The sun is the center of our solar system and the source of nearly all energy on Earth. It provides warmth and light that sustain life and drive Earth’s weather, ocean currents, and climate. So what would happen if the sun suddenly disappeared? Could life on Earth survive without it? Let’s take a look at some quick facts to understand our reliance on the sun:
- The sun is a star at the center of our solar system. It is approximately 4.6 billion years old.
- The sun provides 99.86% of the total energy for the Earth’s climate system.
- Sunlight powers photosynthesis in plants and other organisms, providing the foundation of most food chains.
- The total solar energy absorbed by Earth is approximately 3,850,000 exajoules per year.
- Without the sun, the average temperature of Earth’s surface would be approximately -18°C (-1°F), far below the freezing point of water.
Clearly, the complete loss of the sun would have devastating consequences for life as we know it. But could any life possibly endure on a sunless Earth? Let’s investigate further.
The Immediate Aftermath
If the sun instantly disappeared, the first effect on Earth would be darkness. With no sunlight, vision-based organisms like humans and other species would lose their primary sense for navigating the world. Photosynthesis would also halt immediately, cutting off the energy source that the majority of life depends on.
Temperatures would start to drop almost instantaneously. Earth receives 1,366 watts of solar power per square meter at the upper edge of the atmosphere. Without this constant heat supply, temperatures would plummet from an average of about 15°C to -18°C in a matter of weeks.
The pace of cooling would vary across the planet based on local conditions. Areas with large bodies of water like oceans would retain heat longer thanks to the high heat capacity of water. In contrast, inland areas and places with dry air like deserts would cool exceptionally fast.
But the situation would become dire across all landscapes. Most plant and animal species alive today could not survive such a steep temperature drop. And frigid temperatures would be the least of their worries.
Oceans Frozen Solid
The freezing of the oceans would be one of the most devastating effects if the sun disappeared. With average temperatures rapidly declining to -18°C, the freezing point of seawater, the entire surface of the oceans would likely freeze solid within a year.
The freezing process would not be uniform, however. Based on simulations, some areas near the equator might initially be cold but not frozen, sustained by heat still remaining in the deeper ocean. But eventually, the whole ocean surface would freeze to depths of over 1 meter thick.
This would prove deadly for most marine life. Photosynthetic species like algae and phytoplankton would be the first to die out without sunlight. This would disrupt the base of the marine food web. Larger animals would soon suffer from lack of food sources and freezing temperatures. Even species adapted to polar climates would struggle with the sudden freezing of the global ocean.
The freezing oceans would also start to lock up one of the most important reservoirs of heat and water on the planet. This would speed up cooling of the atmosphere and end the water cycle as we know it. Next, let’s look at the drastic impacts on the atmosphere.
Changes in the Atmosphere
The atmosphere would undergo extreme changes if the sun disappeared. Here are some of the most significant:
- Cooling Troposphere – The troposphere, extending from the surface to 7-20 km up, would cool rapidly without solar heating. Average temperatures would plummet to around -18°C near the surface within weeks.
- Collapsing Stratosphere – The stratosphere, extending from the troposphere up to 50 km, would cool and collapse down toward the troposphere. The ozone layer within it would vanish.
- Condensing Water Vapor – With plunging temperatures, much of the atmosphere’s water vapor would condense and freeze out, drying the air.
- Stalling Weather Systems – Cooling air and collapsing stratosphere would disrupt atmospheric circulation, bringing wind and weather patterns to a halt.
- End of Hydrologic Cycle – The freezing oceans and condensing water vapor would shut down evaporation and precipitation, ending the global water cycle as we know it.
These atmospheric effects, especially the collapse of the stratosphere, would allow more cosmic radiation to reach Earth’s surface, causing additional harm to surviving species. Next we will consider extinction risks for different forms of life.
Risk of Extinction
Without the sun, most species on Earth would go extinct. Here we assess the risk of extinction for various life forms:
| Life Form | Risk of Extinction |
|---|---|
| Plants | Extremely high – Require sunlight for photosynthesis |
| Phytoplankton | Extremely high – Require sunlight for photosynthesis |
| Herbivores | Extremely high – Dependent on plants for food |
| Carnivores | Extremely high – Dependent on herbivores for food |
| Omnivores | Extremely high – Require plant or animal matter |
| Insects | Extremely high – Require warmth and plant matter |
| Fish | Extremely high – Most habitats would freeze over |
| Amphibians | Extremely high – Require warmth and humidity |
| Reptiles | Extremely high – Require warmth and sunlight |
| Birds | Extremely high – Require warmth, insects for food |
| Mammals | Extremely high – Require warmth and abundant food sources |
This illustrates that the vast majority of familiar life on Earth relies in some way on the sun and would likely perish without it. But some microscopic forms of life could possibly endure, as we will discuss next.
Extremophiles: Survival of Microbial Life?
While most complex life would not survive without the sun, some unicellular extremophiles might stand a chance. Extremophiles are microorganisms like bacteria and archaea adapted to live in very harsh conditions. Types of extremophiles include:
- Thermophiles – Thrive in extremely hot temperatures like hot springs
- Psychrophiles – Thrive in freezing cold like polar ice
- Halophiles – Require high salt concentrations
- Acidophiles – Thrive in highly acidic environments
- Alkaliphiles – Require highly alkaline conditions
- Radioresistants – Highly radiation resistant
Some of these extremophiles do not depend on the sun and obtain energy through chemical means like methanogenesis. They live in environments without sunlight such as volcanic vents, ocean sediments, and underground caves.
These microbial extremophiles represent Earth’s hardiest lifeforms. If any life could cling to survival on a frozen dark Earth, it would likely be simple subterranean and underwater communities of these highly resilient microbes. They would depend on geothermal heat and chemical sources of energy. Higher life forms would not be so fortunate.
The Fate of Humans
Humans and other complex organisms would fare extremely poorly if the sun vanished. Here are some key threats humans would face:
- Freezing temperatures – Average temperatures of -18°C would cause deadly hypothermia
- Darkness – Loss of vision and vital vitamin D production from sunlight
- Collapsing food chains – Disruption of agriculture and ecosystems for food
- Loss of fresh water – Disappearing liquid water due to freezing
- Unbreathable air – Condensing atmospheric water vapor reduces oxygen
- Cosmic radiation – Increased exposure without the sun’s magnetic field
Billions would likely perish in the initial waves of extreme cold, starvation, dehydration and radiation exposure. However, a small number of humans might survive by utilizing geothermal energy, growing mushrooms without sunlight, hunting subterranean fauna, and living under thick shielding. But these survivors would merely be delaying the inevitable. Without plants to provide food and oxygen, humans would eventually die out.
Earth’s Future Without the Sun
If the sun were to disappear entirely, Earth would be locked into a permanent ice age going forward. Here are some of the key characteristics of Earth’s long-term forecast without the sun:
- Average global temperatures of -18°C
- An icy global ocean frozen over 1 km deep
- A cold, dense atmosphere low in water vapor and oxygen
- Little to no precipitation or flowing water
- No weather patterns or ocean currents
- Pitch black skies with minimal heat retention
- A barren frozen landscape inhospitable to most life
Over millions of years, Earth would become geologically inactive and could possibly lose its atmosphere without the sun’s heating. The planet would bear closer resemblance to a cold, dry world like Mars than the lively blue marble we know today. Only the most tenacious extremophile microbes adapted to deep cold and darkness would endure.
Can the Earth Survive Without the Sun? Conclusion
In conclusion, while a small portion of microbial life could potentially cling to survival, most complex life including all plants and animals would certainly perish if the sun disappeared entirely. The complete loss of sunlight would lead to an irreversible cascade of freezing temperatures, frozen oceans, changes in the atmosphere and exposure to cosmic radiation that would extinguish the overwhelming majority of life in a relatively short time. Humans and other species would be faced with threats like hypothermia, starvation, dehydration and radiation poisoning. Earth itself would be locked into a frozen state inhospitable for most known forms of life, and could even eventually lose its atmosphere without the sun’s heating. Therefore, it is clear that the diverse ecosystems and life forms that thrive on Earth today ultimately owe their existence to the sun and could not survive without it in the long term. While microbial extremophiles might endure for some time underground, the sun is the only energy source capable of broadly sustaining complex life on Earth. Our planet would become a cold, barren world without the vital heat and light emanating from our nearby star.