Compressional or P (for primary)
, Transverse or S (for secondary)
, Love, and Rayleigh. Primary waves push and pull the ground in the direction the wave is traveling. Secondary waves travel in the same direction, but they shake the ground back and forth perpendicular to the direction the wave is traveling. Love waves move back and forth horizontally. Rayleigh waves cause both vertical and horizontal ground motion.
What does Earth have that other planets don't, the basis of life? Water, of course.
Humans and other mammals drink specifically <em>freshwater</em> though, which is far more precious and less abundant than saltwater.
The correct answer is - cyanobacteria.
The atmospheric oxygen came from the cyanobacteria. These were one of the earliest living organisms on Earth. The cyanobacteria was using photosynthesis in order to create its own food. The photosynthesis process requires sunlight, carbon dioxide, water, and oxygen. The oxygen is mostly released as a waste product from the process of photosynthesis, thus the cyanobacteria were literally releasing oxygen that was ending up into the atmosphere. As more and more cyanobacteria there were across the planet, more and more oxygen they were releasing into the atmosphere, slowly changing the composition of the atmosphere, and setting the basis of it as we know it now.
