Answer to Question 1
Life could have originated on mineral surfaces near hydrothermal vents, where lots of prebiotic chemistry could have taken place. Alternatively, life could have originated on the surface as a result of a process similar to that occurring in the Urey-Miller experiment. The organic compounds from which life formed could have been produced within the atmosphere from UV irradiation or in lightning discharges. Alternatively, some complex prebiotic compounds may have been synthesized in interstellar dust clouds and brought to the Earth by interplanetary dust particles or by meteorites.
Answer to Question 2
Biologists use the polymerase chain reaction to determine the part of the DNA sequence used to encode ribosomal RNA (rRNA). With this information, they can determine the differences in the rRNA of varying organisms. The greater the difference between two organisms' rRNA sequence, the farther apart they are placed on the tree. After a number of genetically diverse organisms are analyzed in this way, the Universal Tree of Life can be created.
Micrographs of nerve cells taken with different types of light microscopes.
Ascomycetes Life Cycle
Types of Problems Used to Measure Intelligence
Types of Electrical Potentials in Biological Systems
The early stages of the human life cycle.
Half-life formula