Lesson 1.03

Earth's Early Atmosphere

Lesson 1.03 - Earth’s Early Atmosphere

Before we begin:

Remember, our curriculum (and state EOC) information is based off current Scientific Theories; possible explanations based on accepted evidence and experimentation.

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No one will ever know for certain how life began.

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If you have a different belief, that is 100% alright; we are not here to discuss what we each think is true. You do not need to believe what is taught in this course. However, you should be able to explain what the theories state when asked.

What makes Earth a �suitable home for life?

What makes Earth a �suitable home for life?

it has liquid water

an optimal distance �from the sun

an atmosphere that contains a mix of important elements and molecules

Before we dive in…let’s review Lesson 1.01!

What is the purpose

of a Scientific Theory?

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Before we dive in…let’s review Lesson 1.01!

What is the purpose of a Scientific Theory?

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to explain observed phenomena

a broad explanation for events that is widely accepted as true

Never become laws; based on strong scientific support; may change based on evidence

Objectives

• describe the conditions on Earth billions of years ago

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• summarize theories of how life began on Earth

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• describe the relationship between organic

compounds, nucleotides, RNA, and a universal

genetic code

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• explain the connection between the beginning of life and the universal genetic code of almost all organisms

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The fossil record and other clues help scientists study the history and origins of life on Earth. There are several theories and hypotheses about the origin of life on Earth, each based on supporting evidence from many different fields of science. By putting these ideas together, we can create a possible explanation on how life began on Earth.

1: Organic Molecules

2: RNA (Organic Macromolecule)

3: Microspheres

4: Prokaryotic Cells

Origin of Life on Earth

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Ancient Earth

Earth is 4.2 billion years old

This is calculated by radioactive dating of the moon rocks

The Earth was too hostile for life for over a billion years 🡪

molten and being impacted by meteorites (heavy bombardment)

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Water on Earth

Life depends on water, and we need it for the origin of life! How did it get here?

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During the Late Heavy Bombardment 4 bya, countless meteors rained down on the Earth

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Over time, these icy asteroids and comets delivered water and possibly organic compounds, such as amino acids.

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Water delivery, as well as possible organic compounds.

The Origin of Life

• Scientists believe the origin of life occurred around 3.8 billion years ago, after the planet had cooled & stabilized
• Where on Earth did it occur?

Hydrothermal Vent Hypothesis– still warm and nutrient-rich, but also protected from damaging UV radiation in the deep sea

Primordial Soup Hypothesis – the origin of life occurred in a warm little pond like a hot spring

One of the greatest scientific questions is HOW it occurred...

Chemical Evolution

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• A form of natural abiogenesis – the creation of life from non-living materials
• The origin of life occurred not in a singular event (like spontaneous generation), but by inorganic chemicals joining, reforming and becoming larger and more complex over time 🡪 eventually giving rise to the first cell.

Organic Molecules - How did the first ones appear?

• Many theories on how organic molecules found the energy to form…
• Oparin and Haldane (independently) proposed (1920s):
• Conditions of early Earth made it possible for chemical reactions to build small organic molecules from inorganic molecules in the atmosphere. The limited amount of oxygen, as well as the large amounts of energy provided by UV radiation and lightning, were thought to allow these reactions to occur spontaneously.
• Oparin and Haldane said that the reason we do not observe these reactions occurring today is that the atmosphere now has a greater amount of oxygen gas.
• Oxygen interferes with the reactions that would form carbon-based organic molecules

N₂

CH₃

CO₂

H₂

Reactants

(inorganic)

Products

(organic)

The primitive atmosphere contained inorganic gases spewing from volcanoes and hydrothermal vents (what gas is missing?!)

With the help of catalysts (lightening, heat, pressure, UV light), these inorganic gases would undergo chemical reactions to from organic building blocks of life

Sugars

Fatty Acids

Amino Acids

Nucleotides

Catalyst

Miller-Urey Experiment (1950’s)

• Purpose: to test the hypothesis of chemical evolution/Primordial Soup Hypothesis
• Set-up: used a closed system of tubes to simulate the primitive atmosphere
• Inorganic gases + Water + Heat + Electricity
• Findings: Simple organic molecules including amino acids had been produced

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N₂

CH₃

CO₂

H₂

The Other “Steps”

• Miller & Urey did not create life, they proved that the first “step” in chemical evolution is possible in a short time frame
• Monomers polymerized and aggregated over millions of years to form a cell
• Ex. Fatty acids form phospholipid bilayers when placed into water 🡪 cell membrane
• RNA can act as a protein and a molecule of heredity 🡪 replication & inheritance
• RNA World Hypothesis: RNA existed before DNA

• RNA World Hypothesis- Some scientists hypothesize that some of the first large organic molecules to form and self-replicate were RNA molecules, with DNA molecules forming much later.
• RNA can self catalyze
• These early RNA molecules would have contained the codes for building specific protein molecules from the amino acids present on Earth at that time.
• In order to gather evidence that this hypothesis is valid, we would need:
• A simulation of early Earth

conditions and long-term

study of the resulting

molecule

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• Microspheres- tiny bubbles filled with groups of large organic molecules; they can form under very specific conditions
• are not cells, but they do share some characteristics with cells.
• make it possible for the conditions in the interior to be different from the conditions outside (like a cell)
• Expand by absorbing additional molecules until they reach an unstable size, and then they split into smaller microspheres.

PROBLEM: Not true reproduction or cell division, but it may be a precursor to it.

• Microspheres
• The hypothesis of microspheres builds off of the RNA world hypothesis.
• If RNA molecules could self-replicate, it would mean that whenever a microsphere split, the early genetic coding in the RNA would pass to the newly formed microspheres.
• This could be a predecessor to how cells pass on their genetic information today and may help explain why all organisms share a universal genetic code.

First Life On Earth

• 1. LUCA: The 1^st cell on Earth
• A prokaryote (archaebacteria)
• Anaerobic (doesn’t need oxygen)
• Chemoautotroph (makes sugar from inorganic chemicals)

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• 2. Cyanobacteria: The 2^nd type of cell on Earth
• A prokaryote (bacteria)
• Photoautotroph (makes sugar from the suns energy in a process called photosynthesis)
• Responsible for increasing oxygen levels on Earth (will eventually cause formation of the ozone to help protect life from UV radiation)

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Stromatolites are the oldest fossils on Earth (3.5byo), produced by layers of ancient cyanobacteria

First Life On Earth

• 3. Aerobic Bacteria: the 3^rd type of cell on Earth
• Bacteria began using the free oxygen produced by cyanobacteria in a process known as aerobic cell respiration (get 38ATP/glucose instead of 2 with anaerobic)

Cell wall

Cell Membrane

DNA

Ribosomes

Plasmid

The first prokaryotic cells lived on an Earth that had little to no oxygen in its atmosphere. This means that the chemical processes that occurred within the cells, did not require oxygen.

We still have very similar cells on Earth today! Many live in the extreme temperatures of hydrothermal vents deep in the ocean or in hot springs and some live in oxygen-deprived mud. Others live in very salty water and still others in extreme alkaline or acid environments, or even in oil..

Methanogens are anaerobic archaea (bacteria) that produce methane as a byproduct - thrive in harsh environments.

Thermophiles live in environments with extreme temperatures. 

Halophiles thrive in environments with very high concentrations of salt. Many conduct photosynthesis.

Cyanobacteria Photosynthetic prokaryotes that live in the water. They are the most abundant bacteria on the planet and release large amounts of oxygen into the atmosphere.

Now Let’s Put It All Together…..

The major processes needed for the origin of life on Earth may include…

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• the presence of small organic molecules (through spontaneous synthesis shown through Miller-Urey experiment, volcanic debri, or meteorites)

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• assembly of these molecules into larger organic molecules/polymers (such as RNA and protein). RNA can self-replicate

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• the packaging of groups of molecules into microspheres that are able to maintain an internal chemistry different from surroundings (Early day cells)

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• Microspheres could have evolved into the first Prokaryotic Cells → Eukaryotic Cells

Miller and Urey’s experiment was a simulation of Earth’s early

• A. volcanic activity

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• B. formation

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• C. atmosphere

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• D. life

Miller and Urey’s experiment was a simulation of Earth’s early

• A. volcanic activity

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• B. formation

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• C. atmosphere

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• D. life

As concentrations of oxygen rose in the ancient atmosphere of Earth, organisms began to evolve

• A. anaerobic pathways.

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• B. plasma membranes.

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• C. metabolic pathways that used oxygen.

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• D. photosynthesis.

As concentrations of oxygen rose in the ancient atmosphere of Earth, organisms began to evolve

• A. anaerobic pathways.

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• B. plasma membranes.

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• C. metabolic pathways that used oxygen.

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• D. photosynthesis.

Module 1 is almost over! What to do now….

- Lesson 1.03 Quiz - Mod 1 Recap Enrichment Assign - Module 1 DBA

• Make an appointment using my scheduler.

Lesson 01.01 Exploring Life

Explain what can be considered science and how science is practiced

Identify science vs. pseudoscience

Identify what types of questions can be answered by science

Apply the scientific method to a variety of scenarios

Explain the difference between a law and theory

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Lesson 01.02 Chemistry of Life

Explain why biological macromolecules are important for everyday life

Compare the structure and function of carbohydrates, lipids, proteins, and nucleic acids

Describe how enzymes regulate chemical reactions

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Lesson 01.02A Chemistry of Life (Honors)

Explain how molecular diversity is based on the properties of carbon

Recognize the structural importance of carbohydrates, lipids, and proteins

Explain the functions of carbohydrates, lipids, and proteins

Recognize and interpret the chemical formula for the organic compounds: carbohydrates, lipids, and proteins

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Lesson 01.03 Earth’s Early Atmosphere

Describe the conditions on Earth billions of years ago

Summarize theories of how life began on Earth

Explain the connection between the beginning of life and the universal genetic code of almost all organisms

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DBA Etiquette

At the time of your DBA, please be at the number you signed up with or be in Zoom!

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Have your notes with you as an aide only….do NOT rely on these completely. I prefer you KNOW the content, obviously. :)

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Prepare as much as possible...aka Study!

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Most DBAs are back to back, so I may be a minute or two behind. Don’t fret, I will call or pull you out of the waiting room!

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