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Abiogenesis 🔧
Hypothesis & Facts
Note that a hypothesis is an idea that rationally explains something and hasn't been fully investigated. A theory is a comprehensive explanation supported by extensive evidence.
Abiogenesis is the hypothesis for which non-living matter becomes living through a natural process. It is a fact that abiogenesis has never been observed and has had several failed attempts at replication in a controlled environment, therefore it remains a hypothesis. While that alone excludes it from being a theory by definition, deductive logic and supporting evidence of steps in the process push abiogenesis as the only valid explanation for the origins of life. The question arises how, rather than if, it happened.
A spectrum of false information surrounds life science in general. Science deniers heavily use predictable debate tactics that listeners and readers should train themselves to recognize.
A straw man fallacy occurs when someone distorts or exaggerates another person’s argument, and then attacks the distorted version of the argument. This is the most common tactic for creationist arguments against evolution. For example, claiming that humans descended directly from monkeys, when in fact evolutionary theory posits a common ancestor shared by humans and modern primates. This oversimplification creates a false scientific concept riddled with holes. Then it gets used.
Shotgun argumentation is a person aiming to dominate an audience's attention with several sidestepping and immaterial details in rapid succession. giving no pause for thought or two-way dialogue. The aim is for the speaker to overwhelm the listener with the perception that they know everything and the listener knows nothing.
Chemical Process 🔧
Primarily, carbon, hydrogen, and oxygen form simple molecules that in turn combine to form both carbohydrates and, along with nitrogen, amino acids. Carbon dioxide combines with water to produce carbonic acid, an essential component of amino acids. Amino acids together form proteins.
The phosphate group is any number of binary ions attached with the PO
43– ion. Deoxyribose, and ribose are known as 5-carbon sugars. Adenine (A), cytosine (C), guanine (G), thymine (T), and uracil (U) are known as nitrogenous bases. Together, these three categories of molecules form nucleotides.
Nucleotides are cyclamate-like molecules and the
components of deoxyribonucleic acid (DNA) (National Library of Medicine) ⇗, made up of a nitrogenous base, a pentose sugar molecule, and phosphate group. They function in DNA by linking together to form the double helix structure, with the nitrogenous bases pairing up to create the genetic code. There are four types of nucleotides, the differences in their nitrogenous bases, adenine, thymine, guanine, and cytosine. Understanding the unique characteristics of each type of nucleotide is essential to comprehend how they function and interact in DNA and RNA molecules.
Nucleotides are also the building blocks of ribonucleic acid (RNA). DNA contains deoxyribose sugar while RNA contains ribose sugar, and instead of thymine uses uracil. RNA is similar to DNA but it's a separate molecule that carries out different functions in cells, including aiding in protein synthesis and gene regulation. RNA helps to essentially read genetic code and produce proteins using amino acids as the raw materials.
Ribosomes are components of cells that
translate (Khan Academy) ⇗ messenger RNA (mRNA) into instructions for processing chains of amino acids into specific sequences called polypeptides, basic protein. It is the transition point where organic molecules organize into RNA and proteins that has been elusive as conclusive evidence for abiogenesis. They create proteins for all cell types, playing a crucial role in cellular function. Ribosomes also create other ribosomes by synthesizing ribosomal proteins and ribosomal RNA (rRNA).
Proteins build muscles and tissues, repair cells, induce chemical reactions and provide structural support. They are comprised of both RNA and amino acids.
Lipids are organic molecules that are key component in the structure and stability of all cell membranes, and they also act as a barrier to govern what enters and exits a cell. Eight types of lipids are:
- Fatty acyls
- Glycerolipids
- Glycerophospholipids
- Sphingolipids
- Sterols
- Prenols
- Saccharolipids
- Polyketides
Evolution 🔧
Modern Theory 🔧
The idea that evolution is a historical rather than observational science, therefore untestable and cannot be proven, is a false belief. All science is observational and is supported with data. Evolution is a working theory.
Species change over time to adapt to their environment through genetic mutations. Genetic mutations occur randomly, and those that confer a survival advantage increase in frequency within a population, leading to evolutionary adaptation over time. Some genetic mutations can be controlled by various mechanisms such as DNA repair systems or gene silencing processes.
The control mechanisms can affect the offsprings genome during gamete formation or early embryonic development. Control mechanisms such as DNA repair systems can help fix damaged DNA before it is passed down to the next generation. Gene silencing processes can also regulate gene expression levels and prevent certain traits from being inherited.
Species survive through a breeding process called natural selection. Those better able to adapt to their environment are more likely to survive and reproduce.
Natural selection and genetic mutations are easy to confuse when looking at evidence, but are distinct processes in evolution. While mutations provide the raw material for variation, natural selection acts on this variation to drive adaptation to changing environments. Both mechanisms work together in shaping the diversity of life on Earth.
Observed Evidence 🔧
Evidence of common descent includes similarities in anatomical structures across different animals, such as limbs and organs. Fossil records demonstrate that ancient organisms had features that are found in modern-day animals and plants.
Changes in beak sizes of finches in the Galapagos Islands based on availability of different food sources is one of the most famous examples of evolution by natural selection. It played a key role in Darwin's theory of evolution by demonstrating how species can adapt to their environment over time.
Common genes to all life (355) are known as the core universal genes, and they are essential for basic cellular function.
Antibiotic resistance in bacteria is one example of genetic mutations where species change to adapt to their environment. The mutations in bacteria allow them to produce enzymes that neutralize the effects of antibiotics, much in the same fashion the human immune system starts producing cells to fight bacteria and viruses.
Mutations in sperm with increased age causing heritable mutations in offspring has been observed. This is likely a result of recent human evolution and random DNA damage accumulation. Understanding the relative contributions of these factors requires further study.
Menopause occurring later in women has been observed as a possible sign of recent human evolution, however, further research is needed to fully understand the underlying factors driving this trend. It should also be pointed out that menopause occurs earlier in most mammals compared to humans, suggesting that the prolonged reproductive capacity of human females might be a relatively recent evolutionary adaptation.
Recent human evolution includes the existence of a human gene called DARC, found in people of west Africa and most notably in the Cape Verde islands, which specifically protects individuals from malaria.
The last universal common ancestor (LUCA) refers to the single-celled organism that gave rise to all modern day life on Earth. This proto-organism lived around 4 billion years ago and likely existed in a hydrothermal vent system. No direct physical evidence exists of LUCA. Scientists use comparative genomics and molecular biology to inter its characteristics and evolutionary relationships with modern organisms.
The peppered moth evolved from light-colored to dark-colored forms in response to industrial pollution.
Meanwhile 🔧
Anatomy & Physiology 🔧
Understanding these subjects is crucial for understanding evolution because it helps us understand how organisms have adapted to their environments. By studying the structures and functions of living organisms, we can trace the evolutionary changes that have occurred to shape them into their current forms.
Ecology & Coevolution 🔧
Species within an ecosystem have an interconnectedness. Their interactions drive evolutionary changes over time. Understanding these dynamics can provide insights into the complexity and resilience of natural systems.
Human Impact on Ecosystems 🔧
Habitat destruction is a huge concern that disrupts entire ecosystems, leading to loss of biodiversity and the extinction of entire species.
Deforestation has numerous effects, the most significant being loss of biodiversity, soil erosion, increased greenhouse gases, disruption of water cycles, and negative impacts on indiginous communities.
Carbon dioxide emissions increase the amounts of CO
2 in seawater. This reacts with water to form carbonic acid. While carbonic acid is identified as a molecule necessary for life as we know it, the reaction also releases hydrogen ions which lowers the ocean's pH levels, causing acidification. This effects marine life overall, but coral and shellfish are especially damaged by this, given their calcium carbonite shells.
Overfishing, excessive fishing practices, can lead to the collapse of fisheries, damage marine ecosystems, and ultimately have a cascading effect throughout an entire ecosystem. Loss of predator species will cause overpopulation of prey species, which can in turn deplete other resources like phytoplankton and zooplankton. This damages water quality and changes the entire structure of an ecosystem.
Industrial agriculture with large-scale farming practices that focuses on efficiency and profit often results in environmental degradation and resource depletion (specifically, monoculture farming, intensive irrigation systems, and synthetic fertilizers and pesticides).
Fossil fuel emissions release greenhouse gases like carbon dioxide and methane into the atmosphere, contributing to global warming. They also release pollutants like particulate matter, nitrogen oxides, and sulfur dioxide, which cause air pollution and negatively impact human health and ecosystems.
Plastic waste harms the environment in many ways. It pollutes oceans and waterways, disrupting marine life and contaminating the food chain. It also contributes to climate change, taking hundreds of years to decompose, and while doing so, releasing toxic chemicals into the soil and air. Chemicals from plastic waste can be ingested, damaging health.
Chemical runoff from factories, pollutants released into the environment, have always been a major problem since the industrial revolution. Heavy metals like lead and mercury, volatile organic compounds, and other hazardous chemicals continue to seep into soil and groundwater and posing serious health risks.
More can be done in addition tosustainable practices, reducing pollution and being more environmentally aware of our actions. Conservation efforts like reforestation, wetland restoration, protecting natural habitats, implementing sustainable land-use practices, fashioning wildlife corridors help to counteract many of these problems.
Astrobiology 🔧
Where are all the Aliens? 🔧
The Drake equation:
$$N=R_*\cdot f_p\cdot n_e\cdot f_1\cdot f_i\cdot f_c\cdot L$$
$R_*=$ star formation rate
$f_p=$ stars with planets
$n_e=$ potentially habitable planet per star
$f_1=$ probability of habitability at any time
$f_i=$ probability of civilization
$f_c=$ probability of civilization being detectable
$L=$ length of time civilization is detectable
The Drake equation is a thought-provoking tool, but its validity is limited by the sheer number of variables involved, many of which are still purely speculative. While the equation might be based on reasonable assumptions, it remains largely hypothetical and lacks concrete evidence to support its claims. In other words, it intuitively makes sense, but there's no way to test it without first discovering any life to begin with. Regardless, it's a useful framework for sparking discussions about the possibilities of extraterrestrial life, which need to be had.
There are several possible explanations why we have not yet detected signs of extraterrestrial intelligence. These include the possibility that intelligent life is rare or short-lived, that communication across vast distances is difficult, or that intelligent civilizations may self-destruct before they can make contact with others.
Habitability Requirements 🔧
Temperature and state of water on the planet. It must be between -15 C and 122 C and with reasonable availability.
Light enough for photosynthesis, 100 AU light levels
Light and redox energy sources
UV and ionizing radiation limits
Nitrogen
Over .01 atms of O2 is needed to support life as we know it.
We're on the right track with our known habitability requirements, but we might also be overlooking some crucial factors.
Extremophiles (National Library of Medicine) ⇗ are organisms that have the ability to thrive in environments we typically consider hostile. Even they require liquid water in order to survive, but the acceptable lack of how much impedes our current understanding of what makes an environment habitable. We should also focus on the presence of complex organic compounds in conjunction with energy sources rather than just water.
The discovery of complex organic molecules in space, such as
carbonic acid (IOP Science) ⇗ suggests that the raw materials for life are widespread in the universe. The presence of carbonic acid in space could indicate the existence of water, which is essential for life as far as we know it. This increases the chances that life could emerge and thrive in environments previously considered inhospitable.
Over ten years ago, the scientific community decided that silicon-based life forms are impossible, due to the differences in silicon's chemical properties compared to carbon. However, it was a simple conclusion that doesn't entirely rule out the possibility. New discoveries and advancements in fields like biochemistry and astrobiology might challenge those earlier assessments and provide alternative perspectives.
Potentially Habitable Exoplanets 🔧
Astronomers are constantly looking for patterns in emission spectrums that indicate molecules consistent with known life in space and the atmospheres of other planets. So far they have only found a handful. In the vacuum, they have found nitrogen-carbon and hydrocarbon compounds, glycine, glycolaldehyde and ethanolamine, which are all necessary for known life to function. If those molecules are in space, then they can be introduced into anything.
Detecting planets outside of our solar system can be like playing a game of hide and seek; time consuming. But once they are found, astronomers will try to learn everything about them in the short intervals of time that they will have to see them again.
To keep up to date with exoplanets that could harbor life, visit The Planetary Habitability Laboratory @ University of Puerto Rico at Arecibo (PHL @ UPR Arecibo) -
Habitable Worlds Catalog ⇗. Although it appears it hasn't been updated in two years, it remains highly regarded and an informal primary source of information.
Now let's look at some names.
Mars
Mars has always been speculated as harboring some form of life. Recent discoveries are increasing the optimism that life was once there, even if it was only bacterial. Evidence of molecular deposits that could have only formed in liquid water have been found, as well as evidence of
carbon-cycling and organic molecules found in fatty acids (SETI Institute) ⇗. Terraforming Mars to be more habitable with our current technology is next to impossible for the fact that it is simply too cold, but that wouldn't stop us from living there under biodomes in the not-so-distant future.
K2-18b
The most promising candidate for another planet with life. It is believed to be an ocean world with a high-hydrogen atmosphere in tide lock with its host star and in the habitable zone, creating a stable environment. Detected in its atmosphere were simple carbon molecules and, inconclusively, DMS and DMDS, which are products unique to marine life on Earth. While there are no stronger signs or evidence of life, it has gained much attention and confidence that life exists there.