Ordovician

A long time ago, the world was different.

Many animals lived in the sea.

Most of these animals had shells.

Some animals started to live on land. The first land plants grew then, too. Fish also lived in the water. Some fish may have had jaws.

Space was busy during this time. Many rocks from space hit the Earth. This happened more than it does today.

At first, the world was very hot. Later, the world got very cold. This cold time made ice grow.

This cold weather changed life in the sea. Some animals died out because of the ice. It was a very big change for our world.

The Ordovician was a long period in Earth's history.

It lasted for 43.75 million years. A man named Charles Lapworth gave it this name. He named it after the Ordovices. They were an old tribe in Wales.

Life was very busy in the oceans. Many animals lived in the sea.

Most of these animals were invertebrates. These are creatures without backbones. Molluscs and arthropods were very common.

Some fish also lived in the water. These were the first true vertebrates. A vertebrate is an animal with a backbone.

At first, the Earth was very hot. The air had a lot of carbon dioxide. Later, the world grew much colder. This led to an ice age.

This ice caused a mass extinction. Many sea animals died out during this time.

Space was also busy. Many meteorites hit the Earth. They hit 100 times more than they do today. This may have happened because of a ring around Earth. This ring likely came from a broken rock in space.

The Ordovician was a huge part of Earth's history. It was the second of six periods in the Paleozoic Era. This time lasted for 43.75 million years.

It began after the Cambrian Period ended. It finished when the Silurian Period started. This era was a time of big changes for our planet. It helped shape how life and land look today.

Life in the oceans grew very busy during this time. This is called the Great Ordovician Biodiversification Event.

Many living things like molluscs and arthropods lived in the sea. Some arthropods may have even started living on land. The very first land plants also appeared.

Fish were also evolving. They were the world's first true vertebrates, which means they had backbones. Some fish may have even grown jaws late in the period.

Scientists learned about this time through careful study. A man named Charles Lapworth defined the Ordovician in 1879.

He wanted to solve a disagreement about rocks in North Wales. Two other scientists, Adam Sedgwick and Roderick Murchison, could not agree on the rock layers. Lapworth saw that the fossils were different from other periods. He named the system after the Ordovices, a Welsh tribe. The International Geological Congress officially accepted the name in 1960.

Earth's surface was also changing in many ways. The southern continents were joined into one huge land called Gondwana.

Large oceans like the Panthalassic Ocean covered much of the world. Huge mountains formed, such as the Appalachians.

These mountains grew when island arcs collided with the continent of Laurentia. At the same time, many meteorites hit the Earth. They hit 100 times more often than they do now. This might have happened because a ring of debris circled the Earth.

Weather and sea levels changed a lot too. At first, the Earth was very hot with high carbon dioxide. Later, the world grew much colder. This led to the Hirnantian glaciation, which was a major ice age. As the world froze, sea levels fell for about 3 million years. This cold change caused the Ordovician–Silurian extinction events. Many sea creatures, like certain trilobites, died out during this hard time.

The Ordovician is a major geologic period and system. It is the second of six periods within the Paleozoic Era. It is also the second of twelve periods in the Phanerozoic Eon. This period lasted for 43.75 million years. It began when the Cambrian Period ended. It concluded when the Silurian Period started. This era was a critical time for the development of life and the shaping of Earth's geography.

Life underwent a massive transformation during this time. Scientists call this the Great Ordovician Biodiversification Event. This event significantly increased the diversity of living things. Invertebrates like molluscs and arthropods were the most common animals in the oceans. Some arthropods may have even begun to establish themselves on land. The very first land plants are also known from this period.

Fish were also evolving during this era. They were the world's first true vertebrates, which means they had backbones. Some fish might have even developed jaws late in the period.

The history of the Ordovician name is quite interesting. It was defined by Charles Lapworth in 1879. He wanted to resolve a dispute between two other scientists, Adam Sedgwick and Roderick Murchison. They could not agree on whether certain rock beds in North Wales belonged to the Cambrian or Silurian systems. Lapworth realized the fossils in these rocks were unique. He named the system after the Ordovices, a Welsh tribe that lived in that area. The International Geological Congress finally gave the period official international approval in 1960.

Earth's geography was very different during the Ordovician. The southern continents were joined into a massive landmass called Gondwana. This giant continent stretched from north of the equator all the way to the South Pole. The Panthalassic Ocean was huge and covered more than half of the entire globe.

Other continents like Laurentia, Siberia, and Baltica were separated from Gondwana by wide oceans. Small continents like Avalonia also moved, eventually colliding with Baltica toward the end of the period.

Tectonic activity was very widespread and intense. This included both volcanism and orogenesis, which is the process of mountain-building. Many mountains did not form from continent collisions. Instead, they grew along active continental margins when island arcs collided with larger landmasses. For example, the Appalachian Mountains began to form when volcanic island arcs hit Laurentia.

Other areas saw significant activity, such as the Benambran Orogeny in eastern Australia. The period also saw a massive ash fall known as the Millburg/Big Bentonite bed. This event deposited a huge volume of ash around 454 million years ago.

During the Middle Ordovician, Earth experienced a strange meteor event. About 467.5 million years ago, meteorites struck the Earth much more often than they do today. In fact, they hit about 100 times more frequently. Some scientists theorize this happened because a ring system formed around the Earth. This ring of debris may have caused frequent impacts for about 40 million years.

Interestingly, this meteor shower is not believed to be linked to any major extinction events.

Climate and sea levels shifted dramatically throughout the period. The Early Ordovician was very hot due to intense greenhouse conditions and high carbon dioxide. However, the Earth eventually cooled. This led to the Hirnantian glaciation at the end of the period. As temperatures dropped, sea levels fell steadily for about 3 million years. This cooling caused the Ordovician–Silurian extinction events. Many creatures, including certain trilobites and cephalopods, were lost during these changes.