Cambrian

The Cambrian is the first geological period of the Paleozoic Era and the Phanerozoic Eon. It lasted 51.95 million years, from 538.8 million years ago to 486.85 million years ago. During this time, Earth saw many important changes in the living world.

Most continents were in the southern half of the planet, surrounded by a huge ocean called the Panthalassa Ocean. A large landmass called Gondwana was forming, and another called Laurentia sat near the equator, separated from Gondwana by the Iapetus Ocean.

The Cambrian was a special time for life on our planet. Before this period, most living things were very small and simple. But during the Cambrian, many new kinds of animals appeared quickly. This burst of new life is called the Cambrian explosion. It brought the first members of most animal groups we know today. The Cambrian also had many places where fossils were preserved extremely well, showing even soft parts of ancient creatures.

Etymology and history

The word Cambrian comes from the Latin name for Wales, called Cambria by the ancient Romans. Scientists first studied rocks from this time in Wales. A scientist named Adam Sedgwick gave the Cambrian its name in 1831 after studying these rocks in North Wales. He worked with another scientist, Roderick Murchison, to help set the limits of the Cambrian time period.

Later, there was some disagreement about exactly where the Cambrian ended and another period, the Silurian, began. This disagreement lasted many years until another scientist, Charles Lapworth, suggested creating a new period called the Ordovician to fit the rocks in question. The name Cambrian was finally agreed upon in 1960 by scientists from around the world.

Geology

The Cambrian was the first long period of time in a big part of Earth's history called the Paleozoic Era. It lasted for about 51.95 million years, from 538.8 million years ago to 486.85 million years ago. During this time, most of the Earth's land was in the southern half of the planet, with a huge ocean called Panthalassa surrounding it.

Scientists study rocks from this time to understand how life changed. They use special points in the rocks, called Global Boundary Stratotype Section and Points (GSSPs), to mark the start and end of different parts of the Cambrian. These points help them compare rocks from different places around the world. The Cambrian is split into four main parts, or series, each with its own stages. The first part, called the Terreneuvian, started with the first signs of complex life. Later parts saw more kinds of life appearing and changing quickly.

Paleogeography

The positions of continents during the Cambrian period are understood using information from ancient magnetic records, rock formations, and geological activity. While scientists agree that most continents were in the southern half of the Earth, surrounded by a large ocean called Panthalassa, the exact arrangement and movement of these landmasses can vary between different models.

One major continent, Gondwana, stretched from near the South Pole to regions north of the equator. Another continent, Laurentia, sat near the equator and was separated from Gondwana by the Iapetus Ocean. Smaller landmasses such as Baltica, Siberia, and parts of what would become China and Australia were positioned in various locations around these larger continents. These landmasses moved slowly over time due to the shifting of Earth's tectonic plates.

Climate

The Cambrian period had warm, greenhouse-like conditions with high levels of carbon dioxide in the air. This warmth affected the oceans, which often had low oxygen levels in deeper waters.

Life during this time evolved quickly, partly because there were periods when more oxygen was available. These changes in oxygen levels helped shape the variety of life forms that appeared.

Geochemistry

During the Cambrian, there were many changes in the chemistry of the oceans and atmosphere. Scientists study things called isotope ratios to learn about these changes. These ratios helped them understand how the Earth’s surface and life were interacting long ago.

The beginning of the Cambrian showed signs of low oxygen in shallow ocean waters. This was the same time that many early animal groups began to appear and diversify. Later in the Cambrian, volcanic activity released gases that changed the climate and ocean chemistry. These changes caused sea levels to rise, covering land areas and affecting many sea creatures. The chemistry of seawater also changed over time, influencing the types of minerals that made up the shells and skeletons of ancient sea animals.

Flora

During the Cambrian period, the plants in the oceans looked much like those from the time before. The main plants were big sea algae called Fuxianospira, Sinocylindra, and Marpolia. We do not find any stone-like sea plants from this time.

We also do not find any fossils of plants that lived on land during the Cambrian. However, there were thin layers of tiny living things on the sandy areas of old beaches and tidal flats around 500 million years ago. These tiny living things helped form soil, similar to what we see in dry desert areas today. Some scientists think that land plants might have started to appear during the Cambrian, and that some small creatures called arthropods might have moved onto land too, but the earliest clear proof of this only shows up in the time period that came after, called the Ordovician.

Oceanic life

The Cambrian explosion was a time when many new sea creatures appeared quickly. Most animals lived in the ocean, and many were arthropods, which have jointed legs and a hard shell. Trilobites, with their strong, armored shells, seemed very common because their shells fossilized well, but they were not the most numerous animals.

During this time, the variety of life in the ocean changed a lot. Many older sea creatures died out, and new ones took their place. Animals that dug into the sea floor changed the sandy bottom, which affected other sea creatures. Later in the Cambrian, the number of sea animals decreased because of changes in the ocean, like less oxygen and more poisonous gases. Some sea creatures even started to move onto land, leaving behind tracks in the sand.

Symbol

The United States Federal Geographic Data Committee uses a special symbol, a barred capital C ⟨Ꞓ⟩, to represent the Cambrian Period. This symbol is part of the Unicode standard and has the code U+A792 Ꞓ LATIN CAPITAL LETTER C WITH BAR.