The idea that life did not originate on earth егэ

1 The idea that life did not originate on Earth, but was carried here either deliberately or by natural processes, has its roots at least as far back as the ancient Greeks. This idea, often referred to as panspermia, took on a scientific form in the work of various nineteenth-century authors. It later gained widespread popular appeal through the work of the Swedish chemist Svante Arrhenius, who argued that spores of life could survive in space and travel between star systems through the pressure of solar radiation.

2 The panspermia hypothesis eventually fell out of favor for a variety of reasons. Skeptics pointed out that microorganisms could not possibly survive the damage caused by ultraviolet radiation and cosmic rays while being propelled out of a solar system away from a star. Indeed, it was unclear how biological material could escape from a planet by natural processes in the first place. If unprotected, the molecules of life would quickly be destroyed by radiation near the ejecting planet. Furthermore, it was not clear how microorganisms, having made a journey across the huge distances of interstellar space, could have safely descended to the surface of the Earth or any other planet. Arrhenius himself argued that organisms caught inside meteorites would be subjected to incandescent* temperatures while entering the atmosphere of a terrestrial body. Such heat would destroy any life-forms lucky enough to have survived to this point.

3 Despite the seeming implausibility* of the panspermia hypothesis, some theorists have resurrected the notion in recent decades since laboratory research has shown that many of the objections to the hypothesis can be overcome. Scientists have shown that microorganisms protected from radiation by grains of material could be ejected from a solar system if the repulsive force (p) of the ejecting star is greater than the attractive force (g) of the star’s gravity. Such ejecting stars cannot be too luminous since brighter stars emit too much ultraviolet radiation for the survival of bacteria. Organisms can only enter new solar systems whose stars’ p/g ratio is low. thus allowing the gravity to pull the microbes into the planetary orbits. According to some researchers, material ejected from a planetary system could also eventually become part of an interstellar molecular cloud, which eventually produces a new planetary system as well as a large number of comets. Comets can retain microorganisms protected by other material and water, and impact onto new planets, which by then would have cooled sufficiently for the life in the grains to take hold.

4 Further supporting evidence about the likelihood of survival of bacteria traveling through space and entering a planetary atmosphere has been gained from studies of a meteorite of Martian origin found in Antarctica in 1984. Whether or not the meteorite contains fossils of Martian bacteria (and many researchers now seem to reject this possibility), microscopic studies of its internal structure have shown that the interior was not heated to more than 40 degrees Celsius since before leaving the Martian surface. In other words, neither the original impact that must have ejected the rock away from the Martian surface nor the heat generated by its entry into the Earth’s atmosphere did, in fact, melt or vaporize the internal portions of the meteorite. So it is quite possible that any life-form that had undergone such a trip would survive. As for the long journey itself, experiments aboard a European Space Agency mission have shown that bacterial spores can survive in deep space for at least five years. This is sufficient time for viable interplanetary travel, although not, of course, for interstellar travel.

5 Today, the panspermia hypothesis is being regarded with less skepticism than formerly. Although the orthodox view is still that life evolved on Earth (and possibly other planets in the universe) without extraterrestrial input, more and more research is pointing to the feasibility of some form of interstellar «seeding.» Wickramasinghe and Hoyle, who championed the hypothesis of the interstellar transmission of life during the 1970s, argued persuasively that prebiotic chemicals have been shown to exist by remote sensing data of Comet Halley. Furthermore, they point out that evidence for viable microorganisms existing in comets could be attained in the near future if unmanned space missions could capture and return to Earth with cometary material.

Questions

1 Early supporters of the panspermia hypothesis
A  rejected the main elements of the hypothesis
B  argued that some primitive life has been detected on a comet
C  pointed out that space missions will find life elsewhere
D suggested that the «seeds» of life may have been deliberately planted

2. The word «propelled» in the paragraph 2 is closest in meaning to
A  rejected
B plunged
C  heaved
D thrust

3. According to the passage, the panspermia hypothesis fell out of favor for all of the following reasons EXCEPT
A  the potential damage caused by ultraviolet radiation
B  the unlikelihood of natural processes leading to the ejection of biological material
C  the probability that heat would destroy incoming life-forms
D knowledge that life can’t exist elsewhere in the universe

4. The word “resurrected» in the paragraph 3 is closest in meaning to
A destroyed
B  reintroduced
C initiated
D succeeded

5. The word “ retain” in the paragraph 3  is closest in meaning to
A prevent
B erode
С avert
D keep

6. According to the passage, the panspermia hypothesis is
A of historical interest only
B being taken seriously again
C not really good science
D probably true

 7. The word «its» in the paragraph 4 refers to
A  the Martian
B  the bacteria
С  the meteorite
D the interior

8 The phrase “such a trip” in the paragraph 4 refers to
A a journey from Mars to Earth
B the descent through Earth’s atmosphere
C a trip from another solar system
D interstellar traveling

9. According to the passage, the meteorite found in Antarctica
A does not contain bacteria fossils
B  might contain bacteria fossils
C  has fossils originating on Earth
D could not originate from Mars

10. Which of the sentences below best expresses the essential information in the highlighted sentence in the paragraph 5? Incorrect choices change the meaning in important ways or leave out essential information,
A Nowadays, the panspermia hypothesis has been more or less rejected.
B Currently, the panspermia hypothesis is looked on with more astonishment than previously.
C These days, the panspermia hypothesis is judged more plausible than before.
D The modem scientific establishment now generally accepts the validity of the panspermia hypothesis.

11. Look at the four letters A, B, C, D that indicate where the following sentence could be added to the passage.

However, even if organisms were somehow shielded inside fine grains of carbon they would be too heavy to be ejected from a planetary system by the pressure of radiation.

Where would the sentence best fit?

The panspermia hypothesis eventually fell out of favor for a variety of reasons. A__________ Skeptics pointed out that microorganisms could not possibly survive the damage caused by ultraviolet radiation and cosmic rays while being propelled out of a solar system away from a star. Indeed, it was unclear how biological material could escape from a planet by natural processes in the first place. В_____________ If  unprotected, the molecules of life would quickly be destroyed by radiation near the ejecting planet. C______________ Furthermore, it was not clear how microorganisms, having made a journey across the huge distances of interstellar space, could have safely descended to the surface of the Earth or any other planet. D__________ Arrhenius himself argued that organisms caught inside meteorites would be subjected to incandescent’ temperatures while entering the atmosphere of a terrestrial body. Such heat would destroy any life-forms lucky enough to have survived to this point

Cambridge Preparation to the TOEFL Practice Tests

Panspermia

The idea that life did not originate on Earth, but was carried here either deliberately or by natural processes, has its roots at least as far back as the ancient Greeks. This idea, often referred to as panspermia, took on a scientific form in the work of various nineteenth-century authors. It later gained widespread popular appeal through the work of the Swedish chemist Svante Arrhenius, who argued that spores of life could survive in space and travel between star systems through the pressure of solar radiation.
The panspermia hypothesis eventually fell out of favor for a variety of reasons. Skeptics pointed out that microorganisms could not possibly survive the damage caused by ultraviolet radiation and cosmic rays while being propelled out of a solar system away from a star. Indeed, it was unclear how biological material could escape from a planet by natural processes in the first place. If unprotected, the molecules of life would quickly be destroyed by radiation near the ejecting planet. Furthermore, it was not clear how microorganisms, having made a journey across the huge distances of interstellar space, could have safely descended to the surface of the Earth or any other planet. Arrhenius himself argued that organisms caught inside meteorites would be subjected to incandescent* temperatures while entering the atmosphere of a terrestrial body. Such heat would destroy any life-forms lucky enough to have survived to this point.
Despite the seeming implausibility* of the panspermia hypothesis, some theorists have resurrected the notion in recent decades since laboratory research has shown that many of the objections to the hypothesis can be overcome. Scientists have shown that microorganisms protected from radiation by grains of material could be ejected from a solar system if the repulsive force (p) of the ejecting star is greater than the attractive force (g) of the star’s gravity. Such ejecting stars cannot be too luminous since brighter stars emit too much ultraviolet radiation for the survival of bacteria. Organisms can only enter new solar systems whose stars’ p/g ratio is low, thus allowing the gravity to pull the microbes into the planetary orbits. According to some researchers, material ejected from a planetary system could also eventually become part of an interstellar molecular cloud, which eventually produces a new planetary system as well as a large number of comets. Comets can retain microorganisms protected by other material and water, and impact onto new planets, which by then would have cooled sufficiently for the life in the grains to take hold.
Further supporting evidence about the likelihood of survival of bacteria traveling through space and entering a planetary atmosphere has been gained from studies of a meteorite of Martian origin found in Antarctica in 1984. Whether or not the meteorite contains fossils of Martian bacteria (and many researchers now seem to reject this possibility), microscopic studies of its internal structure have shown that the interior was not heated to more than 40 degrees Celsius since before leaving the Martian surface. In other words, neither the original impact that must have ejected the rock away from the Martian surface nor the heat generated by its entry into the Earth’s atmosphere did, in fact, melt or vaporize the internal portions of the meteorite. So it is quite possible that any life-form that had undergone such a trip would survive. As for the long journey itself, experiments aboard a European Space Agency mission have shown that bacterial spores can survive in deep space for at least five years. This is sufficient time for viable interplanetary travel, although not, of course, for interstellar travel.
Today, the panspermia hypothesis is being regarded with less skepticism than formerly. Although the orthodox view is still that life evolved on Earth (and possibly other planets in the universe) without extraterrestrial input, more and more research is pointing to the feasibility of some form of interstellar «seeding». Wickramasinghe and Hoyle, who championed the hypothesis of the interstellar transmission of life during the 1970s, argued persuasively that prebiotic chemicals have been shown to exist by remote sensing data of Comet Halley. Furthermore, they point out that evidence for viable microorganisms existing in comets could be attained in the near future if unmanned space missions could capture and return to Earth with cometary material.

*incandescent: producing a bright light after being heated to a high temperature
*implausibility: the condition of being difficult to believe

Questions 13-25

Ocean Energy Systems

In recent years, the oceans have been seen as a potential source of energy. Oceans are huge reservoirs of renewable energy, which have yet to be properly harnessed*. Some estimates say that during the second decade of this century, ocean energy sources will generate more than 1,000 megawatts of electricity, which is enough to power a million homes in the industrialized world. Several technologies have been developed for exploiting these resources in a practical way, among which ocean thermal energy conversion (OTEC) is one of the most promising. Experimental OTEC plants have been constructed using different operating principles, although as yet no large-scale commercially viable plant has been launched.
The basic operation behind this system uses the heat energy stored in the oceans as a source of power. The plant exploits the difference in water temperature between the warm surface waters heated by the sun and the colder waters found at ocean depths. A minimum temperature difference of 20 degrees Celsius between surface and depth is required for efficient operation, and this situation is typically found only in tropical and subtropical regions of the world. There are two basic kinds of OTEC system: the open cycle system and the closed cycle system. In the open cycle system, the warm surface water is converted into steam in a partial vacuum and this steam drives a turbine connected to an electrical generator. In a closed cycle system, the warm surface water is used to boil a fluid, such as ammonia, which has a low boiling point. In both systems cold water pumped up from the ocean depths condenses the vapor. In the open system, the steam is condensed back into a liquid by cold water pumped from deep-ocean water and then discharged. In the closed system, the condensed ammonia is used to repeat the cycle continuously. Various hybrid systems using characteristics of both open and closed cycle plants have also been designed.
The OTEC system is potentially an important source of clean, renewable energy, which could significantly reduce our reliance on fossil fuels and nuclear fission. Unlike other forms of renewable energy, such as those provided directly by the sun and wind, OTEC plants can generate power 24 hours per day, 365 days per year. Furthermore, the design of this technology avoids any significant release of carbon dioxide into the atmosphere. OTEC can offer other important benefits apart from power production. Aquaculture is one important spinoff. It may also be economically feasible to extract minerals from the pumped seawater. Freshwater for drinking and irrigation is another by-product, and this will be an important advantage in regions where freshwater is limited.
Some drawbacks to this form of power generation have been noted. Perhaps the biggest drawback at present is the high capital cost of initial construction due mainly to the expense of the large pipeline used to pump water from 1,000 meters below the surface. Furthermore, the conversion of thermal to electrical energy in the OTEC system works at very low efficiency, which means that these plants will have to use a lot of water to generate practical amounts for the power grid. For this reason, the net power output is reduced, since a significant portion of the output must be used to pump water. There are also potential ecological drawbacks, since the water discharges will change the water temperature and disturb some marine habitats. This impact could, however, be minimized if the water is discharged at greater depths.
The main obstacle created by high initial expenses will have to be met before OTEC competes with conventional alternatives, and until such time, OTEC will remain restricted to experimental plants. When technology permits lower start-up costs, this technology will make an important contribution to world energy requirements.

*harnessed: controlled for use

Questions 26-39

Neolithic Agriculture Development

In the Neolithic period, starting around 10,000 years ago, perhaps the most important economic revolution in human history occurred — the commencement of agriculture and the domestication of animals for human consumption. From this point in time, people could start to rely on a more consistent and much increased food supply. As a corollary of this, considerably larger populations could be supported and people could settle in one place without the need to migrate in search of food supplies. Equally important, the surpluses of crops and animals meant that not all the population needed to dedicate their time and energy to farming; some could now learn specialized skills such as crafts or trade. The building of permanent settlements where skills could be developed brought about the conditions necessary for the first growth of towns. But several thousand years elapsed between the beginnings of agriculture and the rise of what we call civilization about 6,000 years ago.
Recent evidence seems to indicate that while the Neolithic revolution first took place in the Middle East — in the valleys of the Tigris-Euphrates and of the Nile — it occurred independently in other areas of the world. The origins of the revolution are not known in great detail, but it is known that the wild grasses that were the ancestors of wheat and barley grew natively in the Eastern Mediterranean area. It may be that Mesolithic (Middle Stone Age) foragers* simply supplemented their diet by reaping these wild grasses, and later came to understand the advantage of returning some of the grain to the soil as seed. Whatever the case, we know that at an early date people living in the Eastern Mediterranean region, who lived by hunting, fishing, and gathering, began to make sickles, with stone teeth set in bone handles. Such tools were certainly used for reaping some grass crop, whether cultivated or wild.
Around this time, other communities in the Middle East cultivated plants from which they learned how to obtain flour. Evidence shows that they ground down the grain with a simple type of mill, consisting of a large saddle-shaped stone on which a smaller stone was rubbed up and down. The livestock they bred — cattle, sheep, pigs, and goats — was exploited for their meat, skins, and milk.
Both in Egypt and Mesopotamia, the periodic floods of great rivers such as the Nile and the Tigris-Euphrates not only supplied water to the fields but also brought down fresh soil in the form of fertile muddy sediments. This sediment was deposited on flood plains around such rivers, thus annually restoring the fruitfulness of the land. This regular flooding and sediment deposit allowed these early farmers to continue cultivating the same fields repeatedly for generations without exhausting the fertility of the soil, and crop surpluses were, therefore, available to allow an increase in population and a growth in trade and skills development. The area available for cultivation was expanded when people learned to draw off the river water into man-made irrigation canals and ditches, watering and fertilizing larger and larger areas of land.
The practice of artificial irrigation affected the soil in various ways, but not always for the good. Since the channels were often shallow, there was frequently a great loss of water through evaporation in a hot climate. This could lead to a marked increase in soil salinity. since the salts held in solution or suspension were deposited as the water evaporated, and too much salinity could eventually damage the soil. But overall the effect of the irrigation system was to create an artificial environment — and to some extent an artificial climate — with a range of conditions that favored both human experiment and agricultural development. Beyond this, settled agriculture led to the development of property rights and hence to a legal framework and mechanisms to enforce laws. This in turn led to a more extensive and hierarchical government organization and hence to the development of large, stable communities.

*foragers: people who go searching for food

For almost seven years, NASA’s Curiosity rover has been exploring the terrain of Mars. Two weeks ago, it made a stunning discovery: relatively large concentrations of methane gas. The rover also found methane in 2013, but the readings recorded this month—approximately twenty-one parts per billion—were about three times as concentrated. The reason this news registered among scientists is that methane is often a sign of life; although the gas can be produced by various chemical reactions, most of it comes from animate beings. Does this mean that we are on the verge of discovering life on Mars, and, if so, what kind of life is it likely to be?

To discuss these questions, I spoke by phone with Gary Ruvkun, a molecular biologist and professor of genetics at Harvard Medical School. Ruvkun has what he admits are somewhat unusual opinions about life’s origins, and about the possibility of finding life elsewhere. In short, he questions the common assumption that our form of DNA-based life began on Earth. What began as an interview about the methane discovery turned into a discussion about why he wants to send something called a DNA sequencer to Mars. (After our conversation, NASA announced that the methane concentrations had descended back to their usual levels, further confounding scientists.) During our conversation, which has been edited for length and clarity, we also discussed the ways in which scientific debates about the origins of life intersect with religious ones, the reasons he might be dead wrong, and what it feels like to hold a minority opinion in the scientific community.

What is your biggest takeaway from this methane discovery?

Looking for methane is a good method to indirectly look for life. The problem is, there are chemical ways to make methane as well. It is not a perfect surrogate for life. So the way most life-detection experiments are proposed from NASA, especially in this era of exoplanets, where so many planets have been detected around stars, is to do spectroscopic studies of their atmosphere. It is always involving abundant chemicals, like methane and CO₂.

Do you think that’s the best way to do it? Or are you suggesting that there’s a better way to do them?

It’s the only way to do it with things that are far away. My favorite way to look for life is to go to a planet and look for DNA. And that assumes that life on another planet would be exactly like life here, which is not how most astrobiologists think about things.

How do you think differently about it?

I think viewing life as having started here is a little bit presumptuous. It seems we’re very, very, very special and it all happened here. I find the idea aesthetically appealing that life as we know it is universal across the Milky Way. It just seems like, once it evolves, it spreads. And one way to argue this is running the clock forward instead of running it in reverse. If we’re really talking about colonizing Mars, step one is to send bacteria to Mars to generate an atmosphere. So if you run the clock forward a million years, presumably, we will be sending bacteria to planets a million light years from us.

O.K., wait, I just want to understand this. So what you’re saying is that you find romantic or nice the idea that other life forms would be like us?

Yeah. That life didn’t start here. It just landed here. That it came from somewhere else. And a lot of people complain about that. They say, “Well, then you’re just putting the problem of origin of life somewhere else.” Which is true.

In an e-mail to me, you referred to your views as “not very standard for microbiology.” And this is partly because you want to send a DNA sequencer to Mars, yes?

Here on Earth, if you go to some lake or a forest and want to know who lives there, the current method of choice for figuring out who’s there is to just take dirt, make DNA, and do all the genome sequences inside that DNA. And you get a pretty good fingerprint of who lives there. And of course there’s a lot of different kinds of bacteria that live in soils and things like that.

And, if you look in the literature, there are tens of thousands of papers now that do that, and it was done the first time maybe twenty years ago, using DNA as a kind of signature to look for living things. So we would say, “We’ll just do that on Mars and do the sequence.” And you could ask, “Well, do you find anything there that looks like it’s our cousin?” It doesn’t have to be our brother. It can just be more distantly related than a brother, but a cousin, and therefore coming from the same tree of life. Once you do that, you can say, “Oh, well, life on Earth and Mars is similar, and that’s sort of the least-interesting idea, because Earth and Mars are right next to each other.” So it’s kind of almost obvious that they would share the same kind of life, because there’s an exchange. But what if it actually is the entire Milky Way that has the same life?

What would people who are skeptical of the way you’re thinking about it say in response to this?

They’d say that’s just stupid. [Laughs.] Because they’re saying, “Well, it had to start somewhere, and so why would you not think it started here? Why are you positing that we caught life instead of evolved it?” Because there’s clearly evidence for how life evolved in our genomes. It’s what’s called the RNA World, which was kind of the earliest form of life, and is still present in our genomes. We can see it there, and so you can discern early steps in evolution just by looking in modern genomes. In orthodoxy and all the textbooks, the RNA World—that’s kind of the precursor to the DNA world—was here on Earth four billion years ago. And I would propose, no, it was probably ten billion years ago, somewhere on the other side of the Milky Way, and it’s been spreading all across the Milky Way.

So the four-billion-year and the ten-billion-year estimates—there is no scientific basis for either estimate? Is that what you are saying?

No, no, no. The Earth is 4.5 billion years old. And the universe, at least based on estimates from the Big Bang, is something like fourteen billion years. So, if life evolved somewhere else, that buys you about ten billion years of time. But I’d rather it bought you a hundred billion years of time or a thousand billion years of time. That would be more satisfying.

Why would it be more satisfying?

Well, because it allows more time. See, the thing is, if you look in the fossil record, where’s the first evidence of life? Well, you can see evidence of bacterial life, things that look like bacteria, the things that are called stromatolites, which are a kind of blue-green algae bacteria that live in colonies. Those things form good fossils, and you can see those about three and a half billion years ago. So, life had already evolved to the point of there being pretty complicated bacteria very quickly, after the Earth cooled.

One of the most frequently asked questions in any scientific, philosophical, or theological debate is – where did life on Earth come from? Scientists already know a great deal about how life on Earth came to be as it is today. There’s physical evidence all around showing how life has evolved and changed over the millennia of Earth’s existence. 

We know much less about the first life on Earth. So what was the first living thing from which all other life on Earth originates, and how did it come to be alive? 

Panspermia is the theory that life on Earth originated on another planet altogether and was deposited on Earth due to a meteor impact. If this sounds unreasonable, like something out of a superhero comic book, that’s understandable. However, science has long laughed off this possibility as a stretch at best.

However, recent scientific advances in understanding what “life” actually means have revived the debate about the Panspermia theory. There’s still a long way to go before this theory will be considered scientifically likely. But it appears that the possibility of organisms on Earth have originated on other planets holds more water than you may think.

The Birth Of Our Solar System

The planet we know today as Earth wasn’t always the same as it is today. Yes, there was Pangaea, and the dinosaurs, and single-celled organisms in the ocean. But before that, Earth was just a hot, dead rock in space continuously blasted with cosmic debris. 

If we go back just a little bit further, it wasn’t even a solid rock. Our entire solar system was just a giant, swirling dust cloud. Scientists are still far from certain what happened, but something disturbed the dust cloud enough to make it start to pull together.

The pulling together of dust on a cosmic scale caused it to swirl so quickly that it began to generate its own gravity. As a result, hydrogen protons fused, producing helium and releasing massive amounts of energy that would eventually become our Sun. That was 4.6 billion years ago. 

Over the next 100 million years, all the matter in the solar system that wasn’t consumed in the formation of the Sun kept swirling. Over time, it collected into the larger and larger masses that eventually became Earth and the other planets of our solar system. 

Conditions For Life

Even then, though, Earth was just a hot rock hurtling through space around the Sun under constant meteor bombardment. The hot magma that made up Earth’s surface began to cool and sink, forming the molten core and the oceans. Then a massive meteor impact around 4.5 billion years ago formed our Moon, beginning Earth’s journey toward habitability. 

Scientists now believe that Mars, on the other hand, was once more habitable than Earth in its pre-Moon days. So while science has yet to definitively prove the current or former existence of native Martian life, we do know that the right conditions for life may once have existed there.

Early Life On Earth

Meanwhile, life appeared and evolved so rapidly on Earth that scientists are still trying to figure out how it happened. We don’t yet know when or how life on Earth began. But we know that there are signs of life on Earth 3.8 billion years ago and definitive proof of life as early as 3.5 billion years ago.

What’s fascinating is that the building blocks of this early life on Earth are the same ones that make up all known life today – DNA and RNA. So some scientists today believe that the rapid appearance of these molecules on Earth can mean one of two things.

First, it could mean that life on Earth evolved more rapidly in the early years than it has across recorded time. However, the alternate theory is that life on Earth had such a complex molecular structure because it had already evolved elsewhere – on another planet.

Seeding Earth

We’re not talking about Superman arriving from Krypton in a small spaceship. Instead, the Panspermia theory posits that a meteor blast from a nearby planet may have launched space debris into Earth’s atmosphere. This debris, some scientists believe, may have carried with it microscopic life forms that, against all odds, survived and thrived on Earth.

The most likely origin for pre-evolved life forms is Mars, which is now believed to have previously been habitable. According to the Panspermia theory, Mars was not only habitable but sustained life during a period that overlapped with Earth’s early days of habitability.

If a meteor struck Mars with enough force, such as the force of the meteor that struck Earth forming the Moon, it might have caused Martian debris to fly into space. Martian microorganisms living in that space debris may have survived the journey, landing on Earth and taking root on its newly habitable surface.

Could Panspermia Theory Be True?

It may seem a little far-fetched to think that a space rock hitting the surface of Mars could send Martian life hurtling toward Earth. However, the minimum distance between Mars and Earth, even when their orbits are nearest, is 33.9 million miles. So is it possible for Martian space debris to travel that far?

Earth’s surface is littered with craters from massive meteor impacts. Around 2.2 billion years ago, a meteor larger than South Africa’s Table Mountain collided with Earth, leaving an impact crater that scientists believe was once over 185 miles across. And 65 million years ago, Earth was struck by a massive meteor that wiped out the dinosaurs and left a crater 150 miles wide.

That kind of cosmic impact is almost impossible to fathom, as we have no natural frame of reference to compare that amount of force to. But we do know that Martian planetary material has been found on Earth’s surface. So not only could it happen – it has happened. 

Could an organism survive the journey?

Even if a blob of planetary material carrying a Martian microorganism could make its way from Mars to Earth, how could that tiny creature survive the extreme journey? It seems implausible between the vacuum of space, the solar radiation, and the force and heat of the impact itself.

However, there are already organisms on Earth that have proven themselves capable of surviving these extremes. For example, tardigrades, sometimes called “water bears,” are tiny eight-legged micro animals that can survive at temperatures from absolute zero to boiling, under six times the pressure of the deepest ocean, and in the vacuum of space. 

They can also dehydrate themselves and go dormant indefinitely, a process called cryptobiosis. They do this to survive excessively dry climates, and when conditions improve, they rehydrate themselves and go on as though nothing happened. 

Even simpler organisms like bacteria could survive all extreme conditions and live inside a rock for years. Scientists believe that a one-millimeter colony of bacteria could survive unsupported in space for up to eight years. So we already know of life on Earth capable of surviving an unprotected journey on a rock from Mars. We just haven’t proven that it’s happened.

Potential Alien Animals

Aside from the fact that Martian life could have hitched a slingshot ride on a rock hurtling toward Earth, some scientists believe they’ve found proof of those alien origins. Cephalopods, particularly the octopus, feature traits and adaptations that appear out of nowhere on the evolutionary timeline.

Instantaneous camouflage, camera-like eyes, physical flexibility, and complex intelligence all evolved in cephalopods in a way that scientists haven’t found in any other life form. In addition, the octopus genome is staggeringly complex, with 33,000 more protein-coding genes than humans.

One scientist described the octopus genome as so complex that it could have “futuristic” origins. Some argue that Panspermia is one possible explanation for such an advanced state of evolution. Specifically, some scientists believe it’s possible that cephalopods evolved on some other planet and arrived on Earth as cryopreserved eggs.

Diversity Of Life On Earth

Now, evolution is a complex process that science is still trying to understand. Just because other species haven’t developed the same evolutionary advantages as the octopus doesn’t necessarily mean those advantages have alien origins. 

But our planet is covered in diverse plant and animal life, and scientists are still discovering strange and unfathomable creatures in Earth’s oceans. Without a clear evolutionary bread crumb trail to explain them, scientists can’t rule out the possibility of alien origins.

Inhospitable Earth

There’s also the fact that DNA and RNA – the building blocks of life as we currently know it – are rather unlikely candidates for survival on Earth, at least at the time when life on Earth began. Water is highly corrosive to both DNA and RNA, and yet Earth was covered entirely in the stuff in its early habitable days.

Yes, science is already pretty confident that life on Earth began in Earth’s oceans. But why would DNA and RNA become the basis for every genome on a planet covered in a substance that dissolves them? The possibility seems counter to any theory of natural selection.

Life is complex and fragile, yet it became incredibly tenacious on a just barely hospitable planet in a couple hundred million years. While not anywhere near conclusive, the miraculousness of it all is enough to consider at least the possibility that life had a head start elsewhere.

The Problem Of Proof

As with any theory on the origins of life on Earth, proving it is next to impossible because there were no eyewitnesses to the event. Scientists must rely on physical evidence that they’ve found on Earth and other planets to determine what happened.

If life on Earth did originate on another planet, what kind of proof would we expect to find, and where would we hope to find it? Current and future expeditions may uncover evidence of DNA- and RNA-based life on other planets, such as Mars. 

Given the complexity of DNA and RNA, the likelihood of evolving independently on two relatively nearby planets is incredibly low without some form of Panspermia. Finding similar life forms on two separate planets would be strong evidence that those life forms have the same planetary origin.

Contaminated Space

But even finding life on Mars wouldn’t be the end of the conversation. Humans on Earth have been sending machines into space for over half a century now. So if microbes can survive the journey from Mars to Earth inside a frozen rock, they can certainly survive a trip in the opposite direction, well protected inside a space-faring machine.

In which case, we may have artificially seeded other planets with life unintentionally. Whether that life actually survives and takes hold is a question of habitability and luck. But any signs of life found on Mars could be there due to unintentional contamination from Earth.

Needle In A Haystack

On the other hand, even if we never find signs of life on Mars, that wouldn’t necessarily disprove the Panspermia theory. Mars is a large planet that we still know relatively little about. Its landscape is still largely foreign, and potential life or signs of it could be hiding anywhere.

Short of scouring every inch of the planet’s surface, it would be impossible to conclusively say that there are no signs of life on Mars – only that none have been found that scientists can identify. 

Final Thoughts

There’s no reason life on Earth had to originate on Mars, either. It could have come from anywhere, within the solar system, or anywhere in the galaxy. It’s even possible that life from one planet seeded multiple other planets or that multiple planets seeded one.

With our currently available science, conclusively proving or disproving Panspermia is unlikely to happen any time soon. But the Panspermia theory, if true, has astounding implications. If life can be seeded from one planet to another, life may be much more common in the universe than we ever could have imagined. 

A History of Explanations of the Origin of Life

Spontaneous Generation

Panspermia

The Autotrophic Hypothesis

The Heterotrophic Hypothesis

Earth’s Primitive Atmosphere

The Stanley Miller Experiment

Coacervates Definition

The Endosymbiotic Hypothesis

The Origin of Photosynthesis and Aerobic Life