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The Origin of Life on Earth


The image is of a seagull, a member of the animal kingdom.
Image courtesy of Corel Photography
At one time or another, we've probably all wondered how life first got started. This is not an easy question! There are at least three kinds of explanations for how life on Earth began:

1) Life was created. Some people believe that life on Earth was created by a supreme being or spirit. These ideas have been around for a very long time and differ among different cultures and religions. We can't use science to test these ideas, so we leave it to each person to decide for him- or herself.

2) Life began somewhere else in the universe, then arrived on Earth later, such as with the crash of a comet.

3) Life began on Earth by chance. Many scientists believe that life began as the result of complex chemical reactions that took place in the Earth's atmosphere 3.5 billion years ago. When chemicals in the atmosphere interacted with the electricity from lightning, certain substances formed that were necessary for early forms of life. In the 1950's, two biochemists conducted an experiment which showed how this could happen in the laboratory.

The Origin of Life on Earth


The image is of a seagull, a member of the animal kingdom.
Image courtesy of Corel Photography
How did life begin on Earth? Though no one is ever likely to know the whole story, virtually everyone has wondered at one time or another, how life on Earth began.

There are at least three types of hypotheses which attempt to explain the origin of life on Earth. The first and oldest of these hypotheses suggest that life was created by a supreme being or spiritual force. Most cultures and religions have their own explanations of creation that are passed down from generation to generation. Because these ideas cannot be proved nor disproved, we consider them outside the boundaries of science. For that reason, they will not be pursued here and are left to each individual to decide.

The second set of hypotheses suggest that life began in another part of the universe and arrived on Earth by chance, such as with the crash of a comet or meteor.

The third, and most common hypothesis in the scientific community, is that life began approximately 3.5 billion years ago as the result of a complex sequence of chemical reactions that took place spontaneously in Earth's atmosphere. In the 1950's, two biochemists conducted an experiment which showed that certain molecules of life (amino acids) could form spontaneously when the conditions of Earth's early atmosphere were recreated in the lab. It is assumed that over time, these molecules interacted with one another eventually leading to the earliest forms of life.

The Origin of Life on Earth


The image is of a seagull, a member of the animal kingdom.
Image courtesy of Corel Photography
How did it all begin? Perhaps the most intriguing question we, as human beings, could ever contemplate is that of our own origin.

At least three classes of hypotheses exist attempting to explain the origin of life on Earth. The first, and oldest of these suggest that life was created by a supreme being or spiritual force. These ideas and explanations have been passed down from generation to generation and vary considerably among different cultures and religions. Because theories about creation can neither be proved nor disproved, they lie outside the realm of science and will not be pursued further in these pages. We leave it to each individual to decide for him- or herself.

The second set of hypotheses suggest that life began elsewhere in the universe and "arrived" on Earth by chance, such as with the crash of a comet or meteor.

The third, and most widely held hypothesis in the scientific community, is that life on Earth arose approximately 3.5 - 4 billion years ago as the result of a very specific sequence of random chemical events. This theory suggests that the early environment of Earth may have provided the appropriate conditions for the spontaneous formation of organic molecules--the building blocks of life. In the early 1950's two biochemists, Stanley Miller and Harold Urey, conducted an experiment which demonstrated the spontaneous formation of amino acids from inorganic precursors in the lab. It is assumed that over time, the early organic molecules interacted, eventually leading to the evolution of the first life forms.



Last modified January 17, 1999 by the Windows Team

The source of this material is Windows to the Universe, at http://www.windows.ucar.edu/ at the University Corporation for Atmospheric Research (UCAR). ©1995-1999, 2000 The Regents of the University of Michigan; ©2000-05 University Corporation for Atmospheric Research. All Rights Reserved. Site policies and disclaimer