How did the Earth Get to Look Like This?

Key points in the formation of the earth:

• Formed via acretion of grains in a 4-step process
  • step 1
  • step 2
  • step 3
  • step 4
• Original Protoearth was molten
• dense material (molten nickel and iron) flowed to the center
• lighter material (molten silicon) flows to the top
• earth cools and solidifies into basic core, mantle and crust structure
• Overall density of the earth is 5.5 grams per cubic centimeter
• The earth has a lot of trapped gasses in its interior

The original atmosphere of the Earth, Venus and Mars consisted of Hydrogen and Helium. Those light elements, however, were heated to escape velocity by solar radiation and thus this atmosphere escaped. The current atmospheres of the Earth, Venus and Mars are therefore secondary and evolved from other processes.

Overview of Atmospheric Compositions:

• Venus --> Atmosphere is almost entirely Carbon Dioxide. Atmospheric pressure is 90 times that of the Earth. There is a lot of Carbon Dioxide present.
• Earth --> Atmosphere is essentially 75% Nitrogen and 25% Oxygen. Where did the Carbon Dioxide go?
• Mars --> Atmosphere is almost entirely Carbon Dioxide but there is not much of it now. Atmospheric pressure is about 1% that of the Earth's.

Outgassing --> Early Formation of the Earth's Atmosphere

Present day composition of volcanoe effluents:

• Water Vapor --> 50--60%
• Carbon Dioxide --> 24%
• Sulfur --> 13%
• Nitrogen --> 5.7%
• Argon --> 0.3%
• Chlorine --> 0.1%

It is likely that there was NOT enough water released via outgassing to account for the present day oceans

Most of the water was likely delivered to the earth after it formed via collisions with left over planetisimals and cometisimals. The influence of Jupiter on the orbits of leftover cometisimals may well be key.

Tidal forces from a newly formed moon may also be key in promoting first stages of development of life as well.

Hence the earth may need both Jupiter and the Moon if it is to ask a question sometime later.

Formation of Planetary Atmospheres:

• Condensation of water vapor is crucial
• Main steps in evolution of the Earth's Atmosphere
• On this planet it was too cold for water vapor to condense. Hence the atmosphere is all Carbon Dioxide
• On this planet it was too hot for water vapor to condense. Hence the atmosphere is all Carbon Dioxide
• On this planet it was just right. The carbon dioxide content of the earth's atmosphere is now all locked up in rocks.

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