Earth’s Mantle and Evolution of Life

Earth’s Mantle and Evolution of Life

The evolution of Earth is still not completely decoded. According to a study published in the journal ‘Nature Communications’, an evolution of the Mantle of the Earth could have not only controlled the evolution of the atmosphere, but also the evolution of life. Geological processes like separation of the supercontinents or changes in mantle dynamics might result in the appearance or extinction of the species.

Role of Earth’s Mantle:

The Earth possessed huge amounts of oxygen before 2.3 billion years ago, but this oxygen remained deep under the surface of its mantle. According to the study, although there were amounts of oxygen before the Great Oxidation Event (GOE), it could not concentrate in the atmosphere. This was because it existed as rocks until they were broken down by plate tectonics and recycled into the Earth's surface. Nowadays, oxygen exists at a ratio of 21 percent in our atmosphere and is essential for life on our planet.

It is due to the Earth's mantle and volcanic activity. The mantle's composition is rich in magnesium and iron, combined with silicates, which dissolve in iron. The resultant molten rock, called magma, is less dense than the Earth’s crust. As magma rises towards the Earth's surface, it cools and crystallizes to create lighter rock. When this magma solidifies, the weight of this rock compresses the crust. This constant formation of new crust results in slight crustal movements and shifts. This happens along tectonic plate boundaries on the Earth’s surface.

Once Earth had a magma ocean, the composition of Earth’s mantle was the same as the present-day one. The mantle was rich in iron and magnesium silicates, but it contained little silicon because they were converted to oxygen compounds during volcanism. Before that period, Earth’s mantle held abundant silicon in the form of bridging chlorites and low-crystal content quartz polymorphs.

About Great Oxidation Event:

The early Earth was devoid of oxygen. The atmosphere began changing during what is known as the Great Oxidation Event (GOE). This was a time where atmospheric oxygen began to build up in the Earth's atmosphere. This process of increased oxygenation happened gradually over hundreds of millions of years.

It refers to the great oxidation event which refers to a series of chemical changes that geologists and geochemists have observed in rocks that are between 2.5 and 2.3 billion years old. This period is called the eon where oxygen started to rapidly appear in our atmosphere, oceans, and rocks. The world as we know it today would not exist without this event because oxygen is needed for all animals and plants on Earth today.

The Great Oxidation Event was a rapid increase in atmospheric oxygen, which accelerated the rate of chemical weathering and removal of CO 2 from the atmosphere during the Proterozoic Era. These changes resulted from increased oxygen given off by ancient cyanobacteria (blue-green algae), which were preserved in rocks as structures called stromatolites. Oxygen first accumulated in Earth’s atmosphere at this time and has been present ever since.

About Earth’s Mantle

The mantle is mostly solid, but around the edges, it can flow like a liquid, albeit slowly. Solid lumps of mantle rock originate on Earth's surface and are carried down by subduction. There, they slowly drift back up through the mantle, riding conveyor belts of tectonic plates that move Earth's lithosphere (crust and uppermost mantle) around the planet.

Earth’s mantle is another of the layers that make up our globally unique planet. About 2,900 kilometers thick and making up 84 percent of Earth’s total volume, the mantle is the thickest layer in our planet. The mantle has a higher heat flow than the crust above it or the core below it. This means that the pressure on the mantle to melt is higher than any other part of the planet, as it should be since so much of Earth’s internal energy comes from radioactive decay in its hot core. The same radioactive decay also produces heat throughout Earth’s interior, melting much of its upper layers over time.

The upper part of the mantle below the lithosphere is called the asthenosphere. The word astheno means weak. It is considered to be extending up to 400 km. It is the main source of magma that finds its way to the surface during volcanic eruptions. Although it is easy for anything to melt in the asthenosphere compared to the lithosphere, rock fragments never actually melt completely, despite a high partial pressure of CO2 or water vapor in the upper mantle.

About Cyanobacteria

Cyanobacteria are the oldest known form of life on Earth, and they are one of the most successful. They have no specialized cells such as secretory or reproductive cells. Their bodies are like smooth sheets folded into very tight rolls. The pigment that gives them their color is like the chlorophyll in nearby plants that lets them turn sunlight into nutrients for themselves.

Cyanobacteria, also known as blue-green algae, appear simple at first glance: they are single-celled organisms that lack the specialized organs of other green organisms such as plants and true algae. They are more closely related to bacteria than to plants or fungi, and they have a high enough DNA likeness to animals for some species to be placed in the kingdom Animalia along with us. Cyanobacteria have the distinction of being the oldest known fossils, more than 3.5 billion years old.