Question

what was the percentage of Co2 in air during pre-industrial revolution on the earth​

Answer 1

Carbon dioxide in Earth's troposphere

2011 carbon dioxide mole fraction in the troposphere
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Carbon dioxide (CO
2) is an important trace gas in Earth's atmosphere. It is an integral part of the carbon cycle, a biogeochemical cycle in which carbon is exchanged between the Earth's oceans, soil, rocks and the biosphere. Plants and other photoautotrophs use solar energy to produce carbohydrate from atmospheric carbon dioxide and water by photosynthesis. Almost all other organisms depend on carbohydrate derived from photosynthesis as their primary source of energy and carbon compounds. CO
2 absorbs and emits infrared radiation at wavelengths of 4.26 μm (asymmetric stretching vibrational mode) and 14.99 μm (bending vibrational mode) and consequently is a greenhouse gas that plays a significant role in influencing Earth's surface temperature through the greenhouse effect.[1]

Concentrations of CO
2 in the atmosphere were as high as 4,000 parts per million (ppm, on a molar basis) during the Cambrian period about 500 million years ago to as low as 180 ppm during the Quaternary glaciation of the last two million years.[2] Reconstructed temperature records for the last 420 million years indicate that atmospheric CO
2 concentrations peaked at ~2000 ppm during the Devonian (∼400 Myrs ago) period, and again in the Triassic (220–200 Myrs ago) period. Global annual mean CO
2 concentration has increased by more than 45% since the start of the Industrial Revolution, from 280 ppm during the 10,000 years up to the mid-18th century[2] to 415 ppm as of May 2019.[3][4] The present concentration is the highest for 14 million years.[5] The increase has been attributed to human activity, particularly deforestation and the burning of fossil fuels.[6] This increase of CO
2 and other long-lived greenhouse gases in Earth's atmosphere has produced the current episode of global warming. Between 30% and 40% of the CO
2 released by humans into the atmosphere dissolves into the oceans,[7][8] wherein it forms carbonic acid and effects changes in the oceanic pH balance.