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The Origin of Life on Earth

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.

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Traveling Nitrogen is a fun group game appropriate for the classroom. Players follow nitrogen atoms through living and nonliving parts of the nitrogen cycle. For grades 5-9.

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Traveling Nitrogen Classroom Activity Kit

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The First Living Cells

The first beings were probably much like coacervates. As a group, these bacteria are called heterotrophic anaerobes (ann-air-robes). Because there was virtually no oxygen in the atmosphere at this time,...more

Can there be Life in the Environment of Jupiter?

Jupiter's atmospheric environment is one of strong gravity, high pressure, strong winds, from 225 miles per hour to 1000 miles per hour, and cold temperatures of -270 degrees to +32 degrees (freezing temperature)....more

The possible discovery of Life on Mars

In July, 1996, it was announced that Dr. David McKay, along with a team of scientists at Johnson Space Center (a division of NASA), had discovered possible fossils of bacteria in a meteorite named ALH84...more

The Environment of Saturn

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Can there be Life in the Environment of Titan?

Titan's atmosphere is a lot like the Earth's, except that it is very cold, from -330 degrees to -290 degrees! Like the Earth, there is a lot of Nitrogen and other complex molecules. There also may be an...more

Autotrophs

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Coacervates

In the warm primordial ocean, aggregates of amino acids, proteins, and other hydrocarbons came together into a form called *coacervates*. Amino acids will spontaneously form coacervates in the same way...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part by the National Science Foundation and NASA, our Founding Partners (the American Geophysical Union and American Geosciences Institute) as well as through Institutional, Contributing, and Affiliate Partners, individual memberships and generous donors. Thank you for your support! NASA AGU AGI NSF