Earth’s atmosphere – From a hot cloud of dust and gas to life nurturing environment

 

The early atmosphere –

History of earth – 4.6 billion years. 

Evidences - Oldest occurring rock – Faux Amphibolites of the Nuvvuagittuq greenstone belt - found in Quebec Canada with age of 4.28 billion years. Isotopic analysis of meteorites, soil, rock samples of moon.

Faux Ambibolites (Nuvvuagittuq Greenstone Belt, Eoarchean, 4.28 Ga; western Ungava Peninsula, eastern side of Hudson Bay, Quebec, Canada) James St. John, CC BY 2.0 <https://creativecommons.org/licenses/by/2.0>, via Wikimedia Commons

 The continuous collisions between primordial solar nebula particles (interstellar gas and dust) is mainly considered responsible for the most rudimentary form of earth. This continued for some 150 million years until eventually clumped into a rock form. The mass of earth had very high temperature due to terrestrial accretion heat generated through –

o   Decay of radioactive isotopes

o   Gravitational energy of sinking metals

o   Impact of small planetary bodies bombarding into earth.

 ·         Eventually, rock material started melting bringing about sinking of heavier material rich in iron and nickel, to core and rising of lighter elements to top. The maximum amount of lighter primordial gases like hydrogen and helium escaped during this phase.

 ·      The light molten material crystallized to build initial thin crust. This thin and unstable crust collapsed again formed many times to ultimately form a thicker crust as a result of large scale convection current inside earth. At the same time, outgassing of gases from surface volcanic activity led to oceanic evolution and secondary atmosphere.

Oceanic evolution -

H2O particles were already present in the Earth mass during the planetary accretion phase of formation of earth. During outgassing temporary steam atmosphere was created which precipitated during the subsequent cooling phases of the earth.

Secondary atmosphere –

·         Volcanism was the major route through which degassing of volatile material from the inner Earth took place. Volcanic activity produces water vapor, Carbon dioxide, Carbon monoxide methane gas, nitrogen in substantial quantities but no oxygen.

Decrease in CO2 –

·         Carbon dioxide was the main gas providing heat in the early atmosphere as the early solar system was illuminated by a weak, young Sun that only delivered ∼75% of the present day energy.

According to a climate model, at 2.75 Ga, CO2 level was 500 times present atmospheric levels. However, by the Cambrian, CO2 levels were close to present atmospheric levels.

The main reason for the extraction of CO2 out of the atmosphere was the development of life forms in the ocean that seized carbon in organic and later inorganic (calcium carbonate) forms and buried it in sedimentary formations on the sea floor.

Evidence -  presence of early carbonated sediments,

        Increase in O2 –

·         The secondary atmosphere formed by outgassing was anoxygenic. Amount of oxygen in the atmosphere increased gradually through

• Solar radiation - UV rays break H2O into hydrogen and oxygen
• Organic photosynthesis by earliest form of life - Blue-green algae (Cyanobacteria) uses CO2 and H2O for photosynthesis and release free oxygen.

 ·         Oxygen production continued for 2.2 billion years and did not achieve considerable levels until 2 Ga and only approached present-day levels by 1.5 Ga. Due to chemical action with the material deposited through lava eruptions, such as iron and evaporite formations.

Evidence - Iron rock formation in earliest sediments at Isua in western Greenland aged 3.8 billion years ago. Barite gypsum bearing evaporite found in Pilbara region of western Australia. 3.5 billion years ago.

·         O2 level rose in atmosphere occurred with decrease in the iron deposition.

Evidence – Earliest form of life i.e. Eukaryotes which were present 1.4 billion years ago, require O2 content of about 0.02 present atmospheric level. Similarly, soft life forms like jelly fish, worms developed about 650 million years ago, which require the minimum oxygen level of 0.1 present atmospheric level. Plants first appeared 400 million years ago.

·         The evolution of more complex form of plants and animals extract more CO2 from the atmosphere and provide an additional source of O2.

·         Once O2 started to accumulate in the atmosphere, the production of ozone (O3) could occur, shielding the Earth’s surface from ultra violet (UV) radiation. 

 References –

• Neil C. Wells - The atmosphere and ocean: a physical introduction, 3rd Edition, Wiley Blackwell
• Essentials of Meteorology – An Invitation to the Atmosphere, Eighth Edition 2018, C. Donald Ahrens and Robert Henson, Cengage Learning.
• Brian Frederick Windley (2016) Geologic history of Earth, Encyclopædia Britannica. Available at https://www.britannica.com/science/geologic-history-of-Earth.  Accessed on November 23, 2020

 

 

 

River of ice

Lambert - Fisher Glacier, Antarctica. Image from Google earth

 

 

Glacier is a moving mass of ice. It is different to iceberg in that, it moves over land and is much larger in size. The term “glacier” is from the French word ‘glace’, which has been taken from latin word ‘glacies’, both meaning ice.

Glaciers are formed due to snow fall and accumulation of ice over longer periods of time. With increasing snowfall, ice accumulates in glaciers. This leads to two different processes in a glacier formation. First is the process of compression within the glacier. It makes the glacier much denser and heavier. Secondly, increased weight of the glacier makes it move downwards, towards a lower area.

While moving down, glaciers erode and deposit, thus creating many features. Antarctica, Greenland, Alaska, Himalayas are some of the regions with glaciated landscapes.

Why are glaciers relevant?

Though, the relevance of a glacier may be mainly as a vacation spot for people not living in its vicinity. Glaciers are much more than that. It is relevant to human life economically, environmentally as well as socially.

It is very difficult to assess the tangible economic value of a glacier for a nation or state. But it a priceless resource with immense direct and indirect values. Its importance can be analysed from a 2014 report by U.S. Geological Survey economists Catherine Cullinane Thomas and Christopher Huber and National Park Service economist Lynne Koontz. The report is about the economic gains from Glacier national park in 2014. The report shows the one year benefits received from the glacier park to the economy, in form of income and the employment generated in the area. This study is not only the single example of the economic relevance of a glacier. In reality, there are immense benefits and gains which are still not explored.

Environmentally, glaciers provide nutrients to soils, rivers, lakes and oceans. They are a great source of fresh water and has an important role in maintaining the water balance in climate. They are also important in maintaining the salinity level of the oceans. Infact, if we realise, glaciers are a relevant part of the whole environmental balance of nature. A minor change in this natural equilibrium may disrupt the whole system.

Khumbu Glacier- Highest glacier in the world. Image from Google Earth

 

Glaciers are relevant socially as well as culturally. They are sites of powerful sacred and symbolic meanings for local communities (Allison 2015). A study by Allison (2015) shows the spiritual connection of the communities in the Peruvian Andes, the Nepalese Himalaya, and the Meili Snow Mountains of Yunnan, China to the glaciers. Glaciers are source of many important rivers which are considered sacred by its masses.

Some Facts about Glaciers -

Largest glacier in the world - Lambert-Fisher Glacier in Antarctica, 400 km long, and up to 100 km wide.

Highest glacier in the world - The Khumbu glacier in north-eastern Nepal. Its elevation is 4,900 m at its terminus to 7,600 m at its source.

Oldest glacier – The oldest glaciers ice can be found in Antarctica which is about 1,000,000 years old. In Greenland it is more than 100,000 years old.

References –

Allison, Elizabeth. (2015). The spiritual significance of glaciers in an age of climate change. Wiley Interdisciplinary Reviews: Climate Change. 6. 10.1002/wcc.354.