Evolution Fact and Theory and the Origins of Life

Revision 8
© 2007-2015 by Zack Smith. All rights reserved.


What is evolution?

It is two things: The fact of evolution and the hypotheses surrounding how evolution works. The hypotheses are collectively known as the theory of evolution.

The fact of evolution

Evolution is defined simply as genetic change over time, meaning more precisely between generations. Examples of genetic change over time are extremely easy to identify. Every year we observe new flu viruses and new bacterial strains. This is evolution. Every human has slightly different genes from his or her parents. That is evolution, too.

The theory of evolution

There are numerous hypotheses about how evolution occurs. These hypotheses are generally supported by enormous amounts of evidence, both observational evidence and experimental evidence. In science, when a set of hypotheses are related and supported by evidence, we call this collection of evidence and hypothese a scientific theory, or simply theory for short.

Note how term theory in science means something different than in everyday English. A scientific theory is not the same thing as a theory in the common dictionary sense. One word can have multiple different or related meanings. Does belief in religion means the same as belief about what color your car is? No.

Origins of Life

The Earth is 4.5 billion years old. The Earth's crust ws stable at 3.9 billion years ago.

Profile of the Early Earth

It was a very different world than what we know today. There was:

  • No oxygen (O2)
  • Much ultraviolet light (UV) because there was no ozone layer (O3) for protection
  • Strong winds
  • Hot weather
  • Much lightning
  • Plus gases from volcanoes

The atmosphere at the time was comprised of methane, ammonia, water, and carbon dioxide (CO2).

The origin of life can be summarized by saying that basically, simple molecules combined with UV and lightning to create simple organic compounds that are the constituents of life. This combination has been simulated in the lab, proving that it is a plausible hypothesis.

Chemical evolution

Aleksandr I. Oparin (Russian) and Haldane (English) in 1920 proposed that life could arise from prebiotic soup i.e. oceans.

Oparin argued that new life doesn't arise today because O2 attacks chemical bonds and the ozone layer prevents sufficient heat, lightning, and UV.

But back then, basic chemicals, subjected to the harsh early Earth environment, formed into the basic molecules of life.

Four stages of chemical evolution (proven in the lab), called the Oparin-Haldane model: