Early Atmosphere and Oceans Study Guide

Earth’s atmosphere can be divided into three stages, so try to memorize dates based on the events during each stage.

Conditions of the Early Earth

The first atmosphere consisted of hydrogen and helium, gasses predominantly found throughout the solar system
When Earth was cool enough, water vapor from outgassing and comets condensed and rain began to fall (this initiated the water cycle).
Outgassing brought gasses from the interior of the Earth to the surface.

Earth’s atmosphere can be divided into three stages, so try to memorize dates based on the events during each stage.

Impacts by asteroids and comets brought carbon dioxide, methane, ammonia, nitrogen, and other explosive substances.
Precipitation collected over millions of years to form the first oceans.
Dissolved minerals carried by stream runoff made the early oceans salty.
4 billion year old marine sedimentary rocks give evidence to a presence of an early ocean

Atmosphere

Description

First Atmosphere

Primarily made of hydrogen and helium
Outgassing was a source of water vapor, carbon dioxide, small amounts of nitrogen, and other gases.

Second Atmosphere

First atmosphere to stay with the planet
This atmosphere had lots of water vapor, carbon dioxide, nitrogen, and methane but almost no oxygen.

Third Atmosphere

The Great Oxygenation Event introduces free oxygen into the atmosphere and causes the extinction of many organisms
Banded-Iron formations give evidence to an oxygen filled atmosphere 3.7 billion years ago
Formation of Earth’s ozone layer from excess oxygen produced by plants