Where do we come from and where are we going?

References

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RNA World Hypothesis

Panspermia

Chemical Theory (Abiogenesis)

Theory of Spontaneous Generation

The different theories of the origin of life proposed throughout history

Some Theories...

Origin of life

What is life?

Camila Quintero & Patricio Novo

Where do we come from and where are we going?

• Britannica, Encyclopædia Britannica, Inc. (n.d.). Abiogenesis. [Link: https://www.britannica.com/science/abiogenesis]
• Khan Academy (n.d.). RNA world (article) | natural selection. [Link: https://www.khanacademy.org/science/ap-biology/natural-selection/origins-of-life-on-earth/a/rna-world]
• LibreTexts (2022, March 5). 3.1: Spontaneous generation. Biology LibreTexts. [Link: https://bio.libretexts.org/Bookshelves/Microbiology/Microbiology_(OpenStax)/03%3A_The_Cell/3.01%3A_Spontaneous_Generation]
• National Center for Biotechnology Information (2012, July 13). The RNA world hypothesis: The worst theory of the early evolution of life (except for all the others)(a). Biology Direct. [Link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3495036/]
• ScienceDirect (n.d.). Panspermia. Panspermia - an overview | ScienceDirect Topics. [Link: https://www.sciencedirect.com/topics/earth-and-planetary-sciences/panspermia]
• Choi, C. Q., & Dutfield, S. (2022, February 14). 7 theories on the origin of life. LiveScience. [Link: https://www.livescience.com/13363-7-theories-origin-life.html]
• Khan Academy (n.d.-a). Hypotheses about the origins of life (article). [Link: https://www.khanacademy.org/science/ap-biology/natural-selection/origins-of-life-on-earth/a/hypotheses-about-the-origins-of-life]

References (APA 7)

Scientists or researchers involved in its development

• Stanley Miller (1930-2007): An American chemist, Miller conducted the famous Miller-Urey experiment in 1953, simulating the conditions of early Earth to demonstrate that amino acids, the building blocks of proteins, could form spontaneously under these conditions.
• Harold Urey (1893-1981): Harold Urey, a Nobel laureate in chemistry, collaborated with Stanley Miller on the Miller-Urey experiment, providing valuable insights into the early Earth's conditions.
• Alexander Oparin (1894-1980): A Soviet biochemist, Oparin proposed the primordial soup theory, suggesting that life began in a "soup" of organic molecules on the early Earth.

• John Haldane (1892-1964): A British scientist, Haldane independently contributed to the concept of abiogenesis by proposing that the conditions on early Earth could have led to the spontaneous formation of organic compounds.

• Presence of Organic Compounds: Organic molecules, including amino acids, nucleotides, and sugars, have been found in meteorites and on celestial bodies, suggesting that similar processes could occur elsewhere in the universe.
• Hydrothermal Vent Chemistry: Research on hydrothermal vents at the ocean floor has shown that the conditions near these vents may have facilitated the formation of organic molecules and could have played a role in abiogenesis.

Evidence

Panspermia

• Description: Life exists throughout the universe and was brought to Earth by comets, meteorites, or cosmic dust.
• Key Figures: Fred Hoyle, Chandra Wickramasinghe.
• Evidence:
• Discovery of organic molecules in space.
• Criticisms: How life originated elsewhere remains unanswered. There is a lack of direct evidence to confirm that life or its building blocks have traveled through space and seeded other planets.

RNA World Hypothesis

• Description: RNA molecules were precursors to DNA-based life.
• Key Figures: Walter Gilbert, Carl Woese.
• Evidence:
• Self-replicating ribozymes.
• Computer simulations and experiments have shown that simple organic compounds could have led to the formation of RNA nucleotides under prebiotic conditions.

• Criticisms: While the RNA World Hypothesis explains the potential role of RNA in early life, it doesn't address the origin of RNA itself, which is a complex molecule.

Brief

Description

The origin of life refers to the scientific question of how life on Earth, or possibly elsewhere in the universe, first began. It is a fundamental and complex topic in biology, chemistry, and cosmology. Scientists have proposed various theories and hypotheses to explain how the first living organisms emerged from non-living matter.

Life is a complex and dynamic phenomenon characterized by a set of fundamental traits. It includes the capacity for growth, reproduction, metabolism (the chemical processes that sustain living organisms), response to stimuli, and the ability to adapt to changing environments. Life manifests in various forms, from microscopic single-celled organisms to the intricate diversity of multicellular plants and animals. DNA, the genetic molecule, plays a central role in storing and transmitting hereditary information. Life's origin and evolution remain subjects of scientific exploration and wonder, raising profound questions about its nature and existence beyond Earth, while influencing countless aspects of our existence.

A brief description...

Panspermia remains a topic of debate in astrobiology. Recent discoveries of organic molecules in space and the resilience of certain microorganisms to extreme conditions have fueled interest in the idea that life's building blocks or even microorganisms could potentially travel through space and seed planets. However, the exact mechanisms of panspermia and its contribution to life on Earth are still uncertain.

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Quick review...

The origin of life refers to the scientific question of how life on Earth, or possibly elsewhere in the universe, first began. It is a fundamental and complex topic in biology, chemistry, and cosmology. Scientists have proposed various theories and hypotheses to explain how the first living organisms emerged from non-living matter.

Organic Molecules in Space: Complex organic molecules, including amino acids and sugars, have been found in interstellar clouds and on comets. This suggests that the building blocks of life could exist beyond Earth. Microbes Surviving in Space: Experiments on the International Space Station have shown that certain microorganisms can survive and even thrive in the harsh conditions of space, raising the possibility that life could survive interplanetary travel.

Evidence

• Presence of Organic Compounds: Organic molecules, including amino acids, nucleotides, and sugars, have been found in meteorites and on celestial bodies, suggesting that similar processes could occur elsewhere in the universe.
• Hydrothermal Vent Chemistry: Research on hydrothermal vents at the ocean floor has shown that the conditions near these vents may have facilitated the formation of organic molecules and could have played a role in abiogenesis.

Evidence

Abiogenesis, which posits that life emerged from simple organic molecules through natural chemical processes, remains a prominent hypothesis. While the exact mechanisms are still being studied, there is substantial evidence supporting the plausibility of abiogenesis, including the synthesis of organic molecules under simulated prebiotic conditions. Ongoing research aims to elucidate the specific pathways involved.

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• Ribozymes: Ribozymes are RNA molecules capable of catalyzing chemical reactions, similar to the function of enzymes. Their discovery suggests that RNA could have acted as both genetic material and catalysts in early life.
• RNA Replication: Laboratory experiments have demonstrated that RNA molecules can replicate themselves under certain conditions, supporting the idea that RNA could have been the first self-replicating molecule.

Evidence

• Ribozymes: Ribozymes are RNA molecules capable of catalyzing chemical reactions, similar to the function of enzymes. Their discovery suggests that RNA could have acted as both genetic material and catalysts in early life.
• RNA Replication: Laboratory experiments have demonstrated that RNA molecules can replicate themselves under certain conditions, supporting the idea that RNA could have been the first self-replicating molecule.

Evidence

The RNA World Hypothesis proposes that RNA molecules played a crucial role in the early evolution of life, possibly preceding DNA-based life. This hypothesis has gained substantial support due to the discovery of ribozymes (RNA molecules with catalytic activity) and the ability of RNA to store genetic information and catalyze reactions. However, challenges, such as the spontaneous synthesis of RNA, remain areas of active research.

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Scientists or researchers involved in its development

• Aristotle (384-322 BC): One of the earliest proponents of the theory. He believed that animals like insects, frogs, and mice could spontaneously generate from mud, dung, and other organic substances.
• Francesco Redi (1626-1697): Italian physician and scientist, who conducted experiments in the 17th century to challenge the theory. He showed that maggots did not spontaneously generate from meat but instead came from fly eggs.

• Louis Pasteur (1822-1895): The French chemist and microbiologist played a pivotal role in disproving spontaneous generation in the mid-19th century. His experiments with swan-necked flasks demonstrated that microorganisms only appeared when exposed to preexisting microorganisms, supporting the idea of biogenesis.

• Louis Pasteur (1822-1895): While not a proponent of panspermia, Pasteur's work on disproving spontaneous generation indirectly supported the idea that life must have an external source.

Scientists or researchers involved in its development

• Fred Hoyle (1915-2001): The British astrophysicist and cosmologist, along with his colleague Chandra Wickramasinghe, was one of the early proponents of panspermia. He suggested that life's complexity made it unlikely to have originated solely on Earth.
• Chandra Wickramasinghe (born 1939): An astronomer and astrobiologist, Wickramasinghe collaborated with Fred Hoyle and conducted research on comets and their potential role in panspermia.

Theory of Spontaneous Generation

• Description: Early belief that life could arise spontaneously from non-living matter. It posited that certain organisms could emerge fully formed from decaying organic material.

• Key Figure: Aristotle, Francesco Redi, Louis Pasteur.
• Evidence:
• Redi's experiment with meat and flies.
• Pasteur's experiments with swan-necked flasks.
• Criticisms: Lack of modern understanding of microbiology. Disproven by Empirical Evidence and advancements in Microscopy.

Abiogenesis

• Description: Life on Earth originated from non-living matter through a series of chemical processes. It proposes that the complex molecules necessary for life gradually form from simple organic compounds.

• Key Figures: Stanley Miller, Harold Urey.
• Evidence:
• Miller-Urey Experiment
• Presence of Organic Compounds
• Hydrothermal Vent Chemistry
• Criticisms: Complex biological molecules not produced. The transition from simple organic molecules to complex life forms is not fully explained leaving a gap in understanding the origin of cellular life.

• Günter Blobel (1936-2018): Blobel's research on protein targeting and signal sequences added to the evidence supporting the RNA World Hypothesis by suggesting that RNA molecules could have played a role in the early cellular processes.

Scientists or researchers involved in its development

• Walter Gilbert (born 1932): The American biochemist and Nobel laureate was one of the early proponents of the RNA World Hypothesis. He proposed that RNA could have served as the first genetic material and catalytic molecules.
• Sidney Altman (born 1939) and Thomas Cech (born 1947): Both Altman and Cech independently discovered ribozymes, which are RNA molecules capable of catalyzing chemical reactions. Their work provided support for the idea that RNA could have functioned as both genetic material and enzymes.

This theory has been widely discredited in modern science. The experiments conducted by Louis Pasteur in the 19th century demonstrated that life does not spontaneously arise from non-living matter, as previously believed. It is considered obsolete and contradicted by the principles of biology and biochemistry. It paved the way for the acceptance of the Biogenesis theory, which states that life arises from preexisting life.

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Organic Molecules in Space: Complex organic molecules, including amino acids and sugars, have been found in interstellar clouds and on comets. This suggests that the building blocks of life could exist beyond Earth. Microbes Surviving in Space: Experiments on the International Space Station have shown that certain microorganisms can survive and even thrive in the harsh conditions of space, raising the possibility that life could survive interplanetary travel.

Evidence