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Science, Evolution, and Creationism, by the National Academies, focuses on teaching evolution in today's classrooms. Check out the other publications in our online store.
This is an image of Mt. St. Helens, in Washington, USA.
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Image from: USGS, courtesy of Volcano World

Earth's Secondary Atmosphere

The atmosphere is a collection of gases, and constitutes the air we breathe. The air we breathe today is made mostly of Nitrogen and Oxygen but also Hydrogen, Helium, water vapor, carbon dioxide, sulfur dioxide, methane, ammonia, and many other gases including smog from human activities. Scientists think that the atmosphere we breathe today is nothing like the atmosphere the Earth started with. In fact scientists think that 99% of today's atmosphere is new compared to the original air. Thus scientists call the atmosphere of today a secondary atmosphere.

Scientists think that the secondary atmosphere came from the many volcanic eruptions which took place in Earth's early history, and which continue today. All volcanoes are different but in general they release gases such as H2O, CO2, SO2, H2S, HCl, N2, NO2. These gases come from the melting of the Earth's crust at subterranian depths. In fact, volcanic activity can be thought of as recycling and replenishing the molecules of the atmosphere. These molecules are not the Nitrogen and Oxygen which are the majority of gases in the air today, however. So you may ask, "where did they come from?"

The formation of the early ocean played a large part in shaping what gases remained in the atmosphere and what gases are carried into the water. Scientists think that the Earth's secondary atmosphere may have come to be dominated by N2 because it alone of all the gases comprising the secondary atmosphere does not readily dissolve in water. Oxygen came into the atmosphere as a waste product from the photosynthetic activity of early life forms after that oxygen had first combined with residual surface iron to produce iron ore.

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Earth's Primordial Atmosphere

Scientists ask many questions. One of the questions they like to ask is "Where did the atmosphere come from?" As always, scientists chip in with many different, and sometimes conflicting answers. Some...more


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Earth's Early Ocean

Once the Earth began to cool, water vapor, one of the volatiles, began to condense and form an ocean. According to the Goldilocks theory, Earth is at just the right distance from the sun for the temperature...more

Early Life

Over a very long time, gradual changes in the earliest cells gave rise to new life forms. These new cells were very different from earlier cells because they were able to get their energy from a different...more

Iron Ore Deposits

Eventually, photosynthesis by the earliest forms of plant life (a form of life capable of feeding itself instead of feeding off of others) began to produce significant amounts of oxygen. One important...more

The Archean

The Archean is the name of the age which began with the forming Earth. This period of Earth's history lasted a long time, 2.8 billion years! That is more than half the expected age of the Earth! And no...more

Salts in the Earth's early ocean

We all know that today ocean waters are very salty. There aren't many sedimentary rocks older than 2.5 billion years (see geologic time) that means that there must have been mostly igneous rocks at the...more

The Triassic

This period of time in Earth's history is a period when dinosaurs roamed the Earth. This period lasted 37 Million years. During this time, the continents we know today were combined into a giant continent...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA