Science 52

Life on Earth is thought to have occurred over a billion year ago (BYA). Scientists are certain that the conditions of early Earth were far harsher than those of Earth today. There was no atmosphere, so high levels of UV radiation reached Earth’s surface. Temperatures were extreme, lightening storms and volcanic eruptions were frequent. Methane and sulfur, rather than oxygen and nitrogen, formed a noxious gaseous layer above Earth’s crust.

Two scientists debate how life first evolved.

Scientist 1

The first organisms on Earth were made of simple organic molecules, and were heterotrophic, requiring food to manifest energy. Most likely, these organisms were formed as chemicals liquified then dried quickly in the intense heat. The UV radiation would have caused rapid mutations in any life form, so diversity may have occurred rather quickly. Eventually, a mutation occurred that allowed for organisms to produce their own food (autotrophism). These organisms would have produced large amounts of oxygen and helped to form the modern day atmosphere.

Scientist 2

Life, as classified by modern scientists, could not exist on Earth until there were large quantities of liquid water. However, since the temperatures of early Earth were so extreme, probably due to the high levels of UV radiation, liquid water was scarce, if at all present. The earliest life forms must have been similar to bacteria that use chemicals to produce their own food. Eventually, a mutation occurred that allowed these organisms to use sunlight to produce food. These organisms would have released large amounts of oxygen, forming an early atmosphere and allowing the Earth to cool. Eventually, water pools formed and life on Earth diversified.