What does it mean?  

The 'origin of life' essentially refers to the organism(s) and life that first arose on Earth, and became the ancestors for all life there is today. 

Oparin-Haldane Hypothesis and Miller-Urey Experiments: 

These two groups of people worked in the 1920s and 1950s, respectively, to discover the theory we now know as abiogenesis. Encyclopedia Britannica put it best when they said "Abiogenesis is the idea that life arose from nonlife more than 3.5 billion years ago on Earth. Abiogenesis proposes that the first life-forms generated were very simple and through a gradual process became increasingly complex." There are MANY different ideas as to where life arose, some say it could have come from below Earth's surface or hypothermal vents on the ocean floor. These two are the most probable considering the science behind it.  The 'primordial soup' theory suggests that life started in a pond or ocean after a combination of chemicals from the atmosphere and energy made amino acids. 

Why 'primordial soup' has been DISPROVED!:

This theory is based on the assumption that the amino acids could form real proteins through their first interaction, which is not possible. The most likely assumption for the origin of life today is deep sea vents or underwater hot springs. These vents could have initiated "simple metabolic reactions, ~ that enabled the leap from a non-living to a living world." (WHOI)

Important vocabulary: 

speciation: the process by which one species splits into two or more species. 

prezygotic barriers: 'BEFORE the zygote' it blocks fertilization from occurring.  

postzygotic barriers: 'AFTER' the zygote' may contribute to reproductive isolation after the hybrid zygote is formed. 

The Very Beginning ... 

• Earth formed 4.6 billion years ago
  
• Rock and ice prevented life
• The atmosphere was thick with water vapor (almost no free oxygen)
• When water vapor condensed for form oceans, early oceans consisted of organic molecules ("primitive soup")                 
• The beginning of life started with the abiotic synthesis of organic molecules. These cells joined together to form macromolecules. When these macromolecules joined, they form PROTOCELLS (a primitive cell: a cell with a membrane that maintains the different chemistry from its surroundings.) These primitive cells make inheritance possible. 
• Necessary conditions for PROTOCELLS to form were met in VESICLES: fluid-filled compartments bound by a membrane-like structure. 

FOSSIL RECORD

• RADIOMETRIC DATING: a means to determine the age of a fossil, considers the rate of decay of radioactive isotopes
• HALF-LIFE: how the rate of decay is determined, the period of time that it takes 50% of the substance to decay (each substance has a characteristic half-life) 

LIFE'S HISTORY: KEY EVENTS

• Evidence of first life on earth (3.5 billion years ago) comes from Stromalites: when prokaryotes bind sediment to make layered rocks
• "Oxygen Revolution"- when seas and lakes started to contain oxygen. 2.7 billion years ago, oxygen started evaporating into the atmosphere
• The first Eukaryotes can be explained by the ENDOSYMBIONT THEORY: chloroplasts and organelles were originally small single-cellular organisms that now live in larger cells
• CAMBRIAN EXPLOSION: a short period of time when most animals of the fossil record appeared
• Mankind emerges: Occurred after the extinction of dinosaurs. Has continued until today. 

SPECIATION AND EXTINCTION

BEGINNING OF INHERITANCE

• First genetic material was RNA
• RNA that can carry out enzyme-like functions: Ribozymes
• RNA could store in and pass along genetic information between protocells