Start chest compressions. (Initiate Cardiopulmonary resuscitation.)
Defibrillation stops ventricular fibrillation an resumes normal heart rhythm by delivering electric shock to the chest. Cardiopulmonary resuscitation delays heart damage after patient's collapse. Both are a must within the first few minutes after cardiac arrest to maximize chance of survival.
Comparing and contrasting a compound light microscope, basically both operate by bouncing tiny particles or waves off of objects in order to make them visible. Electrons are smaller than light photons so we can see smaller objects clearly with electron microscopes. There are disadvantages though. First, color is a function of light wave frequency so we can't see electron micrographs in color. Color can be added artificially though by computer to differentiate structures, (think photoshop). Also, we cannot see electrons so we make them visible by bouncing them off a cathode ray screen similar to a TV set or computer monitor
Water, air, food, shelter
The correct answer is Oxygen.
The surface of the Earth was liquefied. As the Earth cooled, an atmosphere generated primarily from gases erupted from volcanoes. It constituted methane, hydrogen sulfide, and ten to 200 times as much as carbon dioxide in comparison to today's atmosphere.
It was considered that there was an extreme volcanic activity for the initial billion years of the existence of the Earth. The initial atmosphere was possibly majority carbon dioxide will no or little concentration of oxygen. There were slight quantities of ammonia, water vapor, and methane.