- Created by: lx1234
- Created on: 07-03-18 23:11
Gases in the early atmosphere
Scientists believe that the Earth was formed about 4.5 billion years ago. Its early atmosphere was probably formed from the gases given out by volcanoes. It is believed that there was intense volcanic activity for the first billion years of the Earth's existence.
The early atmosphere was probably mostly carbon dioxide with little or no oxygen. There were smaller proportions of water vapour, ammonia and methane. As the Earth cooled down, most of the water vapour condensed and formed the oceans.
Decreasing Carbon Dioxide and increasing Oxygen
Earth cools and oceans form --> Forms of life evolve in the oceans and photosynthesis begins ---> Oxygen builds up in the Oceans. ---> Oxygen builds up in the atmosphere
Carbon dioxide is dissolved in the oceans ---> Marine organisms used the dissolved carbon dioxide to make calcium carbonate for shells ---> The shells of dead marine organisms fall to the sea bed and become part of the sediment ---> Over millions of years the layers of sediment become squashed and form sedimenary rocks.
- Early Earth probably had an atmosphere dominated by carbon dioxide similar to the atmosphere of Venus today.
- There are a group of one-celled organisms that can live in an oxygen free environment. These are the bacteria or prokaryotes. They do not have a nucleus and reproduce only by cell division. These creatures are the earliest evidence of life on earth. They were the first organisms to develop photosynthesis. Photosynthesis today is balanced by oxygen using respiration.
- Hypothesis: Oxygen was nearly absent in the atmosphere of early Earth so photosynthesis would have created a net gain of oxygen first in the ocean and later in the atmosphere. Eventually with sufficient oxygen in the atmosphere respiration would have balanced photosynthesis except when burial removed the organic material from the oxygenated water or air. Before…