Earth gradually becomes uninhabitable over the next 1–3 billion years, with complex life disappearing long before the planet is finally swallowed by the expanding Sun as a red giant around 7.6 billion years from now.[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)]
## Detailed outline of the video
## Setup and assumptions (0:00–2:44)
- Introduces Earth’s future “extinction event” driven primarily by the gradual brightening of the Sun rather than asteroids or supervolcanoes.[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)]
- States assumptions: no human intervention is considered, and predictions are inherently uncertain over billion‑year timescales but grounded in geology, planetary science, and biochemistry.[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)]
## Shifting continents and supercontinent (2:44–5:32)
- Guest segment (Astrum Earth / James Stewart) explains ongoing plate tectonics with no sign of stopping, referencing Dr. Christopher Scotese’s models.[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)]
- Around 100 million years: Africa collides with Europe and Arabia, closing the Mediterranean, Red Sea, and Persian Gulf; a huge “Mediterranean Mountain Range” forms, possibly higher than Everest; Australia joins Southeast Asia; North America and Eurasia move apart.[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)]
- Around 250 million years: continents merge into supercontinent Pangea Proxima; Atlantic and Indian oceans close; South America wraps around Africa and Antarctica, creating an inland sea; ocean circulation is disrupted, deep waters lose oxygen, causing a major extinction; interiors of the supercontinent become hot semi‑arid/desert (up to about 55 °C), with only polar margins tolerable for mammals.[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)]
![[2026-01-20 21_25_57-2026_Spring_GAME2325_syllabus_jmp_a.pdf - Adobe Acrobat (64-bit).png]]
![[2026-01-20 21_26_26-.png]]
## Climate regulation and the carbonate–silicate cycle (5:32–7:14)
- Explains Earth’s long‑term CO₂ thermostat: volcanic CO₂, formation of carbonic acid rain, chemical weathering of silicate rocks, transport of ions to oceans, incorporation into marine shells (calcium carbonate), burial and subduction, and return of CO₂ via volcanism.[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)]
- Emphasizes that this cycle stabilizes climate over millions of years—until changes in the Sun’s brightness overwhelm it about 500 million years from now.[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)]
## Evolution of the Sun’s brightness (7:14–8:42)
- Describes main‑sequence evolution: hydrogen fuses to helium, core gets denser and contracts, outer layers move inward, releasing gravitational energy as extra heat and light, increasing luminosity.[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)]
- Notes the Sun is currently getting a bit over 1% brighter every 100 million years; in 500 million years it will be roughly 5% brighter, speeding chemical weathering, drawing down CO₂, and promoting ocean evaporation.[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)]
## Decline and extinction of plants (8:42–12:41, with ad break)
- Explains plant “compensation point”: photosynthesis gains vs. respiration losses; plants die if CO₂ falls too low to maintain a surplus of sugar.[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)]
- Distinguishes C3 and C4 photosynthesis: most plants (trees, grasses, many crops) are C3 and require relatively high CO₂; C4 plants (about 5% of biomass) are more efficient and can survive on much lower CO₂ (~10 ppm).[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)]
- Cites modelling that within ~500 million years atmospheric CO₂ drops below ~150 ppm, below the threshold for most C3 plants; extinctions occur gradually as groups fail earlier.[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)]
![[2026-01-20 21_27_07-.png]]
- C4 plants may persist 800 million–1.2 billion years into the future but eventually also succumb to the increasingly bright Sun.[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)]
![[2026-01-20 21_27_21-.png]]
## Collapse of animal life (12:41–14:07)
- As plants disappear, oxygen production plummets; atmospheric O₂ falls to about 1% of present levels.[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)]
- Complex animals die out, primarily from starvation as plant‑based food webs collapse, with herbivores disappearing first and carnivores shortly after.[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)]
## Loss of oceans and tectonic shutdown (14:07–18:16)
- About 1 billion years from now: roughly 27% of Earth’s current ocean volume has already been subducted into the mantle; the brightened Sun drives strong ocean evaporation, loading the atmosphere with water vapour.[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)]
- A thick, moist greenhouse atmosphere forms; as water vapour builds up it triggers a runaway greenhouse effect reminiscent of Venus, with temperatures rising uncontrollably; oceans are lost between roughly 1 and 1.5 billion years from now.[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)]
![[2026-01-20 21_27_58-.png]]
- Residual water persists in deep mantle reservoirs (possibly several “ocean equivalents”), slowly degassing, but only forming temporary, small polar lakes that are nutrient‑poor and short‑lived.[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)]
- Earth turns into a dry desert planet: dune fields at the equator, salt flats marking old ocean basins, and a desiccated crust; loss of water halts subduction, plate tectonics cease, and the surface begins to accumulate impact craters and hotspot shield volcanoes; long‑term volcanism adds CO₂, making the atmosphere denser and hotter.[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)]
- The last ecological refuges are underground ice caves and high mountain regions where small amounts of water linger; extremophile, salt‑loving microbes may survive in these niches and in cooler upper‑atmosphere layers.[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)]
## Final loss of life and red‑giant phase (18:16–end)
- About 2.8 billion years from now the Sun is ~28% brighter, and even polar temperatures reach roughly 190 °C; the last microbes die, leaving Earth lifeless.[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)]
![[2026-01-20 21_28_10-.png]]
- Around 3 billion years from now, hypothetical alien observers would detect no biosignatures, only a dead, cratered world.[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)]
- Roughly 6–7.6 billion years: the Sun exhausts core hydrogen, its core contracts, hydrogen burning in a shell causes it to expand into a red giant; luminosity rises to more than a thousand times current levels.[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)]
- Mass loss from stellar winds reduces the Sun’s gravity, letting outer planets move outward; Earth’s orbit expands to about 1.5 AU, but tidal interactions ultimately drag it inward again; at a radius of ~1.19 AU (about 256 times current) the Sun engulfs Earth and other inner rocky planets.[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)]
- Observations of red‑giant systems indicate inner planets are commonly destroyed, supporting this engulfment scenario.[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)]
- After the red‑giant phase, the Sun sheds its outer layers, leaving a hot white dwarf that cools over trillions of years; the narrator ends on a philosophical note about humans potentially altering this future via technology or escaping to other worlds, and about humanity being “stardust” returning to the stars.[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)]
## Time table of major future events
Approximate times are relative to _today_; values are the order‑of‑magnitude scales described in the video.
| Time from now | Major event / change | Description |
| ----------------------------- | ------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| 100 million years | Continental rearrangement | Africa collides with Europe and Arabia, closing the Mediterranean, Red Sea, and Persian Gulf; huge “Mediterranean Mountain Range” forms; Australia joins SE Asia; North America and Eurasia further separate.[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)] |
| 250 million years | Pangea Proxima forms | Supercontinent Pangea Proxima assembles as Atlantic and Indian oceans close; South America wraps around Africa and Antarctica, forming an inland sea.[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)] |
| 250+ million years | Ocean circulation disruption | Supercontinent geometry disrupts thermohaline circulation; deep oceans lose oxygen, causing a major marine extinction; interiors of the supercontinent become hot semi‑arid/desert (up to ~55 °C).[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)] |
| 500 million years | Sun ~5% brighter, CO₂ crash begins | Sun’s luminosity ~5% higher than today; enhanced weathering draws down CO₂ faster than volcanism can replenish it, initiating long‑term CO₂ decline and “plant‑pocalypse.”[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)] |
| ~500 million years | C3 plants mostly gone | As CO₂ falls below ~150 ppm, most C3 plants (trees, many crops, grasses) can no longer photosynthesize effectively and progressively go extinct.[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)] |
| 800 million–1.2 billion years | C4 plants’ last stand | More efficient C4 plants, able to function at very low CO₂ (~10 ppm), persist into this window but eventually succumb to heat and environmental stress.[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)] |
| ~1 billion years | Sun ~10% brighter | Surface temperatures may reach ~50 °C globally; deserts expand, oceans evaporate faster than rainfall; complex ecosystems collapse.[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)] |
| ~1 billion years | Complex animals extinct | With plants gone and O₂ falling to ~1% of current levels, complex animals die out, primarily from starvation and secondarily from lack of breathable oxygen.[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)] |
| 1–1.5 billion years | Surface oceans lost | Roughly 27% of ocean water has been subducted into the mantle while the rest evaporates; a moist greenhouse transitions to runaway greenhouse, eliminating global surface oceans.[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)] |
| >1 billion years | Desiccated, tectonically dead Earth | Earth becomes a desert world with vast dune fields and salt flats; lack of water halts subduction and plate tectonics; shield volcanoes and impact craters dominate the surface; volcanism slowly enriches the atmosphere in CO₂.[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)] |
| 1–3 billion years | Microbial refuges then extinction | Only extremophile microbes persist in underground ice caves, mountain niches, or cooler upper atmosphere; by about 2.8–3 billion years from now even these last life forms die out.[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)] |
| ~3 billion years | Lifeless Earth | No detectable biosignatures remain; Earth appears as a barren, stagnant rocky planet to distant observers.[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)] |
| ~6 billion years | Sun leaves main sequence | Core hydrogen exhausted; fusion stops in the core, which collapses; hydrogen burning begins in a shell around the core, initiating subgiant/red‑giant evolution.[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)] |
| ~7–7.6 billion years | Sun’s red‑giant peak and Earth’s engulfment | Sun’s luminosity exceeds 1000× current value; radius grows to ~1.19 AU; despite initial orbital expansion to ~1.5 AU, tidal forces drag Earth inward and it is engulfed and destroyed.[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)] |
| >7.6 billion years | White dwarf Sun | Sun sheds outer layers, leaving a hot white dwarf that slowly cools over trillions of years, with no surviving inner planets.[[youtube](https://www.youtube.com/watch?v=bwzTr49rPw8)] |