00:00Have you ever looked up into the night sky and wondered how we got here?
00:04With over 100 billion Earth-like planets out there in the Milky Way,
00:08it seems almost arrogant to think that we are alone in the universe.
00:12But at the same time, scientists have been unable to find any real proof of life elsewhere,
00:18making the question of how life began on Earth one of the biggest unsolved mysteries in science.
00:25In today's video, we're going to discuss the most popular scientific theories
00:30that try to answer the question of how life began on our planet.
00:33What scientists do know is that the Earth has existed for about 4.5 billion years,
00:39but life didn't appear until about 3.8 billion years ago.
00:43This means that life on Earth started pretty dang quickly after the planet formed.
00:47So without further ado, let's jump into it.
00:52Panspermia
00:52One of the more popular theories is called panspermia,
00:57which proposes that life did not originate on Earth,
01:00but was instead brought here from somewhere else in outer space.
01:04While this may sound like a crazy theory,
01:06it is actually supported by some pretty big names in science.
01:10Both Carl Sagan and Sir Fred Hoyle were proponents of the theory,
01:14with Hoyle even coining the phrase,
01:17We are all Martians.
01:19To be fair, they weren't referring to the little green men
01:22that animate Mars in our collective imagination,
01:25but rather to the idea that life originated on Mars.
01:29More recently, scientists have suggested that life may have originated in interstellar space itself.
01:35This idea is based on the discovery of organic molecules in space,
01:39including amino acids, which are the building blocks of proteins.
01:43These molecules are essential for life as we know it,
01:46and their presence in space suggests that they could have played a role in the origin of life on Earth.
01:53One way these molecules could have made their way to Earth is through meteorites.
01:58Meteorites are fragments of rocks that have broken off from other planets or larger bodies in space
02:04and crashed into Earth.
02:07Scientists have found evidence of organic molecules in some meteorites,
02:11suggesting that they could have delivered the building blocks of life to our planet.
02:16Another way that organic molecules could have arrived on Earth is through comets.
02:21Comets are icy bodies that travel around the sun in highly elliptical orbits,
02:26and some of them pass close enough to Earth to deliver their icy contents to our atmosphere.
02:31In 1986, the first unambiguously interstellar object, namely Comet Halley, was discovered.
02:39And since then, many more have been discovered, such as Comet 81P,
02:45which is one of the most frequently observed comets in history.
02:49In 2018, scientists analyzed the composition of Comet 81P
02:55and found that it contained a variety of organic molecules,
02:59including methane, ethane, propane, butane, and hydrogen cyanide.
03:05While this is circumstantial evidence that comets could have delivered organic molecules to Earth,
03:10it doesn't necessarily prove that they did.
03:13The molecules could have formed on the comet as a result of reactions
03:17between the solar wind and the surface ices, rather than being delivered to Earth.
03:22Further research will be needed to determine whether comets really did play a role in the origin of life.
03:28The RNA World Hypothesis
03:32Another popular theory is called the RNA World Hypothesis.
03:37This theory proposes that RNA, not DNA, was the primary genetic material in early life forms.
03:44Unlike DNA, which is double-stranded, RNA is single-stranded.
03:48However, RNA can still store genetic information, and it can also catalyze chemical reactions,
03:56making it a good candidate for the molecule that gave rise to life on Earth.
04:00Proponents of the RNA World Hypothesis believe that RNA molecules could have replicated themselves
04:07and carried out the functions of life before DNA and proteins evolved.
04:11One piece of evidence in favor of the RNA World Hypothesis is that all living cells on Earth
04:18use RNA as an intermediate in the process of protein synthesis.
04:23This suggests that RNA may have had a similar role in early life forms.
04:28Another piece of evidence is that some viruses use RNA as their genetic material,
04:33which supports the idea that RNA was the primary genetic material in early life.
04:38The RNA World Hypothesis is still controversial, however,
04:43because it is unclear how RNA could have arisen on its own.
04:47It is possible that RNA may have been synthesized abiotically under early Earth conditions.
04:53This is supported by the fact that several groups of researchers have been able to synthesize
04:58RNA molecules in the laboratory using conditions that mimic those on early Earth.
05:04However, other scientists argue that the synthesis of RNA
05:07is unlikely to have occurred on early Earth and that DNA was probably involved in the process.
05:14More research is needed to resolve this controversy
05:16and determine whether RNA really was the primary genetic material in early life.
05:22The Metabolism First Hypothesis
05:25A more recent development in our understanding of the origins of life on Earth
05:29has led scientists to propose that metabolism may have preceded both RNA and DNA in the development of life.
05:37This idea is known as the Metabolism First Hypothesis.
05:41According to this hypothesis, self-sustaining networks of interacting chemical species
05:46could have predated both RNA and DNA and provided the foundation for the origin of life.
05:53These networks would have been open systems,
05:55meaning that they would have exchanged materials with their environment
05:58and used energy to maintain their organization.
06:02One of the main advantages of the Metabolism First Hypothesis
06:05is that it does not rely on the formation of complex biomolecules such as RNA or DNA.
06:12These molecules are difficult to synthesize abiotically
06:15and it is unclear how they could have arisen on early Earth.
06:19On the other hand, the Metabolism First Hypothesis focuses on the interactions between chemical species
06:26which are easier to study and more amenable to experimental investigation.
06:33For example, researchers have been able to create self-organizing lipid membranes
06:38in the laboratory that resemble the cell membranes of modern cells.
06:42These membranes are formed by amphipathic molecules
06:45which have both hydrophilic, water-loving, and hydrophobic, water-fearing regions.
06:52The hydrophilic regions of the molecules interact with water
06:56and the hydrophobic regions cluster together to avoid water.
07:01This self-assembly of amphipathic molecules into membranes
07:05is a key feature of the Metabolism First Hypothesis.
07:09While the Metabolism First Hypothesis is still in its early stages,
07:13it offers a promising new approach to understanding the origin of life.
07:20By focusing on the interactions between chemical species,
07:23this hypothesis may help scientists unravel the mystery of how life arose on Earth.
07:30Deep Sea Vent Theory
07:31Lastly, we're going to look at the Deep Sea Vent Theory,
07:36which proposes that life on Earth originated in the deep sea, near hydrothermal vents.
07:41These are openings in the seafloor that release hot water and minerals from the Earth's interior.
07:48The water that comes out of these vents is often rich in chemicals that can support life,
07:53such as methane and hydrogen sulfide.
07:55The chemicals are produced by the breakdown of rocks and minerals in the Earth's crust.
08:00Hydrothermal vents were first discovered in the 1970s,
08:04and since then scientists have found that they support a variety of unique ecosystems.
08:09The organisms that live near hydrothermal vents are called extremophiles,
08:15and they are able to survive in extremely hot, high-pressure environments that are devoid of oxygen.
08:21While these organisms are not directly related to the origin of life,
08:25they do suggest that life could have arisen in similar environments on early Earth.
08:30Proponents of the Deep Sea Vent Theory believe that the chemicals released by these vents
08:35provided the energy and building blocks provided the energy and building blocks for the origin of life.
08:39One piece of evidence in support of this theory is that hydrothermal vents are a rich source of methane and hydrogen sulfide,
08:48which are potential sources of energy for early life forms.
08:52Another piece of evidence is that the minerals released by these vents
08:56could have provided the surface on which early life forms could have assembled.
09:00However, there are also some criticisms of the Deep Sea Vent Theory.
09:04For example, the temperatures near hydrothermal vents are often too high for the kinds of molecules
09:10that are necessary for life as we know it to exist.
09:14Additionally, the lack of oxygen in these environments makes it unlikely that photosynthesis could have evolved,
09:21which means that any life forms near hydrothermal vents would have been limited to chemotrophs.
09:27Chemotrophs are organisms that get their energy from the oxidation of inorganic compounds.
09:34While chemotrophs are found in modern ecosystems,
09:36they are not thought to have been major contributors to the evolution of life on Earth.
09:41Despite these criticisms, the Deep Sea Vent Theory remains an intriguing possibility
09:46for how life could have originated on our planet.
09:49So what do we really know?
09:51While the question of how life began on Earth is still a mystery,
09:55scientists have made significant progress in understanding the conditions that may have led to the origin of life.
10:02We know that life on Earth started pretty quickly after the planet formed,
10:06and we also know that early life forms were likely very different from the organisms we see today.
10:11Theories such as the RNA World Hypothesis and the Metabolism First Hypothesis
10:16provide possible answers to the question of how life may have begun.
10:20And while there is still much that we don't understand,
10:24each new discovery brings us closer to solving this age-old mystery.
10:28What do you think about the theories presented in this video?
10:32Do you think life originated on Earth,
10:34or was it brought here from somewhere else in the universe?
10:38Let us know your thoughts in the comments below.
10:41And don't forget to like and subscribe so you never miss an episode of our channel.
10:45Thanks for watching and we'll see you next time.
10:47We'll see you next time.
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