Unit 7 Topic 3.1: Early Origins Flashcards
1
Q
The oldest crust fragment on Earth is the…
Origin of the Non-Living Earth Systems: “when and what was the first solid surface to form on Earth?”
A
Acasta Gneiss
- A metamorphic rock deformed by high pressure and temperature
- Before metamorphism, was a granite-like rock in an ancient continent
2
Q
Estimates regarding the onset of plate tectonics range widely:
Initiation of plate tectonics
A
4 billion years ago to as recent as 800 million years
3
Q
Evidence of the onset can be found within…
A
Diamonds
4
Q
How are diamonds within the mantle brought to the surface?
Evidence of the onset can be found within diamonds - WHY/HOW?
A
via volcanic activity
5
Q
During their formation, diamonds incorporate certain materials in to their structure - what do these inclusions tell us?
Evidence of the onset can be found within diamonds - WHY/HOW?
A
These “inclusions” have been examined to reveal a shift in chemical composition of diamond inclusions approximately 3 billion years ago
6
Q
What were earlier diamond inclusions made of?
Evidence of the onset can be found within diamonds - WHY/HOW?
A
In earlier inclusions, peridotite - the rock making up most of Earth’s mantle - was the predominant material
7
Q
What are recent diamond inclusions made of?
Evidence of the onset can be found within diamonds - WHY/HOW?
A
- In recent inclusions, diamonds contain eclogite - which forms when oceanic crust has been discovered with an age exceeding roughly 3.2 Ga
- Before 3.2 Ga, Earth’s mantle may have been too hot (and therefore buoyant) to allow the lithosphere to subduct
8
Q
The atmosphere
How is it retained? How is it protected?
A
The atmosphere, or “air” of Earth is retained by gravity and protected from the effects of solar radiation (which has the potential to strip away the atmosphere over time) by Earth’s magnetosphere
9
Q
The evolution of the atmosphere - initial state
+ WHEN DID IT CHANGE
A
- The atmosphere has evolved over time - initially, earth would have an atmosphere similar to the gases in the solar nebula: mostly hydrogen and helium
- However, solar winds would have stripped these gases away from the earth when the sun initiated nuclear fusion
10
Q
The evolution of the atmosphere - the next atmosphere
HOW DID IT DEVELOP? WHAT’S ITS COMPOSITION?
A
Developed volcanically as the hot interior “outgassed,” a process still occurring today.
The composition would be similar to current volcanic gas emissions:
- Carbon dioxide
- Hydrogen
- Nitrogen
- Chlorine
- Sulphur-based gases
- Water
11
Q
The evolution of the atmosphere - the next atmosphere
HOW DID IT SURVIVE?
A
Unlike Earth’s initial atmosphere, the formation of Earth’s core and the magnetosphere would allow this atmosphere to be retained.
12
Q
The evolution of the atmosphere - the next atmosphere
COMPOSITION VS. TODAY
A
- It is estimated that water would have made up around 60% of this atmospheric phase, with carbon dioxide varying between 10 and 40%.
- Compare that to today, where nitrogen comprises approximately 78%, oxygen 21%, 1% Argon and trace amounts of carbon dioxide and other gasses
13
Q
Why/how does so much nitrogen comprise our modern atmosphere?
A
- Where did the nitrogen come from? Volcanoes as the planet degassed
- Unlike gasses such as carbon dioxide, very few “nitrogen sinks” can take the gas out of the atmosphere and store it elsewhere (essentially it has nowhere to go)
- As such, nitrogen has gradually built up to its current 78% level over time.
14
Q
Why/how does oxygen comprise our modern atmosphere?
A
- From photosynthesizing cyanobacteria that released oxygen as a waste product
15
Q
Why/how does iron comprise our modern atmosphere?
A
- Iron in its Ferrous soluble state (Fe2+) was present in high concentrations dissolved in the Earth’s oceans, added through hydrothermal vent systems on the ocean floor
- The oxygen produced by the cyanobacteria would rapidly oxidize the dissolved Ferrous to Ferric (Fe3+) minerals in the oceans.
- Ferric iron is insoluble, and this process probably accounts for the deposits of iron-rich rocks called Banded Iron Formations.
- Eventually, though, the amount of oxygen produced by cyanobacteria not only oxidized all the Ferrous iron in the oceans, but the excess could bubble out of the oceans and start accumulating in the atmosphere, oxidizing any iron minerals on land
16
Q
Oceans form the major component of the Hydrosphere, but where does all that water come from?
ASTEROIDS
The Hydrosphere
A
- Asteroids, particularly carbonaceous chondrites
- These asteroids, rich in water-bearing minerals, likely delivered significant amounts of water to our planet during its early history.
- As these asteroids collided with Earth, the impact would have released the bound water, contributing to the formation of our oceans.
17
Q
Oceans form the major component of the Hydrosphere, but where does all that water come from?
VOLCANIC ACTIVITY
A
- During the planet’s formation, water-rich materials were incorporated into its interior
- Over time, this water has been gradually released from Earth’s mantle via volcanic activity.
- This process, known as outgassing, has replenished the oceans and atmosphere.
- It also accounts for why Earth’s mantle today is relatively “dry.”
18
Q
What is life? DEFINITION
The Biosphere
A
- The condition that distinguishes animals, plants, bacteria, and archaea (a type of microorganism) from inorganic matter.
- Characteristics of life include being separated from the external environment by a barrier and possessing the capacity for growth, reproduction, functional activity, and evolution.
19
Q
What is emergence and why is it significant to the biosphere?
A
- Emergence: the combination of simple components results in the emergence of complex behaviours and structures that are not present in the individual components alone
- EX: an ant vs an ant colony
20
Q
What is entropy?
Life vs. universe
A
- Entropy: the name given to how the universe, over time, becomes increasingly disordered and energy becomes spread out.
- The universe’s ultimate fate is to become very cold and disorganized with no structures like stars or galaxies, the so-called heat death of the universe.
- Life, however, works in the opposite direction to entropy; it locally creates order and concentrates rather than spreads energy out. Of course, entropy eventually wins out when organisms die.
21
Q
Cellular life can be divided into three major domains:
A
- Bacteria
- Archaea
- Eukaryotes
22
Q
Bacteria and Archaea
Cellular life can be divided into three major domains:
A
- Classified as prokaryotes, single-celled organisms that do not have a nucleus enclosed by a membrane.
- Instead, their genetic material is freely floating in the cytoplasm.
- Unlike eukaryotic cells, prokaryotes also lack complex organelles; specialized cellular structures that perform specific functions.
23
Q
Eukaryotes
Cellular life can be divided into three major domains:
A
- Eukaryotes are **organisms whose cells have a membrane-bound nucleus containing their genetic material. **
- They also possess complex organelles, specialized cellular structures that perform specific cellular functions.
- Eukaryotes include protists, plants, fungi, and animals.
- In general, larger than prokaryotic cells
24
Q
All cellular life-forms exhibit the following 5 features:
A
- They work to maintain homeostasis (a stable internal environment) within the cells.
- They generate energy to power cellular processes.
- They possess a membrane that separates them from the external environment, creating a closed system.
- They have molecules (DNA and RNA) containing information for building structures within the cell.
- The information molecules must have the capacity to evolve via natural selection as reproduction passes copies into the future.
25
Are viruses considered living organisms?
## Footnote
WHY IS THIS DEBATED?
* **Can only reproduce by hijacking the machinery of a host cell.**
* Unlike cells, they **cannot produce their own energy** or **maintain homeostasis.**
* One interesting question is whether viruses or cells evolved first.
26
On Earth, which element preferred for life
## Footnote
Origin of Life's Building Blocks
* Carbon - can form strong bonds with itself and other elements, creating a wide variety of molecules with diverse properties
27
On Earth, which element preferred for life
| Why choose carbon over silicon?
## Footnote
Origin of Life's Building Blocks
* Although silicon is more abundant in Earth's crust and can also form complex molecules, **life is probably carbon-based because carbon bonds are generally *stronger* and more *stable* in water than silicon bonds**
28
All living organisms are made up of what types of cells?
* All living organisms, **except for viruses**, are made up of cells composed of various **organic molecules**.
* These molecules include **carbohydrates**, **lipids** (fats), **amino acids** (the building blocks of proteins), and **nucleobases** (the "letters" of the genetic code in DNA and RNA).
29
What exactly are organic molecules made of?
* Organic molecules are compounds containing **carbon and hydrogen atoms**.
* Organic molecules were initially called "organic" because it was once believed that only living organisms could create them
* However, we now know that organic molecules can also be formed naturally in the non-living universe without the involvement of life.
30
Where else can organic molecules be formed in the non-living universe?
## Footnote
Overview
* Extraterrestrial Sources
* Atmospheric Sources
* Oceanic Hydrothermal Vents
31
What organic molecules have beem found in earth?
## Footnote
Where else can organic molecules be formed in the non-living universe?
* Our planet likely received some of its organic building blocks from space.
* Detected organic molecules called **polycyclic aromatic hydrocarbons (PAHs)** in nebulae within our galaxy: ring-like structures that sometimes form spheres called "buckyballs"
* It's estimated that around 20% of all the carbon in the universe might be PAHs.
32
What types of meteorites containing organic molecules have been found?
## Footnote
Where else can organic molecules be formed in the non-living universe?
* **Carbonaceous chondrite meteorites**, like the Murchison meteorite in Australia, have been found to contain a variety of organic molecules, including over **15 different amino acids**, the building blocks of proteins!
* Similarly, analysis of material collected from **comet Wild 2** by NASA's Stardust mission in 2009 revealed the presence of the **amino acid glycine and other organic compound**s.
* These discoveries strongly suggest that some organic molecules essential for life on Earth may have originated in space and arrived here through meteorites and comets.
33
Atmospheric Sources
## Footnote
Where else can organic molecules be formed in the non-living universe?
* Urey-Miller experiment: analysis of liquid detected a variety of amino acids.
* Ideas regarding the composition of Earth's early atmosphere have changed since the original experiment; even so, the experiment still readily synthesizes many of life's building blocks with different atmospheric starting materials.
* **It is possible that organic molecules were literally "raining" from the skies of the Early Earth**
34
Oceanic Hydrothermal Vents
## Footnote
Where else can organic molecules be formed in the non-living universe?
* For a more geological origin of organic molecules, we need to consider hydrothermal vents
* **Hydrothermal vents occur in two locations on the ocean floor**, both characterized by plumes of hot water escaping from the Earth's crust.
35
**Hydrothermal vents occur in two locations on the ocean floor**
## Footnote
Where else can organic molecules be formed in the non-living universe?
1. On-Axis "Mid Ocean" Ridge Vent Systems
2. Off-Axis Vent Systems
36
On-Axis "Mid Ocean" Ridge Vent Systems - how do they work?
## Footnote
Where else can organic molecules be formed in the non-living universe?
* "on-axis" meaning the **active ridge axis of a divergent boundary**
* Water seeps down through fractures and faults in the crust and is superheated by the hot rocks and magma at depth.
37
On-Axis "Mid Ocean" Ridge Vent Systems - what color are they?
## Footnote
Where else can organic molecules be formed in the non-living universe?
* The fluids released at hydrothermal vents at midocean ridges are **black**, very **hot** (250 - 400°C) and **acidic**
* The black colour is **caused by iron sulphide stripped from rocks as the hot water travels through the crust. **
38
How were On-Axis "Mid Ocean" Ridge Vent Systems thought to generate organic molecules?
## Footnote
Basically the cons of this
* Initially, **it was thought the minerals in these systems could have acted as catalysts**, helping to form organic molecules from CO2 dissolved in seawater.
* Unfortunately, **any organics that may form in this environment would remain stuck to the mineral catalysts, making them unusable.**
* In addition, although these vent systems support a diverse ecosystem today, **it is unlikely that such hot and acidic waters would have been favourable for forming relatively delicate organic molecules needed for life**.
* Another problem lies in the activity in these systems; activity on a ridge can be sporadic and remain inactive for long periods.
39
Off-Axis Vent Systems - where are they located?
By "off-axis," we mean that these vents **are not located on the active axis of the spreading ridge** but quite a distance **away from the volcanically active ridge systems.**
40
Off-Axis Vent Systems - what color do they produce?
* Rather than "black smokers," these off-axis systems are characterized by **"white smokers"**
* Barium, calcium, and silicon minerals produce the lighter colour in these systems.
* Although still very warm compared to the surrounding ocean water, white smoker vents are cooler (around 60-90°C) and are alkaline with a pH of around 9, similar to baking soda.
41
Off-Axis Vent Systems - Since these regions are no longer volcanically active, **what fuels the activity at these hydrothermal vent systems?**
* The process of serpentinization plays a key role.
* Areas with white smokers are often **located near faults that have brought deep oceanic lithosphere material** - **peridotite** - **closer to the surface, allowing seawater to interact with these rocks.**
* When seawater encounters the mineral **olivine** in peridotite, an **exothermic (heat-generating) chemical reaction occurs.**
* **Oxygen from the seawater combines with iron in the olivine, creating magnetite and releasing hydrogen gas**.
* **The hydrogen produced can react with dissolved carbon dioxide in the seawater to form organic molecules**
42
Why do off-axis vent systems have a longer lifespand?
* Unlike vent systems at mid-ocean ridges, off-axis vent systems are not dependent on volcanic activity and, therefore, have a much longer lifespan and the possibility of producing more complex organics over a longer periods of time.
43
How do you go from a soup of organic molecules to the first living cells?
| What 2 things do you need?
## Footnote
From Building Blocks to Cells
* To form a cell, **you need molecules that can store information that directs cell activities and can be replicated to create copies of themselves and the cell in the future**.
* You also need a membrane that isolates cell contents from the external environment.
44
Replicating Molecules - most life uses DNA; how did this come about?
## Footnote
From Building Blocks to Cells
* Today, most life uses DNA to encode all the instructions for cell activities, including producing proteins that form cellular structures.
* **DNA can only be replicated by *enzymes composed of proteins.***
* The information needed to create these enzymes is encoded in DNA.
* This creates a classic chicken and egg situation: You can't have the DNA without the enzymes, and you can't have enzymes without the DNA—a paradox!
45
How have scientists explained the DNA paradox?
## Footnote
From Building Blocks to Cells
* To circumvent this paradox, scientists have suggested that the **first cells on Earth did not use DNA but a similar yet simpler molecule called RNA**
* Both RNA and DNA are composed of units called nucleotides comprising a photoshate, a sugar and a base.
46
Differences between RNA and DNA
* **Sugars**: In DNA, the sugar is deoxyribose, while in RNA, ribose is used.
* **Bases**: The bases (which form the "letters" in the genetic code) are G, U, A, and C in RNA (each letter representing a different type of base), but in DNA, U is replaced by T.
* **# of strands:** In addition, RNA is composed of a single strand, unlike the double helix of DNA (Figure 12-right).
* **RNA can replicate itself without the aid of specialized enzymes.**
* It can also fold itself into various shapes and engage in activities that resemble metabolism.
* This has led to the development of the RNA world hypothesis, which suggests that one of the first and probably most significant steps towards the evolution of life is closely associated with RNA.
47
Cell Membranes
| What do they do?
## Footnote
From Building Blocks to Cells
* The development of cell membranes was a crucial step in the evolution of life.
* **Membranes allow beneficial molecules to be concentrated, increasing the likelihood of interesting chemical reactions. **
* **They also isolate the cell's contents from the external environment, creating a more stable internal environment** (*homeostasis*).
48
Composition of cell membranes
## Footnote
From Building Blocks to Cells
* Cell membranes are **primarily composed of layers of fatty acids**
* Fatty acids are lipid molecules with water-loving (hydrophilic) heads and water-hating (hydrophobic) tails.
* In water, they spontaneously form bilayers with tails facing inward and heads facing outward
* These bilayers can also form spheres called liposomes, which have hydrophobic heads both on the outside and inside, surrounding a central water-filled cavity.
49
How do liposomes demonstrate the potential of fatty acid bilayers to concentrate organic molecules?
* This might have been a mechanism that contributed to the formation of **"protocells,"** early precursors of cellular life.
* However, **cellular membranes are more complex structures that, in addition to lipid bilayers, have evolved sophisticated machinery to facilitate transport between the cell and its surroundings.**
50
Organic Molecules and Catalysts
## Footnote
Where Did Life Emerge?
* The alkaline fluid flowing through **off-axis vents** moves much slower than the acidic, superheated water of black smokers.
* Instead of flowing through a large chimney-like structure, the water percolates through a network of tiny interconnected pores ranging from micrometres to millimetres.
* **The slower flow rate in this system allows any organic molecules that form to reside there for *longer periods*, increasing their concentration and enabling more complex reactions.**
* Additionally, the longevity of these alkaline vent systems, often exceeding 100,000 years, makes them more favourable candidates for the origin of life compared to black smokers, which tend to collapse within a few decades.
51
How were alkaline vents in the past different than ones we use today?
## Footnote
Where Did Life Emerge?
* Over 4 billion years ago, **oceans lacked dissolved oxygen and contained much higher concentrations of dissolved (ferrous) iron.**
* The **higher levels of atmospheric CO2** (10-40% of atmospheric gases, compared to 0.4% today) **would have allowed more CO2 to dissolve in the oceans.**
* **This CO2 would react with water to form carbonic acid**, making the oceans more acidic with a pH of 5-7 compared to today's 8.1.
* These conditions would have **promoted the precipitation of iron hydroxides and sulphides rather than iron oxides on the walls of the vent pores.**
* This is significant because iron sulphides, along with other metals like nickel and molybdenum, are **essential components of catalytic molecules found in enzymes today.**
52
Metabolism and Cell Membranes
* The difference in acidity (proton concentration) between the **alkaline vent fluids** and the **surrounding environment** creates a **proton concentration gradient similar to the one found in mitochondria**
* Organic materials evolving within these vents could have harnessed this natural flow of protons as an energy source to drive chemical reactions.
53
How have **the pores in hydrothermal vents served as templates for the earliest cells.**
* Additionally, experiments have shown that the micropores in these vents and their associated chemical reactions can generate fatty acids, which could have formed the first cell membranes, further isolating and concentrating cellular contents.
* Over time, with the development of more sophisticated membranes and cellular machinery, life may have learned to create its own proton gradient without relying on the vents, enabling it to venture out and populate the oceans.
54
Evidence from LUCA
## Footnote
Where did life emerge?
* LUCA, an acronym for the **Last Universal Common Ancestor, is the common ancestor of all life on Earth today**
* By studying the genomes of all living organisms, scientists have determined that this ancestor lies at the branching point between **archaea and bacteria**, with eukaryotes evolving later along the archaea branch.
* Scientists identified the oldest genes shared by all life, which LUCA must have also possessed.
* This analysis reveals that LUCA had genes involved in metabolizing hydrogen and carbon dioxide, and that metals like iron, nickel, and molybdenum were crucial for these processes.
* All of these elements could have been found in alkaline vent systems. While this is not conclusive evidence for the nature and origin of the first life form, it certainly sheds light on the characteristics of these ancient microbes and supports the off-axis hypothesis.
