Biology Chapter 14 - The History of Life

Early Earth and Atmosphere

• Earth formed approximately 4.6 billion years ago and was molten for around 500 million years before solidifying into a crust.
• The early atmosphere contained many greenhouse and poisonous gases, with little to no free oxygen.

Evidence of Early Life

• Clues indicating early life on Earth are preserved in rock formations.
• The earliest evidence of life dates back to about 3.5 billion years ago.

Fossils and Their Types

• Fossils are any preserved evidence of ancient organisms, while trace fossils serve as indirect evidence.
• Molds are impressions left by organisms, and casts form when these molds are filled with sediment.
• Replacement fossils arise when minerals replace the original organic material.
• Petrified specimens showcase mineral deposits within empty pores.
• Amber is hardened tree sap that can trap and preserve organisms.
• Original material preservation occurs through processes like freezing or mummification.

Paleontology and Fossil Formation

• Paleontologists are scientists who specialize in studying fossils and ancient life.
• Fossils are typically formed in sedimentary rock, not in igneous or metamorphic types.
• The fossilization process involves an organism's burial in sediment, layer building, mineral replacement, and eventual erosion revealing the fossil.

Dating Fossils

• Fossils must be dated to interpret ancient environmental patterns.
• Relative dating assesses age relations between rock layers, adhering to the law of superposition—where younger layers lie atop older layers.
• Radiometric dating, an absolute dating method, utilizes radioisotope decay to determine precise ages.
• The half-life of an isotope is the time required for half of its sample to decay.

Geologic Time Scale

• Earth's history is charted on the geologic time scale, divided into eons, eras, periods, and epochs, with Precambrian Time covering the first 4 billion years.
• During Precambrian Time, Earth formed, prokaryotic life emerged, and oxygen-producing bacteria contributed to the atmosphere.

Major Eons and Eras

• The Phanerozoic Eon marks significant life diversification.
• The Paleozoic Era includes diverse periods such as the Cambrian, characterized by a major life diversification known as the Cambrian explosion.
• The end of the Permian Period is noted for the largest mass extinction event.
• The Mesozoic Era is distinguished by dinosaur dominance and the breakup of Pangaea, concluding with a mass extinction caused by a bolide impact.
• The Cenozoic Era features diversification of mammals, birds, and flowering plants, with modern humans appearing in the Pleistocene and forming civilizations in the Holocene.

Theories of Life's Origin

• Spontaneous generation proposed that nonliving materials could produce life, later disproven by Francesco Redi's meat experiment.
• The theory of biogenesis states that living organisms produce other living organisms, validated by Pasteur's broth experiment.

Formation of Organic Molecules and Cells

• Simple organic molecules, such as amino acids, are believed to form from water, methane, ammonia, and hydrogen, energized by lightning and UV radiation.
• Proteins potentially formed with the assistance of clay particles, which helped bind amino acids together.
• Early cells enclosed their metabolic machinery in lipid membranes, with the first cells being prokaryotes.

Development of Eukaryotic Cells

• Eukaryotic cells are thought to have emerged around 1.8 billion years ago.
• The endosymbiont hypothesis suggests that mitochondria and chloroplasts originated from prokaryotes that lived within larger eukaryotic cells.
• Evidence supporting this hypothesis includes the presence of independent DNA in mitochondria and chloroplasts, their double membranes, similar sizes to prokaryotes, and reproductive methods resembling prokaryotes.