The Origins Of Earth

Earth is the only planet we know of that can support life. This is an amazing fact, considering that it is made out of the same matter as other planets in our solar system, was formed at the same time and through the same processes as every other planet, and gets its energy from the sun.

To a universal traveler, Earth may seem to be a harmless little planet in the far reaches of one of billions of spiral galaxies in the universe. It has an average size star of average brightness and is joined by seven other planets — which support no known life forms — in its solar system. While this may be fitting for a passage from The Hitchhikers Guide to the Galaxy, by Douglas Adams, in the grand scheme of the universe, it would be a fairly accurate description.

However, Earth is a planet teeming with vitality and is home to billions of plants and animals that share a common evolutionary track. How and why did we get here? What processes had to take place for this to happen? And where do we go from here? The fact is, no one has been able to come close to knowing exactly what led to the origins of life, and we may never know. After 5 billion years of Earth’s formation and evolution, the evidence may have been lost. But scientists have made significant progress in understanding what chemical processes that may have led to the origins of life.

There are many theories, but most have the same general perspective of how things came to be the way they are. Following is an account of life’s beginnings based on some of the leading research and theories related to the subject, and of course, fossil records dating back as far as 3.5 billion years ago.

Earth began to form over 4.6 billion years ago from the same cloud of gas (mostly hydrogen and helium) and interstellar dust that formed our sun, the rest of the solar system and even our galaxy. In fact, Earth is still forming and cooling from the galactic implosion that created the other stars and planetary systems in our galaxy. This process began about 13.6 billion years ago when the Milky Way Galaxy began to form.

As our solar system began to come together, the sun formed within a cloud of dust and gas that continued to shrink in upon itself by its own gravitational forces. This caused it to undergo the fusion process and give off light, heat and other radiation. During this process, the remaining clouds of gas and dust that surrounded the sun began to form into smaller lumps called planetesimals, which eventually formed into the planets we know today.

PlanetesimalsA large number of small objects, called planetesimals, began to form around the Sun early in the formation of the solar system. These objects were the building blocks for the planets that exist today. (NASA graphic, by N. A. Cabrol.)

The Earth went through a period of catastrophic and intense formation during its earliest beginnings 4.6-4.4 billion years ago. By 3.8 to 4.1 billion years ago, Earth had become a planet with an atmosphere (not like our atmosphere today) and an ocean. This period of Earth’s formation is referred to as the pre-Cambrian Period. The pre-Cambrian is divided into three parts: the Hadean, Archean and Proterozoic Periods.

Pre-Cambrian Period

The Earth formed under so much heat and pressure that it formed as a molten planet. For nearly the first billion years of formation (4.5 to 3.8 billion years ago) — called the Hadean Period (or hellish period) — Earth was bombarded continuously by the remnants of the dust and debris — like asteroids, meteors and comets — until it formed into a solid sphere, pulled into orbit around the sun and began to cool down.

By Eric McLamb