The Precambrian Period is the first geologic 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. During the Precambrian, the most important events in biological history took place. Consider that the Earth formed, life arose, the first tectonic plates arose and began to move, eukaryotic cells evolved, the atmosphere became enriched in oxygen and just before the end of the Precambrian, complex multicellular organisms, including the first animals, evolved.
This was also a time characterized by great volcanic activity, but it is mostly shrouded in mystery. What we do know is that the volcanoes were a result of water and sediment carried down by the slab of ocean crust caused the mantle to melt and rise up, punching through the crust above and erupting as volcanoes. They would have been powerfully explosive volcanoes, full of gas and water, just like a shaken can of soda when you open it. These eruptions continued for millions of years, building up layer upon layer of lava and ash, thousands of meters thick. We know that the first hard-shelled creatures evolved approximately 900 million years ago as well. It wasn’t until 650 million years ago that multi-celled animals were present on the planet.
The atmosphere of the early Precambrian Earth is poorly known, but is thought to have contained very little oxygen. It appears that many materials whose oxides are insoluble were present in the oceans for a few billion years after the Earth’s creation. It is thought that life evolved, and developed the ability to create organic compounds from water and carbon dioxide. Oxygen was freed in the process. The oxygen was immediately tied up in chemical reactions with various materials until the supply of iron ran out. After that the modern high-oxygen atmosphere developed. Older rocks contain massive Banded Iron Formations that were apparently laid down as iron and oxygen combined.
What is surprising about the Precambrian Period is that we know so little about it, even though it consumes roughly 7/8 of the time span of the earth. This is because the period took place millions and billions of years ago, so researching this time has proved difficult. There is very little evidence remaining from this time as far as fossil records go. Archaeologists can find few traces of life in the Precambrian.
