Earth’s Early History

Mystery of Life’s Origins Using radiometric dating, scientists believe the Earth to be between 4.2 and 4.6 Billion Years Old. Earth’s early atmosphere contained little or no oxygen. Made up of mostly: CO2, water vapor, and nitrogen

How did Life Begin? 3 ideas of how life may have gotten on Earth Divine Creation – a higher being put us here on Earth Extraterrestrial Origin – life may have come to Earth via an asteroid or meteorite. Spontaneous Origin – process through which life is thought to have developed when molecules of non-living matter reacted chemically during the 1st billion years.

Spontaneous Origin 1920’s A.I. Oparin – Primordial Soup Model Oceans were a big soup bowl with large amounts of organic molecules Chemical reactions spontaneously occurred in soup with energy from lightning/volcanoes Proposed that Earth’s early atmosphere lacked oxygen, yet had plenty of nitrogen, hydrogen, water vapor (earth was hot), methane and ammonia.

Stanley Miller 1953, tested Oparin’s hypothesis Placed gases in apparatus, zapped it, and found some basic chemicals could have formed spontaneously 2 problems Too slow Not sure methane and ammonia was available, and if it was, UV would destroy it

Louis Lerman 1986 – Bubble Model Chemical reactions took place in the bubbles of the ocean Reactions would take place faster in bubbles Inside bubbles, methane and ammonia protected from UV rays Leading hypothesis accepted to date

Origins of Eukaryotic Cells Endosymbiotic Theory – proposes that a symbiotic relationship evolved over time, between primitive eukaryotic cells and the prokaryotic cells within them. Ex. Mitochondria and Chloroplasts are thought to have been ancient prokaryotes Both have their own DNA, ribosomes and both reproduce by binary fission like bacteria cells