|Daley, B. Robert, John W. Highman & George F. Mathis. Earth Science: A Study of a Changing Planet. 1978: 450.||"Notice that Pre-cambrian time begins with the origin of the earth, about 4.5 billion years ago and ends about 570 million years ago."||4.5 Gyr|
|"4,500 million years ago"||4.5 Gyr|
|World Book Multimedia Encyclopedia. Chicago: World Book, 1996.||"Rocks of the Archeon eon contain the earliest fossils, which are about 3½ billion years old."||3.5 Gyr|
|Reader, John. The Rise of Life: The First 3.5 Billion Years. 1986: 29.||"The Pre-Cambrian encompasses nearly 90% of the Earth's history, stretching from 4.5 billion years ago, to 570 million years ago when the fossil evidence first reveals living cells."||4.5 Gyr|
|"The Planet Earth." The World Book Encyclopedia of Science. Chicago: World Book, 1986.||"… no more than 4.5 billion years ago …."||4.5 Gyr|
It is said that we are very lucky to be alive, that if the Planet Earth wasn't positioned as perfectly as it is now, we wouldn't be able to survive.
According to Aristotle, "Life in the first instance, is formed by the inherent energy of the primary elements such as: Earth, Water, Air and Fire which molds and organizes inert matter into living things."Some examples of this idea are fireflies developed from the morning dew, bedbugs and lice developed from the slime of wells and mice along with some higher animals came from moist soil. Aristotle also felt that humans first appeared on Earth in the form of a worm.
After researching this topic, I have been given a broader mental picture of how life began. Between 3.5 and 4.5 billion years ago there was enough dust and gas to condense into one planet, the planet earth. Shortly after, life arose. From that time until about 570 million years ago was known as the Precambrian Era. Then came the Paleozoic Era in which other forms of life were derived. About 225 million years ago began the Mesozoic Era (the age of reptiles). It was followed by the most recent era, the cenozoic Era.
This is a very controversial topic, especially for those who didn't have the equipment we have today. Just because there were no fossils 4.5 billion years ago, does that mean there was no life? Of course not. It has been a gradual process to get to life, as we know it today, a life that only took 1/750,000 of the total record however the life that takes about 90% of our existence today is the one we know least about.
Ron Huggins -- 1997