Cambrian facts for kids
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The Cambrian Period (pronounced KAM-bree-ən or KAYM-bree-ən) was a super ancient time in Earth's history, lasting from about 538.8 million years ago, right after the Ediacaran Period, until about 486.85 million years ago, when the Ordovician Period began. It's famous for a huge burst of new life called the "Cambrian Explosion," when many different kinds of animals, especially those with hard shells, suddenly appeared in the oceans. During this time, the continents were mostly grouped together in the Southern Hemisphere, and the climate was generally warm.
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Where Did the Name "Cambrian" Come From?
The name "Cambrian" comes from "Cambria," which was the ancient Roman name for Wales, a country in the United Kingdom. This is because the rocks from this time period were first studied there by a brilliant scientist named Adam Sedgwick in 1831. He was exploring the mountains of North Wales and noticed unique layers of rock that told a story of a very ancient time.
Earth's Changing Face
During the Cambrian Period, the continents weren't where they are today.
Key Continents and Oceans:
- Gondwana: This was a massive supercontinent, much larger than any other landmass at the time. It stretched from the South Pole all the way up past the equator.
- Laurentia: This continent, which would eventually become North America, sat right across the equator.
- Iapetus Ocean: This ocean separated Laurentia from Gondwana, slowly opening up as the continents drifted apart.
- Baltica: This landmass, which would become parts of Europe, was located between Laurentia and Gondwana.
- Siberia: This continent, now part of Asia, was also located in the Southern Hemisphere, close to Gondwana.
Scientists use clues from Earth's ancient magnetism, where ancient animals lived, how continents moved, and what the climate was like to reconstruct these ancient maps. It's like being a detective, piecing together evidence from millions of years ago!
The Cambrian Explosion: A Burst of Life!
The most exciting thing about the Cambrian Period is something called the Cambrian Explosion. Before this time, most living things were tiny, single-celled organisms or simple, soft-bodied creatures that didn't leave many fossils. But during the Cambrian, something amazing happened: life on Earth suddenly became much more complex and diverse!
Many of the basic body plans for animals we see today first appeared during the Cambrian. This includes the ancestors of arthropods (like insects and crabs), molluscs (like snails and squids), and even early vertebrates (animals with backbones, like us!).
A big change was the development of hard shells, skeletons, and other tough body parts. These made it much easier for animals to be preserved as fossils, which is why we find so many amazing Cambrian fossils!
Animals started to burrow into the seafloor, mixing up the mud and sediments. This changed the ocean floor forever, creating new homes and food sources for other creatures. Before this, the seafloor was mostly covered by flat mats of microbes.
Trilobites are super famous Cambrian fossils. They had tough shells reinforced by calcium carbonate, which fossilized easily. This is why we find so many of their remains. The Cambrian Period is famous for special places called "Lagerstätten" (pronounced LAH-ger-shtaht-ten). These are sites where fossils are incredibly well-preserved, even showing the soft parts of animals that usually decay and disappear. It's like finding a perfectly preserved ancient photograph! Famous examples include the Burgess Shale in Canada and the Maotianshan Shales in China.
Earth's Climate During the Cambrian
The Cambrian Period was generally a time of greenhouse climate conditions. This means it was quite warm, with no large ice caps at the poles.
Scientists estimate that global average temperatures were around 20–25 °C (68–77 °F), which is warmer than today's average. Tropical sea surface temperatures could have been even hotter, around 28–38 °C (82–100 °F). The warm climate was linked to higher levels of carbon dioxide (CO2) in the atmosphere, which acts like a blanket, trapping heat.
Atmospheric oxygen levels were lower than today, ranging from about 3% to 14% (compared to about 21% today). This meant that deep ocean waters often had very little or no oxygen, a condition called anoxia.
These changing oxygen levels and warm temperatures created a dynamic environment. Sometimes, low-oxygen waters would rise to the surface, causing extinction events, but then new life would evolve to fill those spaces, leading to even more biodiversity!
Geological Timekeeping
Scientists divide the Cambrian Period into smaller chunks of time, like chapters in a book. These are called series (or epochs) and stages. To mark the beginning of each new chapter, they choose a special, officially chosen spot in the world called a Global Boundary Stratotype Section and Point (GSSP). It's like a scientific landmark!
Cambrian Chapters:
- Terreneuvian Series (538.8 to ~521 Ma): This is the earliest part of the Cambrian. Its base is marked by the first appearance of a special trace fossil called Treptichnus pedum (a type of burrow) at Fortune Head in Newfoundland, Canada. No trilobites here yet!
- Cambrian Series 2 (~521 to ~506.5 Ma): This part saw a rapid increase in different kinds of animals, including the first trilobites. Scientists are still working to find the perfect GSSP for its base.
- Miaolingian Series (~506.5 to ~497 Ma): Named after the Miaoling Mountains in China, this series is marked by the first appearance of a specific trilobite called Oryctocephalus indicus.
- Furongian Series (~497 to 486.85 Ma): This is the latest part of the Cambrian, named after the Wuling Mountains in China. Its base is marked by the first appearance of another trilobite, Glyptagnostus reticulatus.
The end of the Cambrian and the start of the Ordovician Period is marked at Green Point, Newfoundland, Canada, by the first appearance of a tiny, eel-like creature with special teeth called Iapetognathus fluctivagus.
Earth's Scars
Even during the Cambrian, Earth was sometimes hit by space rocks! Scientists have found evidence of several large meteorite impact craters from this period:
- Neugrund crater (Estonia): About 20 km (12 miles) wide, formed around 535 million years ago.
- Gardnos crater (Norway): About 5 km (3 miles) wide, formed around 500 million years ago.
- Glikson crater (Western Australia): About 19 km (12 miles) wide, formed around 508 million years ago.
These impacts would have caused huge changes to the local environment, but thankfully, life in the oceans was vast enough to recover.
Ancient Chemistry: Geochemistry
Scientists also study the chemistry of ancient rocks to understand the Cambrian. They look at isotope ratios, which are like chemical fingerprints that tell us about changes in the oceans and atmosphere.
- Carbon Isotopes (δ13C): Big changes in carbon isotopes tell us about how much carbon was being buried in the ocean floor, which affects oxygen levels and climate.
- Strontium Isotopes (87Sr/86Sr): These tell us about how much continents were eroding and washing nutrients into the oceans.
- Magnesium/Calcium Ratios: The amount of magnesium and calcium in seawater changed, which affected how animals built their shells and skeletons. Sometimes the oceans were "aragonite seas" (where aragonite was the main type of calcium carbonate), and sometimes they were "calcite seas" (where calcite was dominant).
These chemical changes were closely linked to the evolution of life, sometimes causing extinctions and other times helping new species to thrive.
Plant Life in the Cambrian
The Cambrian Period was mostly about marine life. On land, there weren't any big plants like trees or flowers yet. The main "flora" (plant life) was marine macroalgae (like ancient seaweeds) in the oceans. On land, there were probably simple microbial mats and biofilms, like slimy crusts, but no true land plants had evolved yet. The first clear evidence of land plants comes from the period after the Cambrian, the Ordovician.
The End of the Cambrian
While the early Cambrian was a time of incredible diversification, the later half of the period saw several extinction events. For example, around 500 million years ago, oxygen levels in the oceans fell dramatically, and poisonous hydrogen sulfide increased, causing many species to die out. The amazing Archaeocyatha, which built the first reefs, went extinct, and the older stromatolites (dome-shaped structures built by tiny microbes) made a comeback. This declining trend didn't change until the Great Ordovician Biodiversification Event, which happened in the next period.
Images for kids
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Archeocyathids from the Poleta formation in the Death Valley area
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A reconstruction of Margaretia dorus from the Burgess Shale. They were once thought to be green algae, but are now known to be related to hemichordates.
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Stromatolites of the Pika Formation (Middle Cambrian) near Helen Lake, Banff National Park, Canada
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Trilobites were very common during this time.
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Anomalocaris was an early ocean predator, one of the many arthropods of the time.
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Opabinia was a creature with an unusual body plan; it was probably related to arthropods.
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Protichnites were the tracks left by arthropods walking on Cambrian beaches.
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Hallucigenia sparsa was a member of the lobopodian group, related to modern velvet worms.
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Cambroraster falcatus was a large arthropod for that era.
See also
In Spanish: Cámbrico para niños
