Devonian

A long time ago, the world changed.

Many fish lived in the sea. People call this the Age of Fishes. Some fish had strong jaws.

New green plants grew on land. They grew roots and leaves. These plants made big forests. Some small bugs also lived on land.

The world had big pieces of land. These lands moved closer together. This made big mountains grow. The world was a very busy place.

The Devonian was a long time in Earth's history. It lasted for 60.7 million years. This time is named after Devon in England.

Many things changed on land and in the sea. On land, plants began to spread. They grew leaves and true roots. These plants made huge coal forests.

Small animals like bugs also moved onto land.

In the ocean, fish were the stars. Many different kinds of fish lived there. Some fish had strong jaws. We call this time the Age of Fishes.

Armored fish called placoderms were very common. Some fish even began to grow strong fins. These fins helped them move toward life on land.

The world looked different then. There were large continents like Gondwana and Laurussia.

These lands moved closer together. This movement helped make big mountains.

At the end, things became hard for life. Two big extinction events happened. These events killed many sea animals. They also wiped out the placoderm fish and most coral reefs.

The Devonian was a very important time for life on Earth. It lasted for 60.7 million years during the Paleozoic era. This period began after the Silurian period ended. It lasted until the Carboniferous period started. Scientists named this time after Devon in South West England. This is where people first studied rocks from this era.

Some people also call it the "Age of Fishes." This name honors the many types of fish that grew during this time. Other people called it the "Old Red Age." This refers to red and brown rocks found in Great Britain.

Life on land changed in amazing ways during the Devonian. At first, plants called pteridophytes began to spread across dry land. These were free-sporing plants that helped form huge coal forests. Later, some plants grew leaves and true roots. By the end of the period, the first seed-bearing plants appeared. This big change is called the Silurian-Devonian Terrestrial Revolution.

Small animals like arthropods also moved onto land. These included many creatures like arachnids and hexapods. They became well-established early in this period.

In the oceans, fish became the most important animals. Jawed fish became very diverse during these millions of years. Armored fish called placoderms ruled almost every part of the water. Primitive sharks also became more common in the sea. Some fish, called tetrapodomorphs, began to change in a special way. Their strong fins slowly turned into limbs for walking. These were the ancestors of all four-limbed animals.

Other sea life like ammonites and trilobites were also present. Large coral reefs were very common in the warm seas.

The map of the world looked much different back then. A huge supercontinent called Gondwana sat in the south. It included places like Africa and South America. A medium continent called Laurussia was to the east.

These large lands began to move closer together. This movement caused big mountain-building events. In North America, the Acadian Orogeny helped build the Appalachian Mountains. In Europe, the Variscan Orogeny was also starting.

Even though life was growing, the end of the period was hard. Two big extinction events happened near the end of the Devonian. The first one started about 375 million years ago. It killed most reef systems and many jawless fishes. It also wiped out most trilobites and the placoderms.

A second extinction happened around 359 million years ago. This event finished off the calcite sponge reefs. It also ended the time of the placoderms forever.

These changes shaped the world that came next.

The Devonian is a major geologic period within the Paleozoic era. It spans 60.7 million years of Earth's history. This period began 419.2 million years ago at the end of the Silurian. It concluded 358.5 million years ago with the start of the Carboniferous. The Devonian is the fourth period of both the Paleozoic and Phanerozoic eons. Scientists named this system after Devon, a county in South West England. This is where researchers first studied rocks from this era.

During this time, life underwent a massive transformation on land. This process is called the Silurian-Devonian Terrestrial Revolution. Initially, free-sporing land plants, or pteridophytes, began to spread across dry land. These plants eventually formed massive coal forests that covered entire continents. By the middle of the period, many vascular plants evolved true roots and leaves. Toward the end of the Devonian, the first seed-bearing plants, known as pteridospermatophytes, appeared.

Small animals also moved onto land during this revolution. Arthropods like myriapods, arachnids, and hexapods became well-established early on.

In the oceans, the Devonian is often called the "Age of Fishes." This name reflects the incredible diversity of fish that evolved. Armored fish called placoderms dominated almost every aquatic environment. Meanwhile, cartilaginous fishes like primitive sharks became more numerous than in previous periods. A very important group called tetrapodomorphs also began to diverge. These were lobe-finned fish with robust, muscled pectoral and pelvic fins. Over time, these fins gradually evolved into forelimbs and hindlimbs. These fish were the ancestors of all four-limbed vertebrates, or tetrapods.

Marine ecosystems were complex and filled with various life forms. The first ammonites appeared, which are a subclass of cephalopod molluscs. Trilobites, brachiopods, and massive coral reefs remained very common. However, the period ended with two devastating extinction events. The Late Devonian extinction began approximately 375 million years ago. It severely affected marine life by killing most reef systems and jawless fishes. It also wiped out the placoderms and nearly all trilobites, except for the order Proetida.

A second extinction occurred around 359 million years ago. This event completed the destruction of calcite sponge reefs and all placoderms.

The geography of the Devonian world was dominated by large landmasses. The supercontinent Gondwana sat in the far south. It included modern South America, Africa, Australia, Antarctica, and India. To the north was the small continent of Siberia. A medium-sized continent called Laurussia sat to the east. Laurussia formed from the collision of Laurentia and Baltica. This collision caused major mountain-building events called orogenies. In North America, the Acadian Orogeny helped build the Appalachian Mountains. In Europe, the Variscan Orogeny was also beginning.

Climate during the Devonian was generally warm but varied by region. Some evidence suggests significant glaciers may have existed during the Early and Middle Devonian. In the Early Devonian, many areas like Siberia and North America were quite arid. However, Africa and South America experienced a warm temperate climate. The average surface temperature in the Early Devonian was about 16 °C. As new forests grew, they drew carbon dioxide out of the atmosphere. This process may have caused a cooling of about 5 °C during the Mid-Devonian.

The movement of continents and changing climates shaped the entire planet. Tectonic activity caused the Rheic Ocean to close. It also caused the separation of South China from Gondwana. This movement helped expand the Paleo-Tethys Ocean. These massive changes set the stage for the later formation of Pangaea. The Devonian shows how life, land, and atmosphere are all connected. The evolution of plants and fish changed the very chemistry of the Earth. This period remains a vital chapter in the story of our living world.