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.
We also have lists of Words that end with Phil, and words that start with Phil. Search for words that start with a letter or word: 11 Letter words that contain Phil. 1  Acidophiles. 2  Acidophilic. 3  Ailurophile. 4  Amphiphiles. 5  Amphiphilic.