Anyone with the basic understanding of cosmology is aware of the certainty that, sometime in the distant future, our Earth will die. But the question is how and when. The death of the Earth can be explained in two ways; biologically and geologically.
The Earth, according to radiometric dating, was created 4.5 billion years ago. From that point in time, it took one billion years or so for life to appear for the first time. Since then, it survived multiple periods of glaciations, asteroid impacts, and several mass-extinctions. In the last hundred years alone, the Earth experienced nuclear war as going through drastic climatic changes. So when will the Earth die? It’s a question that scientists have been trying to solve for a long time, and it doesn’t have a simple answer.
Based on our knowledge of the Earth, solar system, celestial mechanism, and other similar fields, researchers have been able to conclude scenarios that could lead to the destruction of the planet.
Human Influence on The Earth’s Future
The sixth and the ongoing mass extinction, known as Holocene extinction, is a direct result of human activities on the Earth. According to 2019, the Global Assessment Report on Biodiversity and Ecosystem Services, close to a million animal and plant species face extinction within a few decades due to increasing human influence.
Since the 1950s, the explosive population growth accompanied by technological advancements by humans has made a massive impact on Earth’s ecosystems. Many species of mammals, reptiles, fishes, and invertebrates that once populated the planet, are now extinct.
The current rate at which species are going extinct is estimated to be as much as a thousand times higher than average background extinction rates. The concentration of carbon dioxide in the atmosphere is up by 30 percent since the industrial revolution.
There are several ways human actions can contribute to their demises, such as a nuclear holocaust, a disaster caused by an experiment, or a genetically engineered disease.
A Nuclear Famine
A mushroom-shaped cloud, and water column resulting from an underwater explosion during the Operation Crossroads Baker on July 25, 1946.
Nuclear weapons, one of the most important discoveries of the 20th century, can have a disastrous effect on all life forms on Earth. Large-scale nuclear warfare on the planet’s surface would likely lead to hypothesized catastrophes like ‘nuclear winter.’
Theoretically, the fallout released after the detonation of nuclear weapons would block most of the direct sunlight reaching the Earth’s surface resulting in a global cooling leading to widespread crop failure and famine, often termed as ‘nuclear famine.’ According to a 1983 study conducted by a group of researchers, high levels of ultraviolet radiation, low temperature, and visibility for an extended period could dismantle the vital support systems of a civilization.
Nuclear warfare of significant size would likely have long-term effects, primarily from the fallout released, and could also lead to a “nuclear winter” that could last for decades, centuries, or even millennia after the initial event.
According to the 2013 International Physicians for the Prevention of Nuclear War report, more than two billion people would face starvation if a nuclear exchange were to occur between India and Pakistan.
Asteroid And Comet Threat
Artist’s concept of a collision between two astronomical bodies | Image Courtesy: NASA
Time Frame: 500 million years at least
A massive asteroid impact that occurred about 66 million years ago is considered by many as a crucial factor in the extinction of dinosaurs from the face of the Earth. It is plausible that a similar event could do the same to the human race. But when can we expect one?
While asteroid (as well as comet) impacts are not uncommon and have been witnessed throughout the solar system, major events are the ones that appear to have significant effects. If we take a brief look at the Earth history, such impacts are much involved in the evolutionary history of life from the formation of the Moon to the origin of water and several mass extinctions as well.
Extensive research on past asteroid impacts indicates an inverse relationship between the size of the objects and frequency of their collision with the Earth. Asteroids (objects) with a diameter of 1 km strike the planet every 500,000 years while collision with large objects with a diameter of 5 km happen once in 20 million years.
The last known impact of an asteroid with a diameter of more than 10 km occurred about 66 million years ago. The timing of the impact aligns perfectly with the Cretaceous–Paleogene boundary.
In 1979, geologists discovered a large impact crater in Western Australia. It was only recently that researchers were able to determine its age, which is now believed to be 2.2 billion years. Here again, the crater’s age concurs with the end of one of the major ice ages.
Predicting a significant asteroid or meteor impact is not easy. It could happen in the next 500 million years or a couple of billion years.
Gamma-Ray Burst or GRBs
Mechanism of Gamma-ray bursts | Image Courtesy: NASA
Time Frame: 500,000 years?
Gamma-ray bursts or GRBs are energetic electromagnetic outbursts that occur randomly throughout the universe. They are dangerous and harmful to all life forms. Fortunately, all recorded GRBs to date have occurred outside our galaxy.
A leading theory regarding the GRBs is that life is more likely to flourish in outer regions of a galaxy, where Gamma-Ray Bursts are rare.
Life on Earth is relatively safe from Gamma radiation not just because of Earth’s location in the Milky Way galaxy but its atmosphere as well since it absorbs most of the ionizing radiation (x-rays and gamma-rays) it receives. The most probable outcome of a Gamma-Ray Burst within, let’s say, 6000 light-years from the Earth is a slight increase in ultraviolet radiation for a few seconds.
However, if (even from the same distance) the path of the GRB emission crosses straight through the Earth, then it could be devastating and can trigger mass-extinction.
In August 2017, space observatories detected a short gamma-ray burst about 130 million light-years away at the Hydra constellation. The GRB (designated as designated GRB 170817A) was caused by the merger of two neutron stars. It’s the closest GRB observed to date.
Surprisingly, no GRBs have been observed in the Milky Way Galaxy, which remains a mystery. Researchers, however, have been able to identify a possible GRB candidate. A Wolf-Rayet Star (WR 104). located about 8,000 light-years away is likely to explode into a supernova in 500,000 years. When it does, a GRB will occur. There is only a small chance that our planet will be in the path of its powerful emission.
Increased Solar Radiation and Extinction of Complex Life Forms
Time Frame: 600 million to 1.3 billion years
The Sun, being the only star in our solar system, has a strong influence on all the planets, including the Earth. Its energy (sunlight) is essential for the survival of every single organism on Earth. But have you ever thought, what will happen to the Sun in the future? And what effects will it have on the planet(s)?
Over time, Sun’s luminosity will gradually increase, resulting in high levels of solar radiation reaching the Earth’s surface. The current rate of increase in Sun’s luminosity is around 1 percent in 100 million years and 10 percent in 1 billion years. It is estimated that in the last 4.5 billion years, the brightness has gone up by 30 percent.
As the level of solar radiation reaching the Earth’s atmosphere increases the weathering of silicate minerals occurs at higher rates. In the next 600 million years, the CO2 concentration is expected to drop below a point at which C3 carbon fixation photosynthesis cannot be sustained.
At this stage, a gradual decline in trees and forests life is likely to be seen. Herbaceous plants (C3) are among the first plants to disappear from the Earth, followed by deciduous forests and, at last, evergreen forests.
The decreasing carbon dioxide level in the atmosphere will trigger a chain of events that will eventually lead to the extinction of multicellular life forms.
Evaporation of World’s Oceans
Time Frame: 1.1 billion to 2.8 billion years
In about 1 billion years from now, when the solar luminosity is 10 percent higher than the current level, the average global temperature will be around 47 degrees Celsius or (116 degrees F). At this point, the planet will experience a runaway greenhouse effect resulting in ocean evaporation over the next 100 million years.
However, the total loss of the world’s oceans could be slowed down by a lower atmospheric pressure condition. If the atmospheric pressure were to decrease in the future, it would reduce the greenhouse effect, thus effectively lowering the global temperature.
With the increasing solar luminosity, the Earth’s surface temperature is likely to reach 149 degrees Celsius (or 300 degrees F) in 2.8 billion years. Under such conditions, the planet’s biosignatures are expected to vanish as well.
Beyond that point, the planet could experience a steady increase in temperature. However, it could also go through (if liquid water still exists) moist greenhouse effect. If that’s the case, the surface temperature of Earth could reach 1,300 degrees Celsius in 4 billion years.
The Earth Gets Swallowed By The Expanding Sun
The current size of the Sun compared to its estimated size during the red-giant phase | Image Courtesy: Wikimedia Commons/Mysid
Time frame: 6 billion to 7.6 billion years
The Sun was formed about 4.6 billion years ago, and according to the stellar evolution theory, it has already spent half of its life. The star has remained stable for most of its life. However, once the hydrogen runs out of its core, it will go through rapid and rather violent changes.
Every second, it is burning about 600 million tons of hydrogen into helium to generate energy. It takes about 10,000 to 170,000 years for this energy to escape from the core.
In about 5.4 billion years from now, the Sun will enter the red giant phase (it doesn’t have enough mass to explode into a supernova). For about one billion years after that, it will expand more than two hundred times than its current size and will swallow planets Mercury, Venus, and most likely the Earth.
There are stars within our galaxy, which are known to move independently. Since the Sun and the entire solar system revolves around the galactic core, there is a slight possibility that we encounter one such runaway star. The event, as expected, can disrupt the current picture of our solar system. Another star in the neighborhood is likely to attract a high number of asteroids in the inner solar system that could only be dangerous. Long term gravitational perturbations in orbits of the planets should also be taken into consideration.
According to the most recent studies, the moon is moving away from the Earth by 5 cm per year. And if, by any chance, both the planet and its satellite manages to survive being devoured by the expanding Sun, then it’s likely that they remain tidally locked but with a larger and more stable orbit. This process will transpire in about 50 billion years from now.
After the red giant phase, the Sun will transform into a white dwarf. As a white dwarf, which is about 200,000 times denser than the Earth, the Sun will exert far greater gravitational pull than it does now. The annihilation of remaining inner planet(s) as well as Jupiter and Saturn over time is likely at this point.
Even now, let’s say the Earth miraculously escapes from its total obliteration, what then? If that’s the case, the ultimate fate of the planet earth is to be devoured by black dwarf (theoretical end of the life cycle for Sun-like stars) Sun in trillions of years.