Travel the universe with Dr. Ethan Siegel as he answers the biggest questions of all
Even if we don’t destroy ourselves, we always have the Universe to contend with.
Wiping out all life on Earth is hard, but causing mass extinctions is easy.
The 1991 eruption of Mt. Pinatubo was the largest volcanic eruption to occur in our lifetimes. One that was perhaps 10,000 times the magnitude of this could threaten human life on Earth, and perhaps volcanism was the cause of at least one of our previous major mass extinctions. (ALBERT GARCIA)
Five major extinction events have occurred since the Cambrian explosion, each eradicating over 60% of terrestrial species.
A measure of biodiversity, and changes in the number of genera that exist at any given time, to identify the most major extinction events in the past 500 million years. They are not periodic, and only the most recent one (from 65 million years ago) has a known cause. (WIKIMEDIA COMMONS USER ALBERT MESTRE, WITH DATA FROM ROHDE, R.A., AND MULLER, R.A.)
At least five extraterrestrial scenarios are capable of wiping humanity out.
A large, rapidly moving mass that strikes the Earth would be certainly capable of causing a mass extinction event. However, such events appear to be relatively rare. Even though asteroid and comet strikes are frequent, one that causes a mass extinction may be rare enough that no such strikes will occur for billions of years. (DON DAVIS (WORK COMMISSIONED BY NASA))
1.) Asteroid/comet strike: a giant impact triggered the last great mass extinction 65 million years ago.
The comet that gives rise to the Perseid meteor shower, Comet Swift-Tuttle, was photographed during its last pass into the inner Solar System in 1992. The influence of the gravity of the other planets has the potential to dramatically change its orbit, however, making it a potential threat to Earth in the year 4479. It has been called the single most dangerous object known to humanity by NASA. (NASA)
This illustration of the most distant gamma-ray burst ever detected, GRB 090423, is thought to be typical of most fast gamma-ray bursts. When one or two objects violently form a black hole, such as from a neutron star merger, a brief burst of gamma rays followed by an infrared afterglow (when we’re lucky) allows us to learn more about these events. The gamma rays from this event lasted just 10 seconds, but Nial Tanvir and his team found an infrared afterglow using the UKIRT telescope just 20 minutes after the burst. (ESO/A. ROQUETTE)
2.) Gamma-ray burst: the brightest electromagnetic events of all are a once-per-million-years risk.
What we perceive as a gamma ray burst is now known to have at least one identified cause: in merging neutron stars. If one of the jets from these mergers is pointed at Earth, and is close enough (within about 6,000 light-years), it could destroy the ozone layer, which would lead to humanity’s demise. (NASA / JPL)
If one occurred within 6,000 light-years of Earth, it would destroy our ozone layer, causing a mass extinction.
70,000 years ago, a brown dwarf pair known as Scholz’s Star, right on the precipice of igniting hydrogen fusion in its core, passed through the Solar System’s Oort cloud. Stars, failed stars, and stellar remnants pass through our Solar System multiple times every million years. (JOSÉ A. PEÑAS/SINC)
3.) A random encounter: the galaxy is full of stars, planets, stellar remnants, and black holes.
Over our Solar System’s 4.5 billion year history, the odds that a star would come as close to any of the planets as our Sun is to Pluto is approximately 1-in-10,000; the odds that a star would come as close to a planet as the Sun is to Earth (which would severely disrupt our orbit and cause Earth’s gravitational ejection) is less than 1-in-1,000,000,000. But if it happened, Earth would freeze over in short order, and human life would go extinct. (KEVIN GILL / FLICKR)
If one passes through our inner Solar System, it could gravitationally eject the Earth, destroying us all.
An optical composite/mosaic of the Crab Nebula as taken with the Hubble Space Telescope. The different colors correspond to different elements, and reveal the presence of hydrogen, oxygen, silicon and more, all segregated by mass. If the Earth were located within this nebula, which extends about 10 light-years across at present, it could cause an extinction-level event for humanity. (NASA, ESA, J. HESTER AND A. LOLL (ARIZONA STATE UNIVERSITY))
4.) A supernova: these have affected Earth many times, but we have endured without significant harm.
The supernova remnant Cassiopeia A contains signatures of a wide variety of elements of the periodic table, and would have emitted tremendous amounts of radiation when it first exploded. Type II supernovae are the most common class of supernova, but one would have to occur just a few light-years from us to eliminate our ozone layer, which should be rare enough that the estimated frequency is less than once per few billion years. (NASA/CXC/SAO)
A Type II supernova must occur within <25 light-years of Earth to endanger us, an extremely uncommon occurrence.
The Sun has increased in size, brightness, and temperature according to the curves above, and those three quantities will continue to evolve as shown by their respective lines into the future. By the time another ~2 billion years pass, its luminosity will be large enough to boil Earth’s oceans, effectively ending life on our planet. (WIKIMEDIA COMMONS USER RJHALL, BASED ON RIBAS, IGNASI (2010))
5.) Our own Sun: it will eventually incinerate us.
Today on Earth, ocean water only boils, typically, when lava or some other superheated material enters it. But in the far future, the Sun’s energy will be enough to do it, and on a global scale. (JENNIFER WILLIAMS / FLICKR)
After 2 billion years, the Sun’s increasing energy output will boil the oceans, unambiguously terminating all life on Earth.
If all else fails, we can be certain that the evolution of the Sun will be the death of all life on Earth. Long before we reach the red giant stage, stellar evolution will cause the Sun’s luminosity to increase significantly enough to boil Earth’s oceans, which will surely eradicate humanity, if not all life on Earth. (OLIVERBEATSON OF WIKIMEDIA COMMONS / PUBLIC DOMAIN)
Mostly Mute Monday tells an astronomical or scientific story in images, visuals, and no more than 200 words. Talk less; smile more.
