Jurassic

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The Jurassic was a middle period of time on Earth.

It began after a big extinction event. This event happened when volcanoes erupted. The Jurassic was named after the Jura Mountains. These mountains have special rocks called limestone.

The world was very warm back then. There were no ice caps at the poles. Huge forests grew near the top and bottom of the world. On land, dinosaurs became the main animals. The first birds also appeared during this time. They grew from a type of dinosaur.

Other animals also changed. Early crabs, frogs, and lizards appeared. Small mammals also began to grow and change. In the sea, large reptiles lived in the water. These were called ichthyosaurs and plesiosaurs.

Plants like ferns and conifers grew everywhere. Many modern groups of trees first appeared then. The land was also changing. The big supercontinent Pangaea began to split into two pieces. One piece was called Laurasia. The other piece was called Gondwana.

The Jurassic was a major geologic period on Earth. It was the middle period of the Mesozoic Era. This time spanned from the end of the Triassic to the start of the Cretaceous.

Scientists use the term to describe a specific slice of Earth's history. It is part of the larger Phanerozoic Eon. The period is very important for understanding how life changed.

During this time, the world was very different. The supercontinent Pangaea began to split into two large landmasses. One piece was Laurasia in the north. The other piece was Gondwana in the south.

The climate was much warmer than it is today. There were no ice caps at the poles. Large forests grew even near the cold poles. However, large dry areas existed in the lower latitudes.

Life on land and in the sea changed a lot. Dinosaurs became the most common animals on land. The first birds also appeared by evolving from theropod dinosaurs.

In the oceans, marine reptiles like ichthyosaurs and plesiosaurs lived. Pterosaurs were the main animals flying in the sky.

Modern sharks, rays, and many types of fish also appeared. Even small mammals began to grow and change during this era.

People have studied these layers of Earth for a long time. A German naturalist named Alexander von Humboldt visited the Jura Mountains in 1795. He found special limestone rocks there.

In 1829, Alexandre Brongniart used the term "Jurassic" in a book. He named the rocks after the Jura mountain range. Later, Leopold von Buch divided the period into three parts in 1839. These were the Black, Brown, and White Jurassic.

Geologists divide the Jurassic into three main stages. These are the Early, Middle, and Late Jurassic.

They use fossils like ammonites to tell these times apart. Ammonites are sea creatures that help mark the start of a stage. For example, the Hettangian stage began around 201.4 million years ago. The very end of the Jurassic was about 143.1 million years ago.

This helps us map the history of our planet.

The Jurassic is a major geologic period in Earth's history. It is the middle period of the Mesozoic Era. This era is part of the larger Phanerozoic Eon. The Jurassic began after the Triassic Period ended. It lasted until the Cretaceous Period started around 143.1 million years ago.

Geologists study this time to understand how life and planets change. It is a vital chapter in the story of our world.

Earth's physical landscape changed significantly during this period. The massive supercontinent known as Pangaea began to rift apart. This process split the land into two smaller supercontinents. Laurasia formed in the north. Gondwana formed in the south.

The climate was much warmer than it is today. There were no ice caps at the poles. Forests grew even in very cold polar regions. However, large arid expanses existed in the lower latitudes.

Life on land underwent a massive transition. During the Triassic, dinosaurs shared the world with other groups. These included dinosauromorphs and pseudosuchian archosaurs. By the Jurassic, dinosaurs became the dominant animals on land. The first stem-group birds also appeared during this time. They evolved from a branch of theropod dinosaurs.

Small mammals also continued to change. One lineage called Mammaliaformes survived the end of the Triassic. This led to the emergence of the first crown group mammals.

The oceans and skies were also full of new life. Marine reptiles like ichthyosaurs and plesiosaurs lived in the seas.

In the air, pterosaurs were the dominant flying vertebrates. Modern sharks and rays first appeared and diversified. Near the end of the period, the first crown-group teleost fish appeared. These are the ancestors of most modern fish. Even land animals like lizards and frogs began to appear.

Plants also changed during the Jurassic. The flora was dominated by ferns and gymnosperms. This group includes conifers, many of which first appeared then. There were also extinct groups like the Bennettitales.

These plants provided the foundation for the entire ecosystem. The combination of warm weather and lush plants supported large animals. This created a very productive environment for many different species.

Humans have worked to name and organize this time. In 1795, Alexander von Humboldt studied the Jura Mountains. He found limestone that was different from other rocks.

In 1829, Alexandre Brongniart coined the term "Jurassic." He named it after the Jura mountain range. In 1839, Leopold von Buch divided the period into three parts. He called them the Black, Brown, and White Jurassic.

Later, scientists like Alcide d'Orbigny used fossils to create more precise stages.

Today, geologists divide the Jurassic into three epochs. These are the Early, Middle, and Late Jurassic. They also use a system of stages to mark specific time intervals.

Geologists often use ammonites as index fossils to define these stages. An index fossil is a specific creature used to mark a time. For example, the Hettangian stage began around 201.4 million years ago. The base of the Hettangian is marked by the ammonite Psiloceras spelae tirolicum.

This precise mapping helps us understand the exact sequence of Earth's history.