I’m under the impression that most of the internal heat of the earth is due to radioactive decay. I was wondering if this source will run out before the sun’s light output changes significantly enough to wipe out most of life on earth. If this internal heat source diminishes enough to stop plate tectonics, wouldn’t the earth’s surface become increasingly flat? What would life be like? I guess most of the earth would be underwater. Would the pear like shape of our current earth remain so that we’d still have land? What’s the weather like?
I’m of the theory that giant octopi rule the ocean and their cousins rule the land. Mouse sized polar bears rule the north pole and giant penguins rule the the south pole.
I am not a geophysicist, but I believe the answer to your question is a qualified “we have no idea”. You have to remember, the subfield of plate tectonics is young–less than fifty years old–and the notion of radioactivity driving geophysical behavior is only slightly older. We also have a very limited ability to observe what is going on below the lower crust; almost everything we know about what goes on within the mantle and below is essentially inference from the residue of volcanic eruptions. We literally know more about what is going on below the photosphere of the Sun than we do about what happened beneath Earth’s crust. Scientists have recently estimated that the amount of energy released by radioactivity within the Earth is between 30 and 44 TW, but how steady that is and how long it will last (and indeed, the composition of isotopes and how they break down) is very much an area of active research. Here is a small sampling of articles on the topic:
Whenever the Earth’s core radioactivity runs out–should we call it “Peak Isotope”?–we’re going to have some eventual problems; without plate tectonics subduction and convection would stop, which would prevent renewal of landmasses or generation of new island archipelago. Existing small islands would disappear due to wind and wave erosion, and mountains would eventually diminish to an angle of repose of its consitutant materials. The overall effect on oceans, and therefore on the global climate, is uncertain, but the heat and movement generated by underwater subduction zones and geothermal vents would disappear, altering or destroying ecosystems in those areas.
Also, the Earth’s protective magnetic field–which slows or deflects the charged particles that comprise the incoming solar wind–would be diminished or likely disappear entirely, which may have dramatic effects upon life on Earth, exposing it to significantly more destructive and mutagenic radiation as more of the high energy particles enter the atmosphere, interact with air and generate hazardous lower energy ionizing radiation. UVA is going to be be the least of your problems.
Don’t worry, though; a “planet-killer” asteroid is likely to hit the planet long before that happens, and from what I hear there’s some discussion about demolishing the Earth to make way for a hyperspace bypass. I’d advise you to grab your towel and flag down the nearest passing flying saucer as soon as possible.
The currently accepted theory for the generation of Earth’s magnetic field is Dynamo theory, which involves the circulation of the Earth’s liquid iron core, which behaves essentially as a very viscous plasma. Without heating by radioactive decay which powers convection, the currents would slow or even stop, and there would be no MHD induction of a magnetic field. Planets and other celestial bodies without geological activity (Mars, the Moon) have little or no magnetic fields, while bodies with visible geological activity and presumably ferromagnetic cores (Earth, Io) tend to have detectable magnetospheres.
I want to note again that this is all current speculation; our understanding of what actually occurs is limited to inference, sympathetic mathematical modeling, and limited experiments on a small scale. This is by no means a mature, experimentially confirmed area of research, and our understanding of it could change dramatically with new data.
Thanks Stranger, I figured I could count on you for a well reasoned answer. I know the meaning of “Angle of Repose” from the Wallace Stegner novel. Wouldn’t every “mountain” eventually become an island due to the rising of the ocean level due to the filling in of the ocean’s depths by sediment? Each of the islands (originally the tallest mountains on the continents) would be subject to wave erosion, right? Also, wouldn’t wind erosion eventually (albeit at a much slower rate) reduce even the tallest mountains to sand dunes?
I was under the impression that there has never been an asteroid collision that has come close to destroying all life on earth. Now that the solar system is in it’s middle ages (I read that it’s got another 5 billion years before the sun goes red giant), is it likely that we will actually get hit by a planet killing asteroid or merely one that destroys 99% of life forms? I’m banking on the funding for the hyperspace bypass to not come through.
I’ve read this, too; I don’t know how much this would apply to Earth, though. Is the rate high enough to deplete the atmosphere? Mars is further away but much smaller (with a correspondingly lower escape speed), and we don’t know what the composition of a previous atmosphere might have been.
Erosion would continue but I doubt–within the stated time range, circa 4000 million years–that the contients would completely erode, or that there would be enough fillage from erosion to raise water levels to cover or nearly cover all landmasses. IANA geologist or geophysicst, though, so I could be–if you’ll pardon the expression–all wet in regards to that.
Nah, I was being facetious about the asteroid, but a large one striking the Earth certainly could mess up your whole lifestyle, and while it doesn’t happen very often, it still can occur; there are objects floating around the system in highly eccentric orbits that could smack into the Earth like a pitcher’s fastball hitting an unfortunate bird. As for the bypass, it’s got to be built and it’s going to be built, and you’ve had plenty of time to register a protest before now. I’ve got no sympathy…bloody pathetic planet…energize the cannon…
Venus is about the same size as the Earth and closer to the Sun and I believe it has essentially no magnetic field. Yet it has an atmosphere about 100 times as dense as Earth. So without an magnetic field, the Earth should have no problem holding on to its atmosphere.
As far as the OP goes, the Sun is slowly heating up as it ages. This is imperceptible to our instruments over the short time we’ve observed the sun. We know it because we’ve observed many other stars and deduced how stars age. Based on this, we expect the Sun to heat up so much that sometime in the next .5 to 1 billion years, it will be so hot that it will roast all the life on Earth. That is unless someone moves the Earth into a somewhat wider orbit so that it’s back in the habitable zone again.