UNIT 6: Evolution and Classification Chapter 12.3 - 12.4 The History of Life

Ch. 12.3 Origin of Life Earth was different billions of years ago The Earth is ~4 billion years (by) old. We know this because radiometric dating can establish the age of elements (carbon, uranium, potassium, argon, etc.) The oldest known rocks have been here ~4 by. Scientists infer organic molecules began to accumulate at the same time.

Ch. 12.3 Origin of Life First Organic Compounds So how and where did elements assemble into organic compounds and form life? In the 1920s Oparin hypothesized that organic molecules in the atmosphere & high temperatures formed amino acids and proteins… but he never tested his idea.

Ch. 12.3 Origin of Life Miller-Urey Experiment Conducted in 1953 using Oparin’s hypothesis as a starting point. Miller & Urey built an apparatus that simulated the atmosphere of early Earth. Electric sparks were added to substitute lightning and catalyze chemical reactions. This has been repeated and continues to produce organic molecules; it supports Oparin’s hypothesis.

Ch. 12.3 Origin of Life Did They Come From Outer Space? Many scientists hypothesize that the organic compounds may have come from space. Fallen meteorites may have brought organic compounds to Earth. “Panspermia Theory” Or the Ocean? Others hypothesize these compounds formed deep in the ocean near hydrothermal vents.

Ch. 12.3 Origin of Life Panspermia Theory Hydrothermal Vent

Ch. 12.4 Early Single-Celled Organisms Eukaryotic cells may have evolved through endosymbiosis Endosymbiosis is a theory that is supported by a large body of evidence. It proposes that ~2-1.5 bya a small aerobic prokaryote was engulfed by and began to live & reproduce inside a larger, anaerobic prokaryote. Eukaryotic cells differ from prokaryotic cells in many ways. Larger DNA is organized into chromosomes in a nucleus Contain membrane-bound organelles.