Origins of Life and Human Evolution Timeline

Spallanzani and Spontaneous Generation

Lazzaro Spallanzani repeated Needham's experiment, but instead, he removed the air from the flask. No growth occurred, so he disproved the theory.

Louis Pasteur and Microorganisms

Louis Pasteur demonstrated that air is full of microorganisms by passing air through gun cotton filters. The filter trapped tiny particles floating in the air. By dissolving the cotton in a mixture of ether and alcohol, particles were released and then settled to the bottom of the liquid. It revealed numerous microbes that resembled various types of bacteria. He realized that if bacteria were present in the air, then they would likely land on and contaminate anything exposed to it.

Abiogenesis vs. Biogenesis

• Abiogenesis: The study of how life originally arose on the planet, together with the belief in the spontaneous generation of life from non-living matter.
• Biogenesis: The process in which life forms from similar life forms. It states that living things can only be produced by another living thing.

The Oparin-Haldane Theory

According to the Oparin-Haldane theory, life evolved in the oceans during a period of time when the atmosphere was reducing. Organic compounds were synthesized non-biologically by ultraviolet light energy which, in the absence of an ozone shield, would penetrate the upper layers of the ocean.

The Miller-Urey Experiment

Stanley Miller constructed an apparatus that recreated the early conditions of Earth. He circulated steam through a mixture of ammonia, methane, and hydrogen and then sent a high-energy electrical spark through the mixture in imitation of the hypothesized lightning bolt. He did this for a week, after which his mixture became red and murky and contained amino acids.

Timeline of Human Evolution

• Australopithecus afarensis: 5 million years ago. Walked upright. Brain size was 35% of a modern human's. Not proficient in using tools.
• Homo antecessor: 1.2 million years ago. Brain size around 1000 cm³.
• Australopithecus robustus: Massive flat or concave faces and small teeth. 1.5 million years ago.
• Homo habilis: Primitive stone tools and a brain size 50% of a modern human's. 2.5 million years ago.
• Homo ergaster: 2 million years ago. Small face and teeth.
• Homo erectus: 1 million years ago. Fairly modern human features.
• Homo neanderthalensis: 0.5 million years ago. Tools and social structures.