Cambrian

The Cambrian is the first geological period of the Paleozoic Era and the Phanerozoic Eon. It lasted about 52 million years, from 538.8 million years ago to 486.85 million years ago. During this time, Earth changed a lot for living things.

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 an exciting time for life on Earth. 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 very 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 52 million years, from 539 million years ago to 487 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 learn 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

We learn about where continents were during the Cambrian period from old magnetic records, rocks, and Earth's movements. Most continents were in the southern part of Earth, surrounded by a big ocean called Panthalassa. But scientists are not sure exactly how these landmasses were arranged.

One big continent, Gondwana, stretched from near the South Pole to areas north of the equator. Another continent, Laurentia, sat near the equator. It was separated from Gondwana by the Iapetus Ocean. Smaller lands such as Baltica, Siberia, and parts of what would become China and Australia were in different places around these bigger continents. These lands moved slowly over time because of Earth's shifting plates.

Climate

The Cambrian period had warm weather, like a greenhouse. There was a lot of carbon dioxide in the air. This warmth changed the oceans, making deeper waters have less oxygen.

Life changed fast during this time because sometimes there was more oxygen. These changes in oxygen helped create many new kinds of life.

Geochemistry

During the Cambrian, the chemistry of the oceans and atmosphere changed a lot. Scientists study things called isotope ratios to learn about these changes. These ratios helped them understand how the Earth’s surface and life interacted long ago.

At the start of the Cambrian, there was not much oxygen in shallow ocean waters. This was when many early animal groups began to appear and grow in number. Later, volcanic activity released gases that changed the climate and ocean chemistry. These changes made sea levels 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, plants in the oceans looked similar to those from earlier times. The main plants were large sea algae named 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 sandy areas of old beaches and tidal flats around 500 million years ago. These tiny living things helped create soil, much like what we see in dry desert areas today. Some scientists think that land plants might have begun 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 appeared in the time period that came after, called the Ordovician.

Oceanic life

The Cambrian explosion was a time when many new sea creatures appeared very 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 disappeared, 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⟩, for the Cambrian Period. This symbol is part of the Unicode standard and has the code U+A792 Ꞓ LATIN CAPITAL LETTER C WITH BAR.