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Whether we speak of the experience of living or the entirety of sentient beings on this planet, life has always been a concept that remains challenging for humans to fully comprehend. Even with life having existed on Earth for billion years, and humanity itself having walked this planet for countless millennia, there are still numerous unanswered questions about it. What is the purpose of life? Does life continue after death? These, along with many others, are classic inquiries in any philosophical discourse, questions as ancient as humankind itself.
Yet, there are also peculiar questions, unconventional doubts about life that rarely cross our minds during ordinary moments. Have you ever considered what Earth would be like if it lacked all forms of life? If so, this article is for you. If not, keep reading; some of the answers, or even the questions themselves, presented here will undoubtedly stir your thoughts.
10. How Much Life Has Ever Existed?
Today, the human population is nearing the eight billion mark. While this is a significant number, it pales in comparison to the 100 trillion ants that share the planet with us. Moreover, it’s estimated that, at any given moment, five nonillion bacteria are living on Earth—that’s a “5” followed by 30 zeros. It’s clear that there are countless life forms on our planet, and attempting to count them all would be an impossible task. And this is only referring to the life that currently exists. But what about all the life that has existed throughout history?
Determining the total number of creatures that could have inhabited Earth throughout the planet's history is an exceptionally challenging task. It is widely believed that complex life has existed on Earth for at least 570 million years. The fossils we’ve uncovered represent only a tiny fraction of the prehistoric remains that either remain hidden from us or have been obliterated by geological processes. Nevertheless, using their resourcefulness, scientists have established a connection between the number of fossils and known species to estimate the overall life that has ever existed. Experts today are largely confident that 99.9 percent of all species on Earth are extinct.
This figure makes sense when you consider that Earth's biosphere has experienced five mass extinctions over the past 400 million years. In each of these cataclysmic events, more than 80 percent of life forms were wiped out. A substantial portion of the scientific community believes that we are currently in the midst of a sixth mass extinction. Current estimates suggest species are disappearing 100 times faster now than before humans arrived, and in the past 50 years, humans have caused the loss of 60 percent of animal life. Sadly for us, death is far more common than life in this world.
9. Could Life on Earth Be Of Alien Origin?
At present, the majority of scientists are convinced that all life on Earth stems from a shared ancestor. This ancestral being was likely a simple unicellular organism, born from random chemical reactions on early Earth. However, the exact processes behind how life began remain a mystery, and all attempts to replicate the origin of life have been unsuccessful. Perhaps the answer to this puzzle lies within a theory called lithopanspermia.
The panspermia theory suggests that life on Earth may have been brought here from another location in the universe, such as nearby planets. Within this framework, lithopanspermia posits that rocky fragments from another planet, containing microbial life, were launched into space following a planetary collision. These space rocks eventually reached Earth millions of years later, and the life they carried began its evolutionary journey here. The idea behind panspermia was first proposed in France centuries ago and has been the subject of scientific inquiry ever since, although alternative theories have garnered more attention in recent times.
Despite the challenges, there are several signs that suggest lithopanspermia might have actually taken place. Through collision simulations, researchers at Pennsylvania State University have determined that it is statistically possible for a space rock containing microbes to travel between planets via ejection. Of course, there is the issue that space is far too inhospitable for life, with factors like radiation and extreme temperatures threatening survival. However, we are aware that several bacterial species can endure the harshest environments, from the hottest places on Earth to the vacuum of outer space.
Moreover, a recent study reveals that the fundamental elements that form life on Earth are widespread in stars, with these elements being more abundant towards the center of our galaxy than in our own solar system. To put it simply, the very matter we are composed of originates from a different part of the universe. Thus, life might not be as unique across the cosmos as we once thought.
8. Is It Possible to Be Both Dead and Alive Simultaneously?
The answer to this question doesn’t rely on any quantum theories where someone could exist in two states at once, nor does it refer to the concept of zombies, the classic depiction of the “living dead.” We can indeed say that certain organisms appear to be both alive and dead at the same time. But this largely hinges on the ongoing debate among scientists about what exactly separates a living being from inanimate matter.
Some scientists have proposed that all life forms must share fundamental traits in both their nature and behavior. As a result, in 1997, they created a list of seven criteria that something must fulfill to be classified as living. Every living organism must have a complex chemical composition and consist of basic structures called cells. It must have the ability to grow, reproduce, and respond to external stimuli. Additionally, the organism must possess a metabolism to generate energy and be capable of adapting to its environment.
Let’s now consider the case of viruses. Generally speaking, and even from a scientific perspective, viruses are regarded as biological entities—that is, they are living organisms. A virus contains complex genetic material and certainly adapts to its environment. However, a virus cannot grow or generate its own energy (it relies on the energy produced by its host). It also doesn’t reproduce; instead, it replicates itself by hijacking the host's cells. In fact, a virus is not made of a single cell, and it remains uncertain whether it immediately responds to external stimuli. While we know that a virus is alive, it does not fulfill most of the conditions necessary to be considered truly alive, resembling more of a machine than a living organism.
Interestingly, many non-living objects also meet several of these conditions, too. Even fire could have once been a difficult phenomenon to distinguish from a true living being. As our understanding of the elemental processes of life expands, we will likely gain a clearer distinction between living and non-living entities.
7. What Is the Total Weight of All Life?
Compared to the rest of our solar system, anyone observing Earth from space can easily see that it is a planet teeming with life. Over 30 percent of Earth's continents are covered by green vegetation, and combined with the vast blue oceans, Earth resembles a living oasis in the midst of cosmic emptiness. But one might wonder: what is the actual physical weight that life exerts on our planet? For obvious reasons, estimating the total mass of life on Earth was very challenging until recently. However, studies conducted in 2018 have shown that, in fact, all living creatures together are tiny compared to the immense size of our planet.
In May 2018, American scientists published a report that included calculations of the mass of all carbon-based life on Earth. Since all known life forms are carbon-based, and carbon is a prevalent element within every living being, using it to estimate total biomass seemed appropriate. The results revealed that all life on Earth weighs at least 550 gigatons of carbon, which is equivalent to 550 billion tons. Given that the entire Earth weighs approximately 6.57 billion gigatons, this means that all living beings combined account for only about one ten-millionth of the planet’s total mass.
As we observe, living nature constitutes just a small fraction of everything that makes up our planet. In this estimate, plant life alone accounts for more than 80 percent of the total biomass. In contrast, humans make up only 0.01 percent of all life forms. This is quite surprising, considering that our cities and buildings cover at least three percent of the Earth’s land surface, which is a significant proportion compared to the influence of other species. This means that although our numbers are few, we excel at what we do, for better or worse.
6. Can The Universe Be Alive?
Several philosophical theories suggest that the universe itself might be a living entity. For example, hylozoism posits that all matter is alive, while panpsychism proposes that every object in the universe possesses some degree of consciousness. These theories were largely dismissed after the acceptance of new concepts like evolutionism. However, recent discoveries and theories have given renewed momentum to the idea of a sentient universe.
For instance, some experts have speculated that consciousness could be an inherent feature of all existing structures. British physicist Roger Penrose theorized that human consciousness arises from quantum processes within small areas of our brain cells. Building on this, astrophysicist Bernard Haisch proposed that “quantum fields”—the fundamental structures that constitute the universe—might be capable of generating consciousness. In other words, any structure in the universe, whether a person or a star, could possess sentience, as quantum properties are part of its fundamental makeup.
On the other hand, both the structure and behavior of the universe provide possible evidence that the cosmos might indeed be a thinking entity. A 2005 study found that the complex structure of the material universe closely resembles the neural network of our brains. Moreover, it has long been recognized that the structure of an atom mirrors, in proportional distances, the planetary arrangement of our solar system. To top it off, new studies suggest that certain stars are making unexpected adjustments in their orbits across the galaxy. More research is needed to confirm whether this behavior is typical throughout the universe, but the concept of a living cosmos is captivating scientists more than ever.
5. Is Death the Same as Ceasing to Live?
The simple answer is no, it isn’t the same. Here’s the longer explanation: Our understanding of death has evolved over time, becoming more precise as our knowledge and technology improve. For instance, in the 19th century, a person was considered dead if they stopped breathing. A century ago, death was determined when the heart stopped beating. Nowadays, we consider death to occur when the body undergoes irreversible cellular damage—meaning the vital functions can no longer be restored.
However, even after death and the beginning of decomposition, it doesn’t mean the person is fully gone. In fact, recent studies reveal that some processes within a corpse challenge our traditional notions of death. A group of American and European researchers discovered in 2017 that after certain animals die, many of their cells continue to fight for survival. Not only do they remain active for days, but some cells even show increased activity.
It seems that, in an attempt to repair themselves, the cells in a deceased body accelerate the process of converting DNA into instructions to create new proteins. Furthermore, stem cells can continue functioning not for hours or days, but even for weeks after the organism’s death. This makes sense when we consider that animals are made up of various populations of different cells. As a result, some cells are more resilient than others, even after the body has seemingly died. The researchers also found that this behavior is seen in all multicellular organisms, including humans. Therefore, it’s clear that the distinction between life and death is much more ambiguous than we had previously thought.
4. Why Is There So Much Diversity in Life?
So far, scientists have identified and researched nearly two million different species of life. Among them, humans are part of a small group of 5,000 known mammal species. In contrast, we have cataloged 360,000 plant species and about one million types of insects. However, our understanding of Earth’s biodiversity remains quite limited, and experts believe there could be as many as two billion life-forms on the planet. Given that, as previously noted, almost all life on Earth is extinct, one might wonder: why is there such a vast diversity of living beings?
Life has an inherent tendency to keep multiplying, no matter the circumstances—even if it means drastically altering its form. Since life first appeared on Earth, the planet has experienced numerous mass extinctions, hundreds of mini ice ages, and constant sea level changes (ranging over hundreds of meters). Yet here we are, and research shows that biodiversity is growing faster than ever before, at an exponential rate.
This is mainly because, after every cataclysmic event that wipes out much of life, the surviving species tend to adjust to the new conditions, leading to the creation of new species. A clear example of this is the rapid diversification of mammals following the Cretaceous extinction event 66 million years ago. It is also well-established that ecosystems require species to specialize and support one another for survival. For instance, the air we breathe and the food we consume exist thanks to the contributions of plants and insects. Even forests become more resilient to disasters when they consist of a variety of tree species. In short, try to destroy life, and it will only thrive more.
3. When Do We Begin to Die?
Aging occurs when the number of new cells in our bodies is insufficient to replace those that are dying. Eventually, when too many cells have died or become nonfunctional, and our organs cannot operate as they should, death follows. In essence, we don't age or die as long as our body can maintain a balance in cell vitality. To put it simply, death happens when aging becomes too overwhelming for us. But the real question is: when does aging begin?
Throughout history, several literary figures and influential thinkers have argued that we start dying the moment we are born. This notion, while thought-provoking (and certainly a memorable phrase), doesn’t entirely hold up from a scientific perspective. For a child to mature into an adult, countless billions, even trillions, of body cells must be created, multiplied, and replaced along the way. During this time, the person doesn’t show noticeable signs of aging but instead becomes stronger both physically and mentally.
In fact, research has shown that up until the age of 25, the body creates more new cells than it loses. However, after the age of 25, the rate of cell death surpasses the rate of regeneration, which leads to the onset of aging. Furthermore, studies indicate that around the age of 24, the brain begins to experience a decline in cognitive speed. Thus, aging—ultimately leading to death—begins in our mid-twenties.
2. What Would Earth Be Like Without Life?
While it’s true that life, in terms of quantity, is a small part of what constitutes our planet, measuring living organisms by mass or volume is different from evaluating the impact these life-forms have on Earth. So, what would happen if life didn’t exist on Earth? It’s clear that without life, our beautiful blue planet would no longer be either beautiful or blue.
The Earth’s atmosphere contains 21 percent oxygen, a vital element for life forms like us. However, oxygen is an unstable gas that readily combines with other elements. It is the presence of plant life on the surface that continuously replenishes the atmosphere with oxygen, acting as a filter for the gas. Without life on Earth, only trace amounts of oxygen would remain in the atmosphere, which would instead be dominated by carbon dioxide. This shift would cause the temperature on the planet’s surface to rise dramatically.
As temperatures rise, the polar ice caps would begin to melt, leading to a dramatic increase in sea levels, possibly by tens of meters. Without life, the land would undergo rapid erosion, and mountainous areas would suffer severe damage. After a long period of time, it is speculated that the Earth’s temperature could climb to at least 290 degrees Celsius (554 °F). At this point, the oceans would boil away, rendering the planet entirely uninhabitable. Over millions of years, a thick layer of clouds could envelop the Earth, exacerbating the greenhouse effect, which would make the planet resemble Venus. While this might sound implausible, scientists suggest that Venus—now a hellish planet—was once home to liquid water and temperate conditions.
1. Which Organisms Have the Shortest and Longest Life Spans?
As we’ve observed, the diversity of life on Earth means that the concept of a long life varies drastically between species. What might be considered a long life for one organism could be incredibly brief for another. To understand this better, let’s explore the life spans of some vastly different organisms.
Starting with bacteria, their life spans are challenging to measure in the conventional sense, as they don’t grow like other living organisms. However, we can estimate their life span based on their reproduction cycle, also known as the generation time. This term refers to the time it takes for a cell to divide. Assuming a stable bacterial population, a bacterium will live for at least one generation time. The shortest-lived bacterium, Clostridium perfringens, has a generation time of just 6.3 minutes. In the time it takes to read four points of this list, a Clostridium perfringens bacterium will have lived and died.
In the animal kingdom, the mayfly Dolania americana likely has one of the shortest life spans. If we consider only the adult stage of its life cycle, during which the insect is fully developed, D. americana lives, reproduces, and dies in 30 minutes or less. On the other hand, a clam discovered in Iceland in 2006 was found to have lived for an astonishing 507 years, and it could have lived even longer had it not been killed after being collected.
We cannot overlook the incredible resilience of plants, which are among the longest-living organisms on Earth. For example, the oldest known individual tree is a bristlecone pine from California, which has been standing tall for over 5,060 years. When ancient humans were just beginning to develop written language, this tree was still in its early stages of life. On the opposite end of the spectrum, there are ephemeral plants, which have remarkably short life spans. One such example is the genus Boerhavia, whose members can complete their entire life cycle in under four weeks.
