(Pflueger )

Today’s Objectives Students will be able to: 1. Discuss how we have arrived at the current atmosphere from the original atmosphere. 2. Compare and Contrast the (3) major atmospheres and their compositions.

Origin of the Atmosphere Has our our atmosphere always been like it is today? …and here is some evidence why scientist think this. NO! The correct answer is NO!

4.6 Billion Years Ago The earliest atmosphere is believed to have been mainly… These were the 2 most abundant gases found in the early universe. Methane and AmmoniaMethane and Ammonia were also found at high levels. Hydrogen and Helium

Where did it go? It’s believed that this early atmosphere escaped into space. 1.Early Earth gravity too weak. 2.Earth without differentiated core, thus no magnetic field to deflect solar winds. 3.Heat of Earth and solar system. Why might this be the case?

As Things Got Older Eventually a second, more dense, atmosphere formed. volcanoes and steam vents. * This is assuming that volcanoes spewed out the same gases as they do today.*Gradually surrounded the Earth as gases escaped into the atmosphere from volcanoes and steam vents. * This is assuming that volcanoes spewed out the same gases as they do today.*

Atmosphere Part II Gases used from volcanism 80% water vapor (H 2 O) 10% carbon dioxide (CO 2 ) 4-6 % nitrogen (N 2 ) This continued on for millions of years!

Making of a Wet Day Millions of years of constant “outgassing” provides a rich supply of water vapor. During Achaean (DOMC - Haifi)

What Happened to the CO 2 Large amounts of CO 2 were dissolved into the oceans. Limestone. Through chemical and early biological processes, the CO 2 became locked up in carbonate sedimentary rocks, such as Limestone.

How Did We Get N 2 ? 1.Much of the water vapor condensed, either as clouds, rain, or ground water. 2.The concentration of CO 2 was quickly dwindling. 3.Nitrogen gradually built up. This is due to it being chemically inactive.

Then O 2 Made it Big Believed oxygen concentrated extremely slowly as: 1. Photochemical Dissociation: splitting of H 2 O by UV-rays. *The lighter hydrogen probably rose and escaped into space.* If O 2 levels 1-2% of current, would be enough to form O 3

Now We Have Life 2-3 billion 2. Enough oxygen accumulated for primitive plants to evolve, around 2-3 billion years ago. photosynthesisWith an increase in plant life, using photosynthesis, the atmosphere was greatly enriched with oxygen.

Evidence of an Early Atmosphere Precipitation of limestone 1. Precipitation of limestone in great quantities. oxidation of iron 2. The oxidation of iron to form banded deposits in early rocks. distribution of various minerals 3. The distribution of various minerals in most early sedimentary rocks.

Evidence of an Early Atmosphere Banded-iron Banded-iron Limestone b (Stone Museum)

Composition Today After 2-3 Billion years, the composition is much different today. There is more oxygen (that is a good thing) and a lot less carbon dioxide (also a good thing) Lets compare today with yester-year.

Nitrogen Oxygen Argon Carbon dioxide Water Vapor Ozone Other gases Composition Comparison Today 78 % 21%0.9%0.033%0-4% % < 1% Yester-Year4-6% < 1% 0-1%10%80%0%3-4% Today Yester-Year

Assignment For Thursday (Stimac)

Works Cited Department of Maritime Civilizations - University of Haifa. “Earth Origins and Formation.” 10 Apr Pflueger, Nathan. “The Origins of the Atmosphere.” 14 Oct Apr Stimac, John. “The Atmosphere – origin and structure.” 11 Apr Stone Museum. “Types of Rock.” 10 Apr