Ediacaran

A long time ago, the Earth changed.

Big ice covered much of the world. Then the ice melted away. This let many new living things grow.

These creatures lived in the sea. Most had soft bodies. They did not have hard shells. Some looked like worms or fronds. Some even looked like disks.

Some of these animals were very simple. They are now gone. Other animals were like things we see today. Some were like sponges. Others were like sea creatures with soft bodies.

We find their shapes in rocks. These are called fossils. We find them in a place called South Australia. They help us see how life began.

It is a grand story of life.

The Ediacaran was a long time in Earth's history.

It lasted for 96 million years. It began 635 million years ago. It ended 538.8 million years ago.

This period started after a time of great ice. The world was covered in ice called a glaciation. When the ice melted, life changed quickly. This is called the Avalon Explosion. Many new living things appeared in the sea.

Most of these creatures had soft bodies. They did not have hard shells. Some looked like worms or fronds. Others looked like disks or bags. Many of these animals are now extinct. This means they no longer live on Earth.

Some creatures were like animals we see today. These include cnidarians, which are soft-bodied sea animals. We also see early versions of molluscs.

We find fossils of these creatures in South Australia. A man named Reg Sprigg found them in 1946.

These fossils help us study how life grew. They show us the start of complex life.

The Ediacaran was a very special time in Earth's history.

It lasted for about 96 million years. This period began 635 million years ago. It ended 538.8 million years ago. It was the last part of the Proterozoic Eon. This time was important because it led to the Cambrian Period. After this, recognizable fossils of life became much more common. The Ediacaran shows us how life began to grow in new ways.

This period started after a huge ice age ended. Scientists call this global glaciation the Snowball Earth. When the ice melted, a sudden burst of life happened. This event is called the Avalon Explosion. Many new living things appeared in the sea around 575 million years ago. These creatures were often soft-bodied animals. They did not have hard shells like many animals today.

Geologists first found these amazing fossils in South Australia. A man named Reg Sprigg discovered them in 1946. He found them in the Ediacara Hills. These fossils belong to a group called the Ediacaran biota. The period is named after these specific hills. In 2004, the official name for this period was approved. It was the first new geological period named in 120 years.

There were many different kinds of life during this time. Some animals were shaped like disks or bags. Others looked like segmented worms or sea fronds. One group was called Proarticulata, which included animals like Dickinsonia. Another group called Petalonamae looked like sea pens. There were also animals with three-way symmetry called Trilobozoa.

Some creatures, like Kimberella, were like early molluscs. These living things were very different from life today.

We can study this time by looking at rocks. The start of the Ediacaran is marked by a special layer of rock. This is called a cap carbonate. It sits right on top of old glacial deposits. This layer shows that the climate changed very quickly. During this period, a huge landmass called Pannotia formed and broke apart. Scientists use many different tools to date these old rocks. They study the chemistry of the earth to understand the past.

The Ediacaran is a major geological period in Earth's history. It belongs to the Neoproterozoic Era. This period lasted for approximately 96 million years. It began 635 million years ago at the end of the Cryogenian Period. It ended 538.8 million years ago at the start of the Cambrian Period. This era is the final part of the Proterozoic Eon. It is also the last part of the Precambrian supereon. This period is vital because it marks the rise of complex life. Before this, life was much simpler. After this, recognizable fossil evidence of life becomes common in the Phanerozoic Eon.

The period began following a massive global glaciation. Scientists often call this event "Snowball Earth." As the ice melted, a sudden evolutionary event occurred. This is known as the Avalon Explosion. Around 575 million years ago, many new lifeforms appeared. This was a radiation event where complex multicellular fauna became widespread. Most of these organisms were soft-bodied. They did not have hard shells or skeletons. Most of these unique creatures died out during the End-Ediacaran extinction event 539 million years ago. This transition shows how life responds to massive changes in the environment.

Scientists classify the Ediacaran biota into several distinct groups. One group is the Proarticulata. These were bilaterians with simple articulation, such as *Dickinsonia* and *Spriggina*. Another group is the Petalonamae. These animals resembled sea pens, like the fossil *Charnia*. Some animals had radial shapes, such as the *Aspidella* group. There were also Trilobozoa, which had tri-radial symmetry. An example of this is *Tribrachidium*. Some creatures were even more similar to modern animals. These included early cnidarians and early bilaterians. A mollusc-like creature called *Kimberella* also lived during this time. Later in the period, hard-bodied organisms with mineralized shells began to appear.

The history of this period is tied to a famous discovery. Geologist Reg Sprigg discovered trace fossils in 1946. He found them in the Ediacara Hills of South Australia. These fossils belonged to a diverse community of unrecognized lifeforms. The period takes its name from these hills. However, the official type section is located elsewhere. It is in the Enorama Creek section within the Brachina Gorge. This site is in the Ikara-Flinders Ranges National Park. In 2004, the International Union of Geological Sciences ratified the period. This was the first new geological period declared in 120 years.

Geologists define the start of the Ediacaran using specific markers. The lower boundary is marked by a "cap carbonate." This is a chemically distinctive layer of rock. It sits directly on top of glacial deposits. This layer shows an unusual depletion of the isotope 13C. This chemical change indicates a sudden shift in the climate. The upper boundary is defined differently. It is marked by the first appearance of the trace fossil *Treptichnus pedum*. This fossil is a type of bioturbation, which is a disturbance of sediment by living things. Scientists use these different methods to track the passage of deep time.

Several major geological events happened during these millions of years. The supercontinent Pannotia formed and then broke apart. The Earth also experienced other glaciation events. These include the Gaskiers and Baykonurian glaciations. There was also a chemical event called the Shuram excursion. While the Shuram excursion is a major feature, its glacial origin is unlikely. The age of the rocks is determined through complex dating. Scientists use uranium-lead and rhenium-osmium dating. They apply these methods to rocks in Africa, China, North America, and Tasmania. This helps them build a global timeline for the Ediacaran.

The Ediacaran connects many different scientific fields. It links biology with geology and chemistry. We see how biological evolution follows climate changes. We see how the movement of continents affects life. The period serves as a bridge to the Cambrian explosion. It represents the transition from a world of simple microbes to a world of complex animals. Understanding the Ediacaran helps us understand the history of all life on Earth. It shows us the very first steps of the complex creatures we see today.