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.
Quick Summary. The Latin root word pend and its variant pens both mean âhangâ or âweigh.â These roots are the word origin of many English vocabulary words, including pend, pendant, suspense, and expensive. An easy way to remember these different meanings is that a pendant âhangsâ from your neck, whereas you have to âweighâ out a lot of money if something is expensive.