Specialty Medical Coding Certification. 1  Hematology and Oncology â CHONCâ¢. 2  Internal Medicine â CIMCâ¢. 3  Interventional Radiology and Cardiovascular â CIRCCÂ®. 4  Obstetrics Gynecology â COBGCâ¢. 5  Ophthalmology â COPCâ¢. 6  Orthopaedic Surgery â COSCâ¢. 7  Otolaryngology â CENTCâ¢. 8  Pediatrics â CPEDCâ¢. FREE Practice Exam & Study Guide through Aug 31st.
Oxygen is a chemical element with symbol O and atomic number 8. It is a member of the chalcogen group on the periodic table and is a highly reactive nonmetallic element and oxidizing agent that readily forms compounds (notably oxides) with most elements. Photosynthesis releases oxygen, and respiration consumes oxygen.
The modern-day organisms that seem oldest, in an evolutionary sense, are microbes that. live in the hot water around volcanic vents on the ocean floor. Nearly all of the oxygen in the Earth's atmosphere was originally produced by photosynthesis in the leaves of trees that covered the continents 3.5 billion years ago. The requirement of liquid water is the most severe constraint on the development of life.