early atmosphere and oceans

earths first atmosphere

Earths first atmosphere was made of hydrogen and helium, the gases that were common in this region of the solar system as it was forming. Most of these gases were drawn into the center of the solar nebula to form the Sun. When Earth was new and very small, the solar wind blew off atmospheric gases that collected. If gases did collect, they were vaporized by impacts, especially from the impact that brought about the formation of the Moon. Eventually things started to settle down and gases began to collect. High heat in Earths early days meant that there were constant volcanic eruptions, which released gases from the mantle into the atmosphere (see opening image). Just as today, volcanic outgassing was a source of water vapor, carbon dioxide, small amounts of nitrogen, and other gases. Scientists have calculated that the amount of gas that collected to form the early atmosphere could not have come entirely from volcanic eruptions. Frequent impacts by asteroids and comets brought in gases and ices, including water, carbon dioxide, methane, ammonia, nitrogen, and other volatiles from elsewhere in the solar system (Figure Calculations also show that asteroids and comets cannot be responsible for all of the gases of the early atmosphere, so both impacts and outgassing were needed.


earths second atmosphere

The second atmosphere, which was the first to stay with the planet, formed from volcanic outgassing and comet ices. This atmosphere had lots of water vapor, carbon dioxide, nitrogen, and methane but almost no oxygen. Why was there so little oxygen? Plants produce oxygen when they photosynthesize but life had not yet begun or had not yet developed photosynthesis. In the early atmosphere, oxygen only appeared when sunlight split water molecules into hydrogen and oxygen and the oxygen accumulated in the atmosphere. Without oxygen, life was restricted to tiny simple organisms. Why is oxygen essential for most life on Earth? 1. Oxygen is needed to make ozone, a molecule made of three oxygen ions, O3 . Ozone collects in the atmospheric ozone layer and blocks harmful ultraviolet radiation from the Sun. Without an ozone layer, life in the early Earth was almost impossible. 2. Animals need oxygen to breathe. No animals would have been able to breathe in Earths early atmosphere.

uv protection

With more oxygen in the atmosphere, ultraviolet radiation could create ozone. With the formation of an ozone layer to protect the surface of the Earth from UV radiation, more complex life forms could evolve. Banded-iron formation. Click image to the left or use the URL below. URL:


bandediron formations

What evidence do scientists have that large quantities of oxygen entered the atmosphere? The iron contained in the rocks combined with the oxygen to form reddish iron oxides. By the beginning of the Proterozoic, banded-iron formations (BIFs) were forming. Banded-iron formations display alternating bands of iron oxide and iron-poor chert that probably represent a seasonal cycle of an aerobic and an anaerobic environment. The oldest BIFs are 3.7 billion years old, but they are very common during the Great Oxygenation Event 2.4 billion years ago (Figure 1.2). By 1.8 billion years ago, the amount of BIF declined. In recent times, the iron in these formations has been mined, and that explains the location of the auto industry in the upper Midwest.

earths third atmosphere

When photosynthesis evolved and spread around the planet, oxygen was released in abundance. The addition of oxygen is what created Earths third atmosphere. This event, which occurred about 2.5 billion years ago, is sometimes called the oxygen catastrophe because so many organisms died. Although entire species died out and went extinct, this event is also called the Great Oxygenation Event because it was a great opportunity. The organisms that survived developed a use for oxygen through cellular respiration, the process by which cells can obtain energy from organic molecules. This opened up many opportunities for organisms to evolve to fill different niches and many new types of organisms first appeared on Earth.

early oceans

The early atmosphere was rich in water vapor from volcanic eruptions and comets. When Earth was cool enough, water vapor condensed and rain began to fall. The water cycle began. Over millions of years enough precipitation collected that the first oceans could have formed as early as 4.2 to 4.4 billion years ago. Dissolved minerals carried by stream runoff made the early oceans salty. What geological evidence could there be for the presence of an early ocean? Marine sedimentary rocks can be dated back about 4 billion years. By the Archean, the planet was covered with oceans and the atmosphere was full of water vapor, carbon dioxide, nitrogen, and smaller amounts of other gases. Click image to the left or use the URL below. URL:

instructional diagrams

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earths first atmosphere was made of

a) nitrogen and oxygen

-->  b) hydrogen and helium

c) greenhouse gases

d) noble gases

gases from the early earth

a) were vaporized by the intense heat of the early earth and from impacts.

b) blew off in the intense solar wind.

c) were those that were drawn into the center of the solar nebula.

-->  d) all of the above

the gas that formed the early atmosphere came entirely from earths interior.

a) true

-->  b) false

in the early atmosphere, a lot of water vapor, carbon dioxide, methane, ammonia, nitrogen and other volatiles came from

a) the sun

b) the moon

-->  c) comets and asteroids

d) volcanic eruptions

the early atmosphere didnt have oxygen because plants had not yet evolved.

-->  a) true

b) false

for a long time there were only tiny simple organisms because

a) without oxygen there was no ozone layer.

b) without oxygen animals couldnt evolve.

c) evolutionary processes take a long time.

-->  d) all of the above.

__ in a cell that converts energy from nutrients to useable energy.

-->  a) cellular respiration

b) photosynthesis

c) cellular replication

d) none of the above

what do banded-iron formations represent?

a) the formation of rocks with a lot of iron.

b) the development of an anaerobic environment.

-->  c) the addition of large amounts of oxygen into the air.

d) all of these.

the great oxygenation event occurred when animals became common.

a) true

-->  b) false

diagram questions

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