The Precambrian is the first time period of the earth. The earth took form about 4.5 billion years ago. For the first 4 billion years of that time, the Earth was growing and changing. The only living things during this time were one-celled organisms.
The Hadean Time actually came first, but it is not a geologic time period. It was the time when the earth was molten and had not yet formed a crust. It is not a geologic time because there were no rocks yet.
The Precambrian is divided into two parts: the Archaen time and the Proterozoic Era. There may not have been many different forms of life, but very important work was being done during the Precambrian.
First, the Earth formed. The outer covering of the earth cooled and hardened into a crust. The hot molten insides of the Earth leaked out at weak places in the crust. These volcanoes created more rock surface on the young Earth. The clouds formed by the volcanoes caused huge amounts of rain to fall and the oceans were created.
The Cooling Crust
When the crust cooled, huge pieces of the crust began to move in different directions. These are called tectonic plates. The tectonic plates still move around on the surface of the earth today. They bump and push against each other. Sometimes the edge of one plate moves under the edge of another. This causes the continents to move around and change shape. This movement has been going on since the formation of the earth's crust.
The first continent was huge. It is called Rhodinia. It formed about 1.1 billion years ago. Rhodinia contained the modern-day continents. North America was in the middle. South America, Australia and Antarctica were all around North America.
About 350 million years later, the first ocean formed around Rhodinia. It caused the supercontinent to break into two parts. The part that contained North America moved toward the South Pole. The rest of Rhodinia moved toward the north. 150 million years later they collided again to form a new super continent,Pannotia.
The first life formed. This was not cell life as we know it, but it was life just the same. The oceans were not like the oceans of today. Some say they were thick like soup. The chemistry of the oceans made them the perfect place for life to begin.
The first one-celled organisms formed during the Precambrian Era. They had an important job to do. They helped make the air and water around the Earth full of oxygen. Once there was plenty of oxygen, new life could form. This life would have many cells together to make different kinds of animals.
All of the important work of the Precambrian made the Earth ready for what would come next. A new Era was about to begin: the Paleozoic Era. There was an explosion of life forms in the next period. It is called the Cambrian Period.
Return to Geologic Time Line
Learn more about the Precambrian Era