Photosynthesis is one of the most heavily discussed topics in biology courses. Probably a reason why they are regarded as such an important topic is because they have impacted Earth’s atmosphere in the course of centuries if not thousands of years. Today we will take a look at how photosynthesis altered Earth’s atmosphere for millions of years.
The first photosynthetic organisms appeared on Earth around 2700 million years ago (mya). Several hundred years later, other organisms such as unicellular algae and primitive plants arrived. Thus the earliest photosynthetic organisms contributed largely to atmospheric oxygen content during the early years of Earth.
Over the last 3.5 billion years, oxygen concentration of Earth rose. The oxygen produced from plants were used in oxidation of minerals and ended up in rocks and sediments. About 2100 mya, eukaryotes appeared, allowing oxygen concentration to increase through contributions from algae and other marine organisms. When the oceans and deposits were saturated with oxygen, oxygen began to build up in the atmosphere. And 300 mya, when multicellular organisms evolved, Earth’s oxygen levels had a peak of around 30kPa.
Chromatography
What is chromatography? It is a technique used to separate mixtures of substances based on their movement by capillary action on a piece of paper. There are two parts of the separation process: a mobile phase and a stationary phase. To take paper chromatography as an example, the solvent that develops the chromatogram is the mobile phase while the paper is the stationary phase.
When paper chromatography is used on a leaf, its several different pigments – xanthophyll, beta-carotene, and chlorophyll – are separated. First, the pigment is extracted from the leaf through a solvent that dissolves plant pigments. Then the extract is placed on chromatography paper and transferred to a chromatography solvent in a container. A chromatogram is formed when pigments separate and move at different speeds on paper.
Retention factor refers to the ratio of the distance a pigment moves to the distance solvent moves. It can be easily calculated by dividing the distance travelled by sample by the distance travelled by solvent. When the retention factor is compared to known retention factors of plant pigments, the pigments can be identified.
A similar type of paper chromatography is thin layer chromatography. Yet one difference is that the stationary phase is silica gel, cellulose, or aluminum oxide, not paper. One benefit that this type of chromatography brings is that it produces better, clearer results.
Works Cited
“Paper Chromatography.” Wikipedia, Wikimedia Foundation, 9 July 2019, en.wikipedia.org/wiki/Paper_chromatography.
“Geological History of Oxygen.” Wikipedia, Wikimedia Foundation, 12 July 2019, en.wikipedia.org/wiki/Geological_history_of_oxygen.
The Science Herald 
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