Earth Science: Fossil Dating and Endosymbiosis

Topic 3: The Origin & Evolution of Life

• Early Earth & Change Over Time (Sections 25.1-25.5; 21.4, 28.1) are covered
• Evolution is the change in populations of organisms across generations
• Evolution is a biological context

What is Evolution?

• Diagrams depicting evolutionary relationships and diverse organisms are included
• The diagram shows the interconnectedness of various species, highlighting common ancestry and branching patterns in the evolutionary tree.
• Various groups of organisms, such as amphibians, reptiles, birds, and mammals are shown in the diagram.

Evolution: Biological Context

• Evolution is a process of how populations of organisms change across generations
• Early amphibian Tiktaalik roseae is shown
• The evolution of terrestrial vertebrates is illustrated with a diagram displaying the transition from fish to land-dwelling organisms like amphibians, reptiles, mammals, and birds through time.
• Evidence like the amniotic egg, mammary glands, and hair are shown as evidence.

To understand evolution...

• The necessity to understand life's origins is emphasized
• Diagram illustrating the evolution of terrestrial vertebrates showcasing various evolutionary steps is included

What do we need to learn about…

• Key topics to understand evolution include: the origination of life, requirements for evolution, mechanisms of evolution, particularly natural selection
• The progression from Topic 3-6 is presented as a hierarchical learning structure
• Each topic builds upon the previous, enabling a comprehensive understanding of the evolutionary process.

Topic 3: Learning Objectives

• Students should be able to explain conditions on early Earth
• Understand important events leading to life on Earth, starting from the formation of organic molecules (including Miller-Urey Experiment & RNA World to DNA World)
• Explain the topics of the "Prokaryotic World," Endosymbiotic Theory, and Horizontal Transfer
• Apply and calculate fossil ages, utilizing both absolute and relative dating methods

So when did life originate?

• A timeline, showing the sequence of events from Earth's formation to various milestones in the development of life.
• The development stages include the formation of the Earth, first rocks, first microfossils, eukaryotes, multicellular fossils, skeletons to etc.
• The units are all measured in BYA (billion years ago)

We can translate Earth’s history…

• A table that converts Earth's history into a 24-hour scale. This table demonstrates the timing of major events in Earth's history.
• Each event is correlated to a specific time on the 24-hour clock

What has changed in the last ~4.5 billion years?

• Earth's position of rigid rock plates has changed, including the merging and separation of continents. A supercontinent Pangea (200 million years ago) formed is noted
• The planet's climate has gradually cooled
• Climate changes impact organisms' survival.

Characterizing the conditions of early earth (4.2-3.9 bya)

• Little free oxygen (O2) was present 4 billion years ago
• Early Earth’s atmosphere consisted primarily of hydrogen, carbon dioxide, nitrogen, and water and small amounts of ammonia, methane, carbon monoxide, and hydrogen sulfide
• The atmosphere was hotter than today
• The earliest microbes evolved in these environments and still inhabit similar conditions.

Given these changes in the environment, how did life originate?

• Scientific premise: All natural phenomena, including life, can be explained by the application of natural laws
• Life’s origin is explained in terms of chemistry.

Origination of life: what led to the formation of cells?

• Cell theory: Cells are the basic units of life
• Questions to understand the formation of cells:
  • Where do organic molecules come from?
  • How do cell membranes form?
  • How is the relationship established between DNA and Proteins?
  • How does cell metabolism get started?

Where do organic molecules come from?

• Inorganic molecules led to organic molecules (inorganic to organic)
• The Miller-Urey experiment proves that organic molecules can form spontaneously from inorganic molecules

Artificial Synthesis of Organic Molecules

• Transition from inorganic to organic molecules is demonstrated
• The 1828 synthesis of urea by Friedrich Wöhler from inorganic compounds is highlighted, revealing that organic compounds can be made from inorganic ones.

Miller-Urey Experiment – 1952

• Demonstrates that organic molecules, like amino acids, can form spontaneously under conditions believed to exist on early Earth.
• Simulated early Earth's atmosphere and conditions, particularly the absence of oxygen and the presence of energy input from sparks.

How Do Cell Membranes Form?

• Protocells: Early membranes naturally trapped organic molecules, creating life in a bubble. This led to the compartments necessary for life

Why are cell membranes important?

• Cells and organelles are surrounded by membranes
• Membranes comprise hydrophilic and hydrophobic components and are similar to the molecules that comprise membrane
• Membranes form spontaneously

How did cell membranes originate?

• Protocells formed spontaneously in the early Earth, trapping organic molecules within.

How is the relationship established between DNA and Proteins?

• The central dogma of molecular biology (DNA to RNA to protein) was presented
• The conversion of information flow from DNA to RNA to protein is the central dogma and a key process for life.
• RNA world hypothesis: The idea that RNA played a more central role in early life functions than DNA.

Prior to having DNA, RNA and proteins...

• The RNA world hypothesis is the idea that RNA played a central role in early life functions, before DNA and proteins
• Organic soup with proto cells
• Trillions of random RNA polymers
• RNA monomers duplicated themselves

From the RNA world to the central dogma

• During RNA replication, errors resulted in new RNA and molecules
• RNAs were linked with amino acids and formed proteins
• Proteins with greater enzymatic capabilities superseded RNA in function
• DNA became more stable than RNA, gradually taking over, while maintaining RNA's essential intermediary role

How does cell metabolism get started?

• Mutations and diversification, and complexity in proto cells lead to the development of proteins with specialized functions.
• Proteins bridged organic molecules entry into and out of cells, linked them for membrane and energy functions

Establishment of metabolism

Origination of life: what led to the formation of cells?

• Questions to understand cell formation:
  • Where do organic molecules come from?
  • How do cell membranes form?
  • How is the relationship established between DNA and Proteins?
  • How does cell metabolism get started?

Relative Dating

• Fossils are placed in a relative order of age (older to younger)
• This is often possible when fossils are found within sedimentary rocks.

Absolute Dating

• Applying numerical dates to fossil ages
• Radiometric dating uses the different half-lives of radioactive isotopes.

Types of Radiometric Dating Questions

• Determine fossil age using isotope masses and half-lives.
• Determine the number of half-lives based on percentages of parent and daughter isotopes.
• If fossil is a certain age, percentages of parent/daughter isotopes will be determined.

What is the correct order for the events…

• The correct sequence of events for early life is Formation of Organic Molecules, Formation of Membranes, RNA World to DNA transition, and Initiation of Metabolic Pathways

We have now covered the proximate explanations…

• The crucial diversification and adaptation of early life are touched on.

What have been some of the major events in the evolution…

• Major events in the evolution of life are described and include the origin of organic molecules, membranes, RNA to DNA transition and metabolism.
• The last universal common ancestor, the earliest organisms that evolved, and the prokaryotic cell concepts are highlighted

Back to the 24-hr scale

• A table presents major events in Earth's history, translated to a 24-hour period.

First life: Prokaryotes ~3.5 bya (5:20 am)

• Unicellular microorganisms that lack membranes
• Metabolically diverse

Stromatolites

• Mats formed by prokaryotic fossils and sediment
• Formed in layers within marshes and lagoons

Prokaryotic World

• Prokaryotes dominated for nearly 2 billion years
• First prokaryotes were probably oxygenic photosynthesis bacteria (e.g., cyanobacteria)

Origin of Eukaryotic Cells (2.5 bya; 10:40am)

• Prokaryotic DNA is not bound by a membrane
• Evolution of eukaryotes
• Transcription and translation are now possible

Endosymbiotic Theory

• Mitochondria and chloroplasts originated as mutualistic endosymbiotes
• Endosymbiotes lost ability to be independent entities, becoming organelles

Origin of multicellularity (1.2 bya; 5:36 pm)

• Multicellularity arose from daughter cells developing cell adhesion molecules and extracellular matrix
• Multicellularity led to specialization and increased complexity