Choose the incorrect statements about the conditions on early earth from the following:
A. There was no atmosphere on early earth.
B. The UV rays from the sun broke up water into hydrogen and oxygen, and the lighter O2 escaped.
C. Oxygen combined with ammonia and methane to form water, CO2 and others.
D. Water vapour, methane, carbon dioxide and oxygen released from the molten mass covered the surface of early earth.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → B and D only
Earth formed about 4.5 billion years ago with no atmosphere. Gases from the molten mass covered its surface, UV rays split water, and the gases reacted further before the ozone layer formed. The two changed words to watch here are the gas that escaped and the gas that was released.
A. There was no atmosphere on early earth. — True. This is how NCERT begins the account of early earth.
B. The UV rays from the sun broke up water into hydrogen and oxygen, and the lighter O2 escaped. — False. Hydrogen is the lighter of the two gases, so it was H2 that escaped. The oxygen stayed back and reacted with other gases.
C. Oxygen combined with ammonia and methane to form water, CO2 and others. — True. The oxygen left behind after the escape of hydrogen combined with these gases.
D. Water vapour, methane, carbon dioxide and oxygen released from the molten mass covered the surface of early earth. — False. The fourth gas was ammonia, not oxygen. Free oxygen came later, from the splitting of water by UV rays.
NCERT Extract:
Origin of Life – “… In the solar system of the milky way galaxy, earth was supposed to have been formed about 4.5 billion years back. There was no atmosphere on early earth. Water vapour, methane, carbondioxide and ammonia released from molten mass covered the surface. The UV rays from the sun brokeup water into Hydrogen and Oxygen and the lighter H2 escaped. Oxygen combined with ammonia and methane to form water, CO2 and others. The ozone layer was formed.”