Cambrian

The Cambrian is the first geological period of the Paleozoic Era and the Phanerozoic Eon. It lasted about 52 million years, from 539 million years ago to 487 million years ago.

During this time, most of the continents were in the southern half of the Earth, surrounded by a huge ocean called the Panthalassa Ocean. One of these continents, Gondwana, began to form and changed the Earth's climate and landscapes.

The Cambrian is very important for life on our planet. Before this time, most living things were very simple, single-celled organisms. But during the Cambrian, something amazing happened called the Cambrian explosion. Many new, more complex animals with different body plans appeared quickly. This was the first time we see representatives of most major animal groups that exist today. The Cambrian also has many special fossil sites, called lagerstätte, where scientists can find extremely well-preserved remains of ancient animals.

Etymology and history

The word Cambrian comes from the Latin name for Wales, Cambria. Scientists first studied rocks from this time there. A scientist named Adam Sedgwick created the name in 1831 after his work in North Wales. He split the Cambrian into three parts: Lower, Middle, and Upper.

Sedgwick and another scientist, Roderick Murchison, worked together to decide the end of the Cambrian period. But they disagreed about where the boundary should be. In 1879, a scientist named Charles Lapworth solved the problem by naming the disputed rocks the Ordovician period. The name Cambrian was officially accepted in 1960.

Geology

Systems, series and stages can be defined globally or locally. The ICS choose rock units based on a Global Boundary Stratotype Section and Point (GSSP) from one formation (a stratotype). This marks the start of each unit. The Cambrian System has boundaries set by these special points.

The bottom of the Cambrian was once thought to mark the first complex life, shown by trilobites. But we now know of small shelly fossils before trilobites, and Ediacara biota even earlier. This has led some to want a more exact start for the Cambrian Period.

The Terreneuvian is the first part of the Cambrian, from 538.8 ± 0.6 million years ago to about 521 million years ago. It has two parts: the Fortunian stage, from 538.8 ± 0.6 million years ago to about 529 million years ago; and an unnamed stage from about 529 million to 521 million years ago. The name Terreneuvian was officially chosen by the International Union of Geological Sciences (IUGS) in 2007. The Terreneuvian is the only part of the Cambrian without trilobite fossils.

The Miaolingian is the third part of the Cambrian, from about 506.5 million years ago to about 497 million years ago. It has three parts: the Wuliuan from about 506.5 million to 504.5 million years ago; the Drumian from about 504.5 million to 500.5 million years ago; and the Guzhangian from about 500.5 million to 497 million years ago.

The Furongian, from about 497 million years ago to 486.85 ± 1.5 million years ago, is the last part of the Cambrian. It has three parts: the Paibian, from about 497 million to 494 million years ago; the Jiangshanian from about 494.2 million to 491 million years ago; and an unnamed stage from about 491 million to 486.85 ± 1.5 million years ago.

Some big meteorite impacts happened during the early Cambrian: the Neugrund crater in the Gulf of Finland, Estonia; the Gardnos crater in Buskerud, Norway; the Presqu'ile crater in Quebec, Canada; the Glikson crater in Western Australia; the Mizarai crater in Lithuania; and the Newporte structure in North Dakota, U.S.A.

Paleogeography

During the Cambrian period, scientists studied rocks and fossils to learn where continents were. This helps us understand how Earth looked long ago, but there is still some debate about the exact positions.

Most models show a large landmass called Gondwana stretching from near the South Pole towards the equator. Another large landmass, Laurentia, sat near the equator, separated from Gondwana by a wide ocean called the Iapetus Ocean. Smaller continents such as Baltica, Siberia, and parts of China moved in different directions, shaping the early oceans and seas of our planet.

Climate

The Cambrian period had a warm climate with lots of carbon dioxide in the air. The whole planet was warm, from the poles to the equator. Scientists think average temperatures were about 20–25 °C (68–77 °F), much warmer than today.

The oceans were warm too, and there was less oxygen in the air, about 3% to 14% of what we have now. These warm, low-oxygen conditions affected the animals that lived in the seas and helped shape life on Earth long ago.

Geochemistry

During the Cambrian, the chemistry of the oceans and atmosphere changed often. These changes can be seen in the ratios of different elements found in rocks. The changes happened because of many factors, including volcanic activity, weather patterns, and the actions of early sea creatures.

At the start of the Cambrian, there was a big change in carbon ratios. This showed that there was low oxygen in shallow seas. This was when many new animal groups began to appear. Later in the Cambrian, more changes happened as mountains wore down and volcanoes erupted. These events affected the oceans and the creatures living there. The changes led to more oxygen in some places and less in others, which influenced which animals could survive and thrive. The chemistry of the seas also affected the kinds of shells and skeletons that animals could build.

Flora

The Cambrian period had simple plants, mostly in the ocean. Important sea plants included Fuxianospira, Sinocylindra, and Marpolia. There were no plants on land during this time.

Scientists think land plants might have started to appear late in the Cambrian, but the first clear evidence of land plants came later, in the Ordovician period. Microbes formed mats on beaches and helped shape early soils.

Oceanic life

The Cambrian explosion was a time when many new animals quickly appeared and grew. Most of these animals lived in the ocean. Trilobites were very common because of their strong, rocky shells, but they were just a small part of all the ocean animals. Other animals with softer bodies were more common but harder to find as fossils.

During this time, the variety of life in the sea changed a lot. Many older sea creatures disappeared, and new types of animals began to dig into the ocean floor. This digging changed the sea floor forever. Even though life was growing at first, later in the Cambrian period, the number of animal species went down because of changes in the ocean’s oxygen and chemical levels. Some sea life even began to move onto land, leaving behind tracks in the mud.

Symbol

The United States Federal Geographic Data Committee uses a special symbol to show the Cambrian Period. This symbol is a "barred capital C" ⟨Ꞓ⟩. The symbol is part of Unicode. Unicode is a system that includes characters from writing systems around the world. The code for this symbol is U+A792 Ꞓ LATIN CAPITAL LETTER C WITH BAR.