Analysis of air bubbles trapped in fossils, such as in fossil amber, show that our air in earliest times contained about 35% oxygen. Today, the average oxygen content of our air is approximately 20%. In some larger, more polluted cities, oxygen content in the air has been measured at 12 - 15%.
There are 297 words which start with 'pen'. 3 letter words starting with 'pen': pen. 4 letter words starting with 'pen': pend. pens.
uk â /ËÉÊ.pÉn ËmaÉªnd/ us â /ËoÊ.pÉn ËmaÉªnd/. have/keep an open mind. B2 to wait until you know all the facts before forming an opinion or making a judgment: We should keep an open mind until all of the evidence is available. Thesaurus: synonyms and related words. Open-minded. broad-minded. enlightened. freethinker.