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Earth has had three atmospheres

Leif RømckeSep 20, 2020, 6:59:12 AM

What is the history of the Earth's atmosphere? The earth has had three atmospheres, with different chemical composition. On the surface of the sun, X = 73.81%, Y = 24.85% and Z = 1.34%.

Time scales

The universe is 13.7 billion years old. The earth is approx. 4.6 billion years old, not 6,000 years old. Now 4.6 billion is the same as 4,600,000,000, which is very much more than 6,000. A lifetime of us homo sapiens becomes microscopic in relation to an expected lifetime of the sun, which is approx. 10 billion years.

H and He

The first of Earth's atmospheres was formed about 4.57 billion years ago. Back then, our planet was still very young. The atmosphere consisted of hydrogen and helium. According to a geological time scale, this atmosphere was short-lived.

How do we know today that the atmosphere at that time consisted only of these two elements? Simply because the universe today consists almost exclusively of H atoms and He atoms. When the universe, after the Big Bang, became transparent, matter consisted only of these elements. The other elements were made only when stars appeared. After some stars have exploded, the interstellar gas and dust now also consist of other elements - in small amounts.

The quantities are so small that astronomers call them metals, although it is not strictly just metals. We might call them "other". Astronomers have given the "other" symbol Z. The amount of hydrogen is called X and varies between 70% to 80%. The amount of helium is called Y and is then 20% to 30%, depending on the time and place in the Universe. Z is only a few percent.

The strange thing is that there are planets like Mercury, Venus, Earth and Mars. The four outermost planets are gas planets. They consist mainly of gases such as hydrogen and helium, and have a much larger mass than the four rocky planets. The rocky planets and we consist, almost exclusively, of the famous elements "other". (No, Pluto is no longer considered a planet.)

CO2 and H2O

About 4.4 billion years ago, the earth's crust solidified. Many volcanoes were formed. During volcanic eruptions, these emitted water vapor, carbon dioxide and ammonia into the atmosphere. Over time, the density of the volcanic gases CO2 and H2O became sufficient to form the Earth's second atmosphere. Some nitrogen was present, but hardly any free oxygen. This is somewhat reminiscent of Venus' current atmosphere, which is 96.5% carbon dioxide and 3.5% nitrogen.

The Earth's atmosphere began to change slowly as carbon dioxide was dissolved in the oceans and precipitated as carbonates. This then set the stage for the first and only life in the universe we know of today.

Life arises

3.5 billion years ago, life appeared in the form of microbes. About 2.7 billion years ago, they were joined by microbes called cyanobacteria. Cyanobacteria (blue-green algae) were the first oxygen-producing phototropic organisms. They slowly began to absorb carbon dioxide from the atmosphere and release oxygen.

The oxidation event is sometimes considered a disaster. Oxygen was poisonous to most life forms on Earth at that time. The oxygen disaster is the first major mass extinctions on the planet. The advantage for us is that we got the third of the earth's atmosphere. We need it to survive today.

A dynamic atmosphere in a dynamic universe

The transition between the earth's three atmospheres is not like flipping through a picture book. We have an atmosphere, then we turn a pege and then we have the next atmosphere. Atmospheres change dynamically all the time.

Water, H2O, is a molecule with two hydrogen atoms. Except for water, we consist of Z. We want stability, but we would not have existed if the Earth were immutable. We also live in a time in the history of mankind where changes happen so fast that they are noticeable in our lifetime. It is therefore naive to believe that if we limit human CO2 emissions to the atmosphere, then our world will be stable.

It is estimated that we on Earth have 1300-1500 volcanoes that have erupted over the last 10,000 years. How much emissions come from today's volcanoes? The Pinatubo volcano has had large eruptions around 500, 3000 and 5500 years ago. On June 15, 1991, millions of tons of sulfur dioxide were released into the atmosphere, resulting in a reduction in global temperatures over the next few years.