Another Miracle in the Air
The concentration of oxygen in the air is about 21%.
But if it is reduced to 18%, some person may have a headache. If it is reduced to 12%, most person feel faint and nauseous. If the concentration of oxygen in the air is decreased to 10%, people will lose consciousness. At 8%, people will die in 6 to 8 minutes. At 6%, people will die in 6 minutes.
But if concentration of oxygen in the air is higher or 60% or more, oxygen will damage the human body. So, in the medical care, oxygen at 50% concentration is provided for a patient who needs more oxygen only for 48 hours; 100% concentration oxygen only for 6 hours.
If the concentration of oxygen in the air is 35% or more, forests would break into spontaneous flames.
When living things invaded into the land from the sea 4.2 billion years ago, the oxygen concentration in the air was 10 to 14%. In Carboniferous period 300 million years ago when fern was prevailing, it was 30 to 35%. In 190 million years ago when dinosaurs got dominant, it was 15 to 22%. Today, we live in the air with 21% Oxygen concentration.
However, it is unknown why it is now 21%. And though it seems that the oxygen concentration in the air on the earth has been between 13% to 35% throughout the history of the earth, the reason why the oxygen level has been kept in the range is unknown.
So, if any other planets in the universe have physical conditions suitable for emergence of living things and evolution of life to higher forms of life, there is no assurance that they can have suitable concentration of oxygen for man-like living things.
So, by chance, the oxygen concentration in the air on the earth has been suitable for evolution of living things to the human species.
This is another miracle that tells intervention of God to the nature on the earth for the purpose of creation of the mankind.
It is a miracle, since we cannot scientifically explain why the oxygen concentration today is about 21%, so suitable for human beings.
O2 build-up in the Earth's atmosphere. Red and green lines represent the range of the estimates while time is measured in billions of years ago (Ga).
Stage 1 (3.85–2.45 Ga): Practically no O2 in the atmosphere.
Stage 2 (2.45–1.85 Ga): O2 produced, but absorbed in oceans & seabed rock.
Stage 3 (1.85–0.85 Ga): O2 starts to gas out of the oceans, but is absorbed by land surfaces and formation of ozone layer.
Stages 4 & 5 (0.85 Ga–present): O2 sinks filled, the gas accumulates.
https://en.wikipedia.org/wiki/Geological_history_of_oxygen
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Act 4:26 The kings of the earth stood up, and the rulers were gathered together against the Lord, and against his Christ.
Act 4:27 For of a truth against thy holy child Jesus, whom thou hast anointed, both Herod, and Pontius Pilate, with the Gentiles, and the people of Israel, were gathered together,
Act 4:28 For to do whatsoever thy hand and thy counsel determined before to be done.
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Act 4:26 The kings of the earth stood up, and the rulers were gathered together against the Lord, and against his Christ.
Act 4:27 For of a truth against thy holy child Jesus, whom thou hast anointed, both Herod, and Pontius Pilate, with the Gentiles, and the people of Israel, were gathered together,
Act 4:28 For to do whatsoever thy hand and thy counsel determined before to be done.