The Cambrian Period is the first period of the Paleozoic Era, marking the beginning of the Phanerozoic Eon.
The period lasted about 55 million years between 541 million and 485.4 million years ago.
It is named after “Cambrian,” the Latin name for Wales, where rocks corresponding to that period were first identified in Britain.
Adam Sedgwick, one of the pioneers of the study of geology, assigned the name to the period in 1835.
The Cambrian Period was a time of dramatic change in the Earth’s evolutionary history.
The period is characterized by the rapid appearance of varied life forms.
Within just 13 million years, many of the major animal groups alive today (and several other extinct groups) evolved.
This period, known as the Cambrian explosion or the biological big bang, is one of the most significant events in the history of life on Earth.
The Cambrian Period is also known for the appearance of organisms with mineralized (hence readily fossilized) body parts.
This made it possible for scientists to keep clear fossil records to track the evolution of life on Earth.
In addition to the changes in life forms, the Earth’s climate and geography also changed significantly during the Cambrian.
In this post, we’ll discuss the timeline of the Cambrian Period and trace the changes that took place in terms of the climate, geography, and key events that occurred during the period.
Timeline of the Cambrian Period
The Cambrian Period is the first period of the last 542 million years of Earth’s geologic history — the Phanerozoic Eon.
It is also the first of the six subdivisions of the Paleozoic Era (541Ma – 251Ma). The period encompassed a duration of approximately 55 million years (541–485.4 Ma).
The Cambrian Period started at the end of the Ediacaran Period (the last period of the Proterozoic Eon).
It lasted till the beginning of the Ordovician Period, about 485.4 million years ago.
The entire period is further divided into four epochs or subperiods, namely:
- Terreneuvian Series, which lasted from 541 to 521 million years ago
- Cambrian Series 2, which lasted from 521 to 509 million years ago
- Cambrian Series 3 (or Miaolingian), which lasted from 509 to 497 million years ago
- Furongian Series, which started 497 million years ago and lasted till 485.4 million years ago
Terreneuvian Series (541–521 Million Years Ago)
The Terreneuvian Series is the first subdivision of the Cambrian Period.
During this time, the Earth’s climate was starting to warm up after an extended period of widespread glaciation and extremely cold temperatures.
There was no life on land throughout this subperiod and for the rest of the Cambrian.
Instead, most of the planet was covered by water. The sea level was quite high at the beginning of the Cambrian due to melting glaciers.
It is worth noting that life did exist in Earth’s oceans before the Cambrian Period.
But the majority of organisms that were alive during the Late Proterozoic Eon and Early Cambrian Period were small, unicellular forms.
They lived on the seafloor covered in oxygen-free and sulfide-rich microbial mats.
About 538.8 million years ago, more complex animal forms began to emerge.
The Early Cambrian marine ecosystems also began to diversify, with the emergence of animals with different body plans that expanded into new ecological niches.
The Terreneuvian is characterized by the appearance of the earliest living organisms with hard shells, including the first trilobites, brachiopods, and other small shelly fossils.
During this period, the supercontinent was just starting to break up, and the continents were arranged differently from their current forms.
Cambrian Series 2 (521–509 Million Years Ago)
The planet continued to warm up during the second subdivision of the Cambrian Period.
Sea levels also continued to rise, leading to widespread flooding of continental margins.
By this time, the continents were arranged into two landmasses: Gondwana and Laurentia.
These massive landmasses were surrounded by a global ocean known as the Panthalassic Ocean.
The Cambrian Series 2 was characterized by further diversification of marine life, which occurred rapidly.
Arthropods (especially trilobites) were the most abundant organisms in the Cambrian seas, and they continued to evolve into new forms.
Mollusks, including snails and clams, made their first appearance around this period.
The rise of burrowing organisms around this time indicates the growing ecological complexity of the Cambrian life forms.
Their activities also helped transform the sea floor, creating even more complex ecosystems.
Gondwana (which included the landmass of present-day Australia, Antarctica, India, Africa, and South America) remained intact during this period, but it was drifting away from its initial position.
Laurentia was also moving northward towards the equator.
Cambrian Series 3 (Miaolingian) (509–497 Million Years Ago):
The climate remained warm and stable during this epoch.
The sea level was also high, favoring the formation of shallow marine environments where new aquatic lifeforms could evolve further.
The most notable event of the Cambrian Series 3 was the appearance of the first chordates, considered the early ancestors of the vertebrates.
This period is also characterized by the development of the first true predators of the marine ecosystem.
This triggered an evolutionary arms race with prey organisms, developing various defensive mechanisms to survive.
The predator-prey relationship increased the complexity of the ecosystem further as new species evolved and interacted.
The continents continued to drift forward, and the two large landmasses started to break apart as well, forming several continents.
By the end of the Cambrian Series 3, the landmass of Laurentia and Baltica were positioned close to the equator.
Furongian Series (497–485.4 Million Years Ago)
The climate at the end of the Cambrian Period remained warm and stable, with only minor fluctuations.
Sea levels remained high, and this facilitated the development of coral reefs built by colonial organisms called archaeocyathids.
The Furongian Series is considered the peak of the diversification of marine life that took place during the Cambrian.
Arthropods, including trilobites and arachnids, remained the most abundant organisms. They underwent significant radiation and exhibited a wide array of body forms.
Near the end of this series, the first jawed fish appeared.
This represents an important milestone in vertebrate evolution.
However, life at the end of the Cambrian was generally less diverse compared to the early half of the period.
The Ordovician Period, which follows the Cambrian, ended with an extinction event that wiped out many of the Cambrian species.
Experts believe some Cambrian organisms may have ventured onto land towards the end of the period.
Evidence for this includes trace fossils known as Protichnites and Climactichnites.
These trace fossils have been interpreted as evidence that an extinct group of arthropods may have walked on land.
Climate and Geography of the Cambrian Period
During the Proterozoic Eon, the Earth’s climate was generally cold.
However, a warming trend began just shortly before the Eon ended and the Cambrian Period began.
The supercontinent Rodinia also began to break up shortly before the Cambrian Period began.
By the Early Cambrian Period, there were two main continents, and a smaller one formed from Rodinia.
The landmass of Gondwana was closer to the South Pole.
It included the continental landmass that would later form present-day Africa, Australia, South America, Antarctica, and parts of Asia.
The second major landmass was Laurentia, which comprised the landmass of present-day North America and some parts of Europe.
A third but smaller landmass, Baltica (made up of present-day western Europe and Scandinavia), also existed close to Laurentia.
Baltica was starting to drift northward from Laurentia at the start of the Cambrian.
Throughout the Cambrian Period, the continents continued drifting apart, with Gondwana shifting towards the South Pole while Laurentia and Baltica were moving closer to the equator.
These movements set the stage for future configurations of the continents.
The Earth’s climate was temperate and stable during the Middle Cambrian and generally grew warmer towards the end of the period.
Melting ice as the planet warmed up led to a rise in sea levels and extensive flooding of continental margins.
The Late Cambrian climate is comparable to the climate of the Late Cretaceous and Early Palaeogene periods.
The transition from a global ice age to a warmer and more stable climate created favorable conditions for the diversification of marine life during the Cambrian.
Key Events and Developments of the Cambrian Period
The Cambrian Period was characterized by several key events starting from the Cambrian explosion and the establishment of complex marine ecosystems that followed it.
In addition to the emergence of several new groups of organisms, some other notable developments took place that contributed to the complexity of Earth’s newly evolving ecosystems of the Cambrian.
Also known as the “Biological Big Bang,” it was a period of rapid diversification of living organisms in the Cambrian Ocean.
It is referred to as an explosion because the diversification took place over a short period of about 13–25 million years, starting from about 538.8 million years ago.
The period is characterized by a significant increase in the number and variety of major animal phyla.
Before the Cambrian, life primarily consisted of simple, single-celled organisms.
The explosion introduced a multitude of organisms with new body plans, morphologies, and ecological strategies.
This set the stage for the subsequent evolution of life on Earth.
Evolution of Hard Body Parts
The Cambrian Period is not only known for the rapid diversification of organisms, but it also witnessed the evolution of the first organisms with hard body parts.
The Cambrian organisms evolved exoskeletons mainly for increased protection, support, and predation capabilities.
However, these mineralized shells, spines, and other exoskeletons have played an important role in our understanding of animal evolution.
This is because they were more easily preserved as fossils compared to the soft body parts of their ancestors.
The Emergence of Burrowing Organisms
During the Cambrian’s early years, burrowing organisms capable of tunneling through sediments evolved.
The seafloor of Precambrian Earth was covered by a microbial mat that sustained the simple cellular organisms that were alive at the time.
The burrowers reshaped the seafloor and created new ecological opportunities, allowing new organisms to evolve.
The burrows provided access to buried food resources and contributed to the oxygenation of sediment layers, influencing sedimentary processes and the complexity of marine ecosystems.
Formation of Coral Reefs
During the later stages of the Cambrian Period, primitive reef-building organisms called archaeocyathids appeared.
These organisms secreted calcium carbonate structures that formed reef-like structures in the water.
Although different from modern coral reefs, these structures created habitats for other organisms, provided protection, and influenced local sedimentation patterns.
The development of these early reefs foreshadowed the future evolution of complex reef ecosystems that still exist today.
Major Groups of Organisms in the Cambrian Period
The Cambrian Period is characterized by the appearance of most of the animal phyla that we know today.
In fact, the only animal phylum that evolved after the Cambrian is the Bryozoa.
The following are the major groups that were most abundant during this period:
As it is today, arthropods were the largest and most diverse group of animals on Earth back in the Cambrian.
The group experienced significant radiation in the Early and Middle Cambrian.
This Arthropoda phylum includes living groups like insects, spiders, crustaceans, as well as extinct groups like the trilobites.
They occupied a wide range of ecological niches and played diverse roles in the marine ecosystems of the Cambrian.
Brachiopods were abundant and diverse during the Cambrian Period and have persisted throughout much of Earth’s history.
The brachiopods of the Cambrian were sessile filter feeders.
They used a specialized structure called a lophophore to capture suspended food particles in the water.
The mollusk group includes organisms such as snails, clams, and cephalopods.
Mollusks possess a soft body typically covered by a hard shell.
They exhibit a wide range of feeding strategies and ecological roles, including herbivory, predation, and filter feeding.
The echinoderms of the Cambrian are ancestors of modern starfishes, sea urchins, and sea lilies, which emerged and diversified during the Cambrian Period.
Members of this group are known for their unique five-fold radial symmetry.
Echinoderms were predators, grazers, and filter feeders in the Cambrian ecosystem.
Chordates are a group of animals that include modern vertebrates and their closest relatives.
The earliest chordates that appeared during the Cambrian were small and simple.
They looked nothing like the living members of the group. The defining feature of these early chordates was a notochord, a type of primitive spinal structure.
Scientists consider the Cambrian chordates to be the earliest ancestors of modern vertebrates.
Notable Species from the Cambrian Period
Some of the most notable animal species that have been identified from the Cambrian Period are listed below:
Trilobites were one of the most successful and diverse groups of arthropods during the Cambrian.
In fact, they were so abundant that trilobite species are used as markers for different stages of the Cambrian.
They possessed a hard exoskeleton divided into three lobes, hence their name.
Trilobites exhibited a wide range of body shapes, sizes, and ecological adaptations, and they occupied various marine habitats.
Antarcticocyathus was a type of reef-building marine organism closely related to modern sponges.
They lived in the warm tropical and subtropical seas of the Early and Middle Cambrian periods.
This was a shrimp-like arthropod that’s often regarded as one of the most fearsome predators of the Cambrian Period.
Anomalocaris had fearsome mouthparts lined with hooks that it used to trap prey.
Opabinia was a soft-bodied basal arthropod that lived on the Cambrian seafloor.
It had a striking appearance which included five eyes, backward-facing eyes under its body, and a clawed proboscis, which it used for feeding.
Wiwaxia was a small marine organism whose exact classification and relationship with other organisms is still being debated.
It was covered in shell or armor-like plates and had rows of spines all over its flattened body.
The Wiwaxia is considered a key species in understanding the early evolution of animals.
Fossils and their Significance in Understanding the Cambrian Period
The Cambrian Period represents a critical interval in the fossil record for two main reasons.
The first is the change in marine conditions that favored exceptional fossil preservation.
Locations such as the Burgess Shale and Chengjiang Biota have been noted for their remarkable preservation of soft-bodied organisms that were typically rare in the fossil record before the Cambrian Period.
The Cambrian Period also saw the evolution of animal groups with mineralized hard parts.
These hard parts had a higher chance of being preserved and fossilized than the soft tissues of organisms that lived before this period.
As a result, the fossil record of the Cambrian Period is rich in well-preserved fossils with mineralized structures.
Trilobites are among the most recognizable and abundant fossils from the Cambrian Period.
They had tough exoskeletons that are often well-preserved in the fossil record.
This remarkable preservation has provided scientists with valuable information about their morphology, ecology, and the diversity of Cambrian organisms.
Trilobite species and other well-represented organisms of the Cambrian serve as excellent index fossils, aiding in the relative dating of Cambrian rocks and the correlation of different fossil assemblages.
The Cambrian Explosion and its Impact on Evolution
The Cambrian explosion was a relatively short burst of evolutionary diversification characterized by the emergence of many major animal groups.
This event is often referred to as the biological big bang because of its profound impact on the subsequent evolution of life on Earth.
The Cambrian explosion represents the fastest growth in the number of major new animal groups in Earth’s history.
During this period, organisms with various body plans, anatomical features, and ecological strategies emerged.
This explosion of diversity laid the foundation for the subsequent evolutionary trajectory of life on Earth.
In contrast to the animals of the previous era, the Cambrian explosion is marked by the appearance of organisms with complex body parts such as distinct heads, tails, limbs, and sensory organs.
This marked a major transition from simpler forms of life and set the stage for the evolution of more advanced and specialized organisms in later periods.
Another notable aspect of evolution during the Cambrian explosion was the evolutionary arms race.
With the development of predation, animals began to evolve specialized feeding structures and behaviors that led to new ecological interactions and shaped the structure of marine ecosystems.
Complex food webs were established, and many prey species evolved defense mechanisms to stand a chance against predators.
The Cambrian explosion no doubt left a significant imprint in the fossil record.
As many new and diverse organisms appeared, they were rapidly fossilized.
The exceptional preservation of the animals that evolved during this period has provided invaluable insights for scientists studying the anatomy, diversity, and ecological relationships of Cambrian organisms.
Extinction Events and Their Effects on the Cambrian Period
Although the Cambrian Period is known for its remarkable evolutionary explosion, there were also a few localized extinction events that impacted the trajectory of life during that time.
These extinction events were not on the scale of the ones that occurred in later periods but were still significant enough to influence the dynamics of the Cambrian ecosystems.
Some of these events include:
The End-Botomian extinction event occurred at the boundary between the Terreneuvian and Cambrian Series 2 epochs approximately 521 million years ago.
This event was relatively localized and primarily affected shallow marine environments.
It resulted in the disappearance of certain groups of organisms, including some early trilobite species.
However, it did not disrupt the overall trajectory of Cambrian evolution.
The Toyonian event, also known as the “Great Unconformity,” occurred around the boundary between the Cambrian Series 2 and Cambrian Series 3 epochs approximately 509 million years ago.
This event was marked by a significant decrease in sedimentation rates and the erosion of existing rock layers.
While not an extinction event in the traditional sense, it disrupted the preservation of fossil records and resulted in a gap in the geological record.
Late Cambrian Extinction
Towards the end of the Cambrian Period, around 497 million years ago, the Late Cambrian extinction event took place.
This event primarily affected trilobites and conodonts, leading to the decline and extinction of many species within these groups.
It resulted in a turnover of trilobite fauna and paved the way for the subsequent rise of other groups in the Ordovician Period.