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7.13 Origin of Life on Earth

6 min readjanuary 13, 2023

Jed Quiaoit

Jed Quiaoit

Samantha Himegarner

Samantha Himegarner

Jed Quiaoit

Jed Quiaoit

Samantha Himegarner

Samantha Himegarner

When Did Life Start?

The is a topic of ongoing scientific research, and several hypotheses have been proposed to explain how life first emerged on our planet. These hypotheses are supported by various types of scientific evidence, including geological, chemical, and biologic. 🌎

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-3qHXrvB3FzYo.jpg?alt=media&token=91ec4ab8-5098-4d1f-92e5-55db2d1717b5

Source: UW Madison News

Geological evidence provides support for models of the by providing information about the conditions on the planet during its early history.

For example, it is known that Earth formed approximately 4.6 billion years ago (bya), and that the environment was too hostile for life until about 3.9 bya. This is based on evidence from the geological record, such as the composition of the early atmosphere, the presence of liquid water, and the intensity of the sun's radiation. By understanding the conditions of the early Earth, scientists are able to construct models of how life could have emerged under those conditions.

Additionally, the earliest fossil evidence for life on Earth dates to around 3.5 bya. This is based on the discovery of fossilized stromatolites, which are layered structures formed by ancient microbial communities. These fossils provide strong evidence that life existed on Earth at least 3.5 billion years ago, and they also provide insight into the nature of that early life.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-W1hGqGmUWNn6.jpg?alt=media&token=b2a0e9c8-a597-4e25-9782-ee3f2681dead

Source: BBC

Taken together, the evidence from geology, chemistry, and biology provides a plausible range of dates when the origin of life could have occurred. For example, based on the geological evidence, scientists believe that life could have emerged on Earth as early as 3.9 bya and as late as 3.5 bya. However, remember that the origin of life is a complex process and still not fully understood and the range of possible dates could be refined as new discoveries and technologies emerge.

Modeling Life's Origin

There are several models about the , each of which proposes a different explanation for how life first emerged on our planet. These models can be broadly divided into two main categories: and .

One model of is the "primitive Earth" model. This model proposes that life emerged on Earth through the gradual synthesis of organic molecules from . According to this model, the primitive Earth provided the necessary conditions for this synthesis to occur, such as the presence of available free energy and the absence of a significant quantity of atmospheric oxygen (O2). This model suggests that the first living organisms were simple, self-replicating molecules that formed spontaneously through chemical reactions in the early Earth's oceans. 🪐

Another model is the "" model, which proposes that organic molecules were transported to Earth by a meteorite or other celestial event. This model suggests that the organic molecules that make up life, such as and , were formed in the dust clouds of other planets or in comets and . These molecules could have then been transported to the early Earth by comets or , where they assembled into the first living organisms. ☄️

Current scientific understanding suggests that it's likely that multiple mechanisms were involved. Both models have evidence to support them and it's not mutually exclusive. For example, it's possible that both and could have contributed to the , with forming on Earth and organic molecules being brought by , and the combination of these factors led to the emergence of life on Earth! Hopefully we find out the truth soon...

What Does the Chemistry Tell Us?

have shown that it is possible to form complex organic molecules from inorganic molecules in the absence of life. This is known as , the process of the origin of life from non-living matter. These experiments have been critical in shedding light on the early stages of the emergence of life on Earth, and have provided evidence to support models of the origin of life that propose that life emerged through the gradual synthesis of organic molecules from . 🌱

As briefly described in the previous section, one of the key aspects of these experiments is the formation of organic molecules or monomers from inorganic precursors. These organic molecules, such as and , served as building blocks for the formation of more complex molecules. Scientists have been able to demonstrate that these organic molecules can be formed under conditions that are thought to have existed on the early Earth, such as in the presence of available free energy and the absence of a significant quantity of atmospheric oxygen (O2).

The joining of these monomers produced , which are long chains of repeating units. These have the ability to replicate, store, and transfer information, which are the hallmarks of life. For example, , such as , store and transfer genetic information, and proteins, such as , catalyze chemical reactions. The formation of these is an important step in the emergence of life, as they allow the replication and evolution of the first living organisms.

RNA's Role in the Puzzle

The RNA World Hypothesis is a widely accepted model for the origin of life that proposes that RNA (ribonucleic acid) could have been the earliest genetic material. According to this hypothesis, RNA was the first molecule to emerge that had the ability to store and transmit genetic information, catalyze chemical reactions and replicate itself.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-CYo6MU3jUPs4.jpg?alt=media&token=d78f9311-62fc-4507-963c-e0c49e595d9c

Source: Quanta Magazine

The RNA World Hypothesis proposes that RNA molecules were the first on Earth, and that they gradually gave rise to more complex forms of life, such as the emergence of DNA and proteins. It suggests that RNA was able to perform all three functions of life: storing and transmitting genetic information, catalyzing chemical reactions and replicating itself. This idea supports the idea that RNA was a "jack of all trades" molecule that could have been the precursor to all other forms of genetic material, such as DNA and proteins. 🎃

One of the key pieces of evidence for the RNA World Hypothesis is the ability of RNA to act as both a genetic molecule and a catalyst. Scientists have been able to demonstrate that RNA can catalyze a wide range of chemical reactions, including those that are essential for life, such as the , the formation of and the . This ability of RNA to catalyze reactions is thought to have been critical for the emergence of life, as it would have allowed for the formation of more complex molecules and the replication of RNA molecules.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-wAKCOexej3SJ.jpeg?alt=media&token=d8ff9dba-b62e-4d60-8cc4-599be46021e1

Source: BioNinja

Additionally, the RNA World Hypothesis also offers explanations for how the first self-replicating RNA molecules could have formed. It proposes that RNA could have formed through the gradual in the presence of suitable catalysts, such as and other inorganic catalysts. 🧱

Key Terms to Review (21)

Origin of Life on Earth

: The origin of life on Earth refers to the process and timeline by which life first emerged on our planet, a subject of ongoing scientific research. It is generally accepted that this occurred around 3.9 billion years ago.

Abiogenesis

: Abiogenesis is the process by which life arises naturally from non-living matter, such as simple organic compounds.

Fossilized Stromatolites

: Fossilized stromatolites are layered rock formations created by the growth of microorganisms, particularly cyanobacteria. They are some of the oldest known fossils on Earth, dating back over 3.5 billion years.

Panspermia

: Panspermia is the hypothesis that life exists throughout the Universe, distributed by space dust, meteoroids, asteroids, comets, planetoids and also by spacecraft carrying unintended contamination by microorganisms.

Atmospheric Oxygen (O2)

: Atmospheric oxygen refers to the oxygen present in Earth's atmosphere. It makes up about 21% of our atmosphere and is essential for aerobic respiration in many organisms.

Primitive Earth Model

: The primitive earth model is a scientific theory that describes the conditions and environment of early Earth, around 4.5 billion years ago.

Amino Acids

: Amino acids are organic compounds that combine to form proteins. They are fundamental building blocks of life and necessary for numerous bodily functions.

Nucleotides

: Nucleotides are the building blocks of nucleic acids like DNA and RNA. Each nucleotide is composed of a sugar, a phosphate group, and a nitrogenous base.

Meteorites

: Meteorites are pieces of rock or metal from space that have survived their journey through Earth's atmosphere and landed on our planet's surface.

Chemical Experiments

: Chemical experiments involve combining or manipulating substances to observe the resulting chemical reactions, often to test a hypothesis or understand a chemical process.

Inorganic Precursors

: These are simple compounds, often containing elements like carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur, which participate in chemical reactions to form more complex molecules.

Organic Molecules or Monomers

: These are small molecules that can join together with other similar molecules to form larger structures known as polymers. They contain carbon atoms and are often found in living organisms.

Polymers

: Large molecules made from many smaller units called monomers linked together in a chain. Examples include proteins (polymers of amino acids), DNA (polymers of nucleotides), and polysaccharides (polymers of sugars).

DNA and RNA

: DNA (Deoxyribonucleic Acid) is a molecule that carries most of the genetic instructions used in growth, development, functioning and reproduction. RNA (Ribonucleic Acid) plays crucial roles in coding, decoding, regulation and expression of genes.

Enzymes

: Enzymes are biological catalysts that speed up chemical reactions in living organisms without being consumed in the process.

Nucleic Acids

: Nucleic acids are large biomolecules essential for all known forms of life. They carry genetic information and include DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).

Self-Replicating Entities

: These are entities that can make copies of themselves. In biology, this often refers to molecules such as DNA and RNA.

Peptide Bonds

: A peptide bond is a chemical bond formed between two amino acids when the carboxyl group of one reacts with the amino group of another, releasing water (a dehydration reaction).

Synthesis of Sugars

: This refers to how living organisms create simple sugars like glucose from non-carbohydrate precursors through processes like photosynthesis or gluconeogenesis.

Clay Minerals

: A group of hydrous aluminium phyllosilicates minerals that may contain minor amounts of other elements such as potassium, magnesium iron etc., typically formed over long periods through weathering processes.

Polymerization of Nucleotides

: The process by which nucleotides (the building blocks of DNA and RNA) are linked together to form a long chain, or polymer.

7.13 Origin of Life on Earth

6 min readjanuary 13, 2023

Jed Quiaoit

Jed Quiaoit

Samantha Himegarner

Samantha Himegarner

Jed Quiaoit

Jed Quiaoit

Samantha Himegarner

Samantha Himegarner

When Did Life Start?

The is a topic of ongoing scientific research, and several hypotheses have been proposed to explain how life first emerged on our planet. These hypotheses are supported by various types of scientific evidence, including geological, chemical, and biologic. 🌎

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-3qHXrvB3FzYo.jpg?alt=media&token=91ec4ab8-5098-4d1f-92e5-55db2d1717b5

Source: UW Madison News

Geological evidence provides support for models of the by providing information about the conditions on the planet during its early history.

For example, it is known that Earth formed approximately 4.6 billion years ago (bya), and that the environment was too hostile for life until about 3.9 bya. This is based on evidence from the geological record, such as the composition of the early atmosphere, the presence of liquid water, and the intensity of the sun's radiation. By understanding the conditions of the early Earth, scientists are able to construct models of how life could have emerged under those conditions.

Additionally, the earliest fossil evidence for life on Earth dates to around 3.5 bya. This is based on the discovery of fossilized stromatolites, which are layered structures formed by ancient microbial communities. These fossils provide strong evidence that life existed on Earth at least 3.5 billion years ago, and they also provide insight into the nature of that early life.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-W1hGqGmUWNn6.jpg?alt=media&token=b2a0e9c8-a597-4e25-9782-ee3f2681dead

Source: BBC

Taken together, the evidence from geology, chemistry, and biology provides a plausible range of dates when the origin of life could have occurred. For example, based on the geological evidence, scientists believe that life could have emerged on Earth as early as 3.9 bya and as late as 3.5 bya. However, remember that the origin of life is a complex process and still not fully understood and the range of possible dates could be refined as new discoveries and technologies emerge.

Modeling Life's Origin

There are several models about the , each of which proposes a different explanation for how life first emerged on our planet. These models can be broadly divided into two main categories: and .

One model of is the "primitive Earth" model. This model proposes that life emerged on Earth through the gradual synthesis of organic molecules from . According to this model, the primitive Earth provided the necessary conditions for this synthesis to occur, such as the presence of available free energy and the absence of a significant quantity of atmospheric oxygen (O2). This model suggests that the first living organisms were simple, self-replicating molecules that formed spontaneously through chemical reactions in the early Earth's oceans. 🪐

Another model is the "" model, which proposes that organic molecules were transported to Earth by a meteorite or other celestial event. This model suggests that the organic molecules that make up life, such as and , were formed in the dust clouds of other planets or in comets and . These molecules could have then been transported to the early Earth by comets or , where they assembled into the first living organisms. ☄️

Current scientific understanding suggests that it's likely that multiple mechanisms were involved. Both models have evidence to support them and it's not mutually exclusive. For example, it's possible that both and could have contributed to the , with forming on Earth and organic molecules being brought by , and the combination of these factors led to the emergence of life on Earth! Hopefully we find out the truth soon...

What Does the Chemistry Tell Us?

have shown that it is possible to form complex organic molecules from inorganic molecules in the absence of life. This is known as , the process of the origin of life from non-living matter. These experiments have been critical in shedding light on the early stages of the emergence of life on Earth, and have provided evidence to support models of the origin of life that propose that life emerged through the gradual synthesis of organic molecules from . 🌱

As briefly described in the previous section, one of the key aspects of these experiments is the formation of organic molecules or monomers from inorganic precursors. These organic molecules, such as and , served as building blocks for the formation of more complex molecules. Scientists have been able to demonstrate that these organic molecules can be formed under conditions that are thought to have existed on the early Earth, such as in the presence of available free energy and the absence of a significant quantity of atmospheric oxygen (O2).

The joining of these monomers produced , which are long chains of repeating units. These have the ability to replicate, store, and transfer information, which are the hallmarks of life. For example, , such as , store and transfer genetic information, and proteins, such as , catalyze chemical reactions. The formation of these is an important step in the emergence of life, as they allow the replication and evolution of the first living organisms.

RNA's Role in the Puzzle

The RNA World Hypothesis is a widely accepted model for the origin of life that proposes that RNA (ribonucleic acid) could have been the earliest genetic material. According to this hypothesis, RNA was the first molecule to emerge that had the ability to store and transmit genetic information, catalyze chemical reactions and replicate itself.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-CYo6MU3jUPs4.jpg?alt=media&token=d78f9311-62fc-4507-963c-e0c49e595d9c

Source: Quanta Magazine

The RNA World Hypothesis proposes that RNA molecules were the first on Earth, and that they gradually gave rise to more complex forms of life, such as the emergence of DNA and proteins. It suggests that RNA was able to perform all three functions of life: storing and transmitting genetic information, catalyzing chemical reactions and replicating itself. This idea supports the idea that RNA was a "jack of all trades" molecule that could have been the precursor to all other forms of genetic material, such as DNA and proteins. 🎃

One of the key pieces of evidence for the RNA World Hypothesis is the ability of RNA to act as both a genetic molecule and a catalyst. Scientists have been able to demonstrate that RNA can catalyze a wide range of chemical reactions, including those that are essential for life, such as the , the formation of and the . This ability of RNA to catalyze reactions is thought to have been critical for the emergence of life, as it would have allowed for the formation of more complex molecules and the replication of RNA molecules.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-wAKCOexej3SJ.jpeg?alt=media&token=d8ff9dba-b62e-4d60-8cc4-599be46021e1

Source: BioNinja

Additionally, the RNA World Hypothesis also offers explanations for how the first self-replicating RNA molecules could have formed. It proposes that RNA could have formed through the gradual in the presence of suitable catalysts, such as and other inorganic catalysts. 🧱

Key Terms to Review (21)

Origin of Life on Earth

: The origin of life on Earth refers to the process and timeline by which life first emerged on our planet, a subject of ongoing scientific research. It is generally accepted that this occurred around 3.9 billion years ago.

Abiogenesis

: Abiogenesis is the process by which life arises naturally from non-living matter, such as simple organic compounds.

Fossilized Stromatolites

: Fossilized stromatolites are layered rock formations created by the growth of microorganisms, particularly cyanobacteria. They are some of the oldest known fossils on Earth, dating back over 3.5 billion years.

Panspermia

: Panspermia is the hypothesis that life exists throughout the Universe, distributed by space dust, meteoroids, asteroids, comets, planetoids and also by spacecraft carrying unintended contamination by microorganisms.

Atmospheric Oxygen (O2)

: Atmospheric oxygen refers to the oxygen present in Earth's atmosphere. It makes up about 21% of our atmosphere and is essential for aerobic respiration in many organisms.

Primitive Earth Model

: The primitive earth model is a scientific theory that describes the conditions and environment of early Earth, around 4.5 billion years ago.

Amino Acids

: Amino acids are organic compounds that combine to form proteins. They are fundamental building blocks of life and necessary for numerous bodily functions.

Nucleotides

: Nucleotides are the building blocks of nucleic acids like DNA and RNA. Each nucleotide is composed of a sugar, a phosphate group, and a nitrogenous base.

Meteorites

: Meteorites are pieces of rock or metal from space that have survived their journey through Earth's atmosphere and landed on our planet's surface.

Chemical Experiments

: Chemical experiments involve combining or manipulating substances to observe the resulting chemical reactions, often to test a hypothesis or understand a chemical process.

Inorganic Precursors

: These are simple compounds, often containing elements like carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur, which participate in chemical reactions to form more complex molecules.

Organic Molecules or Monomers

: These are small molecules that can join together with other similar molecules to form larger structures known as polymers. They contain carbon atoms and are often found in living organisms.

Polymers

: Large molecules made from many smaller units called monomers linked together in a chain. Examples include proteins (polymers of amino acids), DNA (polymers of nucleotides), and polysaccharides (polymers of sugars).

DNA and RNA

: DNA (Deoxyribonucleic Acid) is a molecule that carries most of the genetic instructions used in growth, development, functioning and reproduction. RNA (Ribonucleic Acid) plays crucial roles in coding, decoding, regulation and expression of genes.

Enzymes

: Enzymes are biological catalysts that speed up chemical reactions in living organisms without being consumed in the process.

Nucleic Acids

: Nucleic acids are large biomolecules essential for all known forms of life. They carry genetic information and include DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).

Self-Replicating Entities

: These are entities that can make copies of themselves. In biology, this often refers to molecules such as DNA and RNA.

Peptide Bonds

: A peptide bond is a chemical bond formed between two amino acids when the carboxyl group of one reacts with the amino group of another, releasing water (a dehydration reaction).

Synthesis of Sugars

: This refers to how living organisms create simple sugars like glucose from non-carbohydrate precursors through processes like photosynthesis or gluconeogenesis.

Clay Minerals

: A group of hydrous aluminium phyllosilicates minerals that may contain minor amounts of other elements such as potassium, magnesium iron etc., typically formed over long periods through weathering processes.

Polymerization of Nucleotides

: The process by which nucleotides (the building blocks of DNA and RNA) are linked together to form a long chain, or polymer.