Unit+7+Teacher+(Lesson+6)

Unit Overview

• Unit 7: Natural Selection

  • Lesson 1: Natural Selection

  • Lesson 2: Population Genetics

  • Lesson 3: Hardy Weinberg Equilibrium

  • Lesson 4: Evidence of Evolution & Common Ancestry

  • Lesson 5: Phylogeny

  • Lesson 6: Speciation & Extinction

  • Lesson 7: Origins of Life on Earth

Lesson 7: Origins of Life on Earth

• Aim: What scientific models explain the origin of life on Earth?

Topic 13: Origins of Life on Earth

• Learning Objective:

  • SYI-3E “Describe the scientific evidence that provides support for models of the origin of life on Earth.”

Disclaimer Statement

• No definitive knowledge of how life originated on Earth exists.

• Numerous well-supported hypotheses propose explanations for this phenomenon.

Evolution & Speciation

• Earth's Formation:

  • Earth formed approximately 4.6 billion years ago (bya).

• Early Earth Conditions:

  • Environment unsuitable for life until around 3.9 bya.

  • Earliest fossil evidence dates back to 3.5 bya, specifically of cyanobacteria.

How Did Life Arise?

• Early Earth contained inorganic molecules conducive to synthesizing organic molecules.

  • Free energy and abundant oxygen played crucial roles.

  • Organic molecules may have been delivered to Earth through meteorites or celestial events.

Early Atmosphere

• Early Earth was volcanic and hot with a minimal oxygen atmosphere, mainly composed of hydrogen sulfide and methane.

  • Initially not conducive for life.

• As Earth cooled, the atmosphere changed, yet remained unstable (characterized by storms and heat).

• Significant oxygen levels in the atmosphere emerged only after photosynthetic organisms evolved.

Experimental Data

• Hypothesis by Oparin and Haldane:

  • Early Earth was composed of hydrogen, methane, ammonia, and water.

• Miller and Urey Experiment:

  • Tested Oparin and Haldane’s hypothesis in a lab setting.

  • Resulted in the production of organic compounds and amino acids.

Building Blocks of Life

• Miller and Urey’s findings supported the concept that the organic molecules formed were fundamental building blocks for macromolecules.

From Simple To Complex

• Simple organic monomers from primordial soup likely polymerized into complex molecules under early Earth conditions.

• Formation of complex molecules capable of replication and information storage, such as RNA, occurred.

• This marked the emergence of a common ancestor for all species.

RNA World Hypothesis

• Proposition: Early Earth had conditions favorable for RNA formation.

• RNA’s dual role as an enzyme and self-replicating molecule suggests it was the original form of genetic material.

• DNA later became the dominant information storage molecule due to its increased stability compared to RNA.

Review

• Reflect on the endosymbiont theory's relevance to the origins of life discussion.