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.
â Pen (girl) Pen [pen] as a name for girls (also used as boys' name Pen) is of Greek derivation, and the meaning of Pen is weaver. Pen is a version of Penelope (Greek): from pene. Associated with: greek. Pen has 5 relations via Penelope: Penina, Penna, Penney, Pennie and Pennyâ¼.