this time that most of the major animal phyla and multicellular life appeared.Little is known about what may have caused such rapid evolution, but it could be because many marine organisms evolved hard parts (shells or exoskeletons) to protect themselves against predators.Another possible explanation for the diversification of lifeforms during this era is an exceptionally high level of oxygen in the Earth’s atmosphere.However, not much evidence exists to support this claim. Insects developed wings, allowing them to float on air currents and fly, around 400 million years ago.The world’s oceans during the Cambrian period were much higher than they are today.This is because glaciers had built up on the Earth’s surface until their weight became so great that they broke off, causing huge floods in surrounding areas.As a result of these floods, many new ecosystems developed with high biodiversity levels.Many Paleozoic rocks formed during this period are still exposed at the Earth’s surface, or have only been covered by younger sedimentary layers since then; thus, unlike most geological periods, it was not completely underwater.Glacial activity added large amounts of calcium to the Earth’s oceans, which caused marine organisms to develop shells and exoskeletons made out of calcium carbonate (CaCO3).The atmosphere contained very little oxygen. The Cambrian period is where we see the first appearance of most major animal phyla.Cambrian animals, or Cambrian organisms, developed from tiny, immobile forms into more complex organisms with legs and jaws to catch prey.Early arthropods, mollusks, echinoderms, and chordates appeared in these fossil beds dating between 541 and 485 million years ago.These important fossils have allowed scientists to reconstruct the ‘Tree Of Life’ - a diagram representing all living things - by studying which groups share certain characteristics.The first vertebrates, or marine animals, emerged during this period, as well as many invertebrate groups, including hard-shelled marine invertebrates such as brachiopods, echinoderms (such as starfish, sea urchins, and crinoids), mollusks (including the extinct bellerophontids), sponges, tentaculitoid microconchids (a type of worm), and trilobites.The reason why these groups emerged during this period is that calcification became popular among marine organisms—hard outer parts were used to protect their bodies from predators and complex life.Although arthropods also developed exoskeletons made out of chitin for protection, most did not contribute significantly to the Cambrian Explosion.During this time, life on land consisted of only microbial life that laid down chlorophyll-containing bacterial films in coastal lagoons.Around 580 million years ago, more complex terrestrial ecosystems were formed and fossilized in the form of microbial mats and traces of burrows.The Cambrian period can be dated by distinctive fossil traces found between 541 and 485 million years ago. Trace fossil, or fossil evidence, includes tracks, trails, burrows, or even coprolites (fossil feces).These trace fossils reveal that organisms such as arthropods and annelids were able to extend their habitats beyond shallow marine environments into intertidal zones during the Cambrian period.An interesting aspect of this period’s fossil traces is that it has very few invertebrate groups compared to later periods, like the Silurian and Devonian, which both contain large numbers of trilobite fossils.Scientists continue to examine these fossil beds to correctly assemble the ‘Tree Of Life’, which, so far, contains 15 main branches. Today’s modern oceans are very different from what they were during the Cambrian period.The composition of ocean organisms changed over time. Back then, marine organisms and other animal life possessed calcium carbonate exoskeletons that would appear in all five major stages (Cambrian to Quaternary).It is only during the Cenozoic Era that these skeletons began to fade away, because levels of calcium increased while oxygen decreased, around 145 million years ago, causing marine invertebrates in Cambrian seas like corals and bivalves to develop hard shell tissue called ‘cellulose’.Flora And Fauna Of The Cambrian PeriodThis period witnessed major evolutionary advancements in multicellular organisms on earth. The fossils from the Cambrian period are very important for paleontologists, as they provide information about the evolution that took place over 1 billion years ago.Plant fossils did not exist during this time, and animals that were part of this environment included organisms such as liverworts, mosses, and ferns between the Cambrian rocks.These simple plants of the Cambrian system did not have a vascular structure to support their tall frames, but they did grow in moist habitats near freshwater sources or the Cambrian seas.The land was barren except for these primitive plants, which made it difficult for any other types of plant life to exist on or near the surface. As a result, creatures at this time had to adapt to survive in this environment.On land, primitive mosses grew in the soil produced by weathering rocks. Algae clung to Cambrian rocks and moisture-laden soil in freshwater.The land was barren except for simple plants such as liverworts, mosses, and the minimally vascular cryptogams (mosses, ferns, and their relatives).The mass extinction of these animals led to a boom in other extant phyla, which took advantage of the new ecological niches in their new life forms.As far as life forms and Cambrian animals are concerned, many great developments happened during the Cambrian period, like the appearance of hard shells in invertebrates.The Cambrian period was preceded by Precambrian time, which lasted for billions of years.During this epoch, many complex organisms like algae and fungi came into existence, but they did not leave any fossils for us.As far as the Cambrian period is concerned, it started with the rapid diversification of marine invertebrates in Lower Cambrian (Atdabanian) time, which then led to an increase in the number of shelled invertebrates during the middle Cambrian or mid Cambrian (Botomian).Many different types of invertebrate animals, or animals with shells, made their first appearance, or evolved, accordingly in the Cambrian period.For example, in the Cambrian period, we have Anomalocaris, who evolved from arthropods that were present during Precambrian time.This period also witnessed the evolution of many brachiopods and trilobites that became part of marine life after they evolved from primitive little life forms, like sponges etc.The fauna of the Cambrian period is divided into three series: Pikaia gracilens - the earliest known species of pikaia was discovered by Charles Walcott at Burgess Shale (British Columbia).It was about 0.47 in (12 mm) in length and looked like a worm. However, recent findings suggest that it might be an ancestor for all other vertebrates living on earth today.The opabinia regalis, a Cambrian animal, was found in Canada and had five eyes, a long claw-bearing arm, and long whip-like tentacles.Nectocaris pteryx: the first specimen of this species was discovered by Charles Doolittle Walcott at Burgess Shale (British Columbia) in 1910.It belongs to a family called cephalopod mollusks, which includes the octopus and squid.The ancient sea scorpion creature inhabited the shallow marine environment during the early Cambrian period. It is believed that scorpion-like creatures evolved from lobopodians (small, soft-bodied worm-like animals).Anomalocaris canadensis was described by Charles Walcott as’ opabinia regalis’. It is believed that the Anomalocaris was a predator who preyed on trilobites.Cambrian Period FoodThere were very few organisms living during the Cambrian period, so there wasn’t much food available. However, most of them survived by feeding on trilobites and other sea creatures.Trilobites were common invertebrate marine organisms that appeared in huge numbers around present-day Canada and Greenland.The first known complex terrestrial life forms (arthropods) existed at the end of the Cambrian period.These early arthropods are said to have resembled spiders with multiple limbs growing from their segmented bodies, like the one found inside an ancient volcanic crater today as part of Petrified Forest National Park (Arizona).The arthropleura was a giant millipede – up to 8.5 ft (2.6 m) long, with pairs of legs that could be 15 times as long as its body, which enabled it to move rapidly while foraging the land for insects and other small animals.It existed approximately 350 to 280 million years ago during the Carboniferous period.The first fish appeared around 460 million years ago, just before or at the beginning of the Ordovician period.The Cambrian ExplosionThe Cambrian Explosion, or Cambrian Radiation, is considered to be a unique and rapid event in evolutionary history, since most major animal phyla appeared within a short window of geological time.The event was labelled ’the Cambrian Explosion’ by American paleontologist, Charles Walcott, who worked with British paleontologists Edwin Colbert and Robert Trilobite in the 1950s.The Cambrian Explosion was an event in the history of life on Earth where most major groups (phyla) of complex animals appeared in the fossil record. It also led to mass extinctions.The Cambrian Explosion marked the final separation between animal phyla and plants, fungi, protoctista, and algae, and it laid the groundwork for evolutionary progress that continues to this day.The Cambrian Explosion is likely linked to an increase in the oxygen concentration of the Earth’s atmosphere, which may have allowed for the diversification of biological life forms.The Cambrian Explosion is no longer a geological time period, but an evolutionary event marking the beginning of all new groups of animals with hard shells preserved as fossils.Before the Cambrian period, life on Earth consisted of one-celled organisms and other less complex structures.But the appearance of a new group, so rich and diversified as the arthropods, or even a much older group like brachiopods, challenged evolutionary biologists to come up with a credible explanation for the explosiveness of this period in living organisms.
The name ‘Cambrian Explosion’ refers to a period in Earth’s history where an unusually large number of new lifeforms developed over a relatively short amount of time.
