Score
Title
98
AskScience Panel of Scientists XVIII
550
AskScience AMA Series: I am Melinda Krahenbuhl and I am the director of the Reed Research Reactor, the only nuclear reactor operated primarily by undergraduate students. AMA!
8468
What elements are at genuine risk of running out and what are the implications of them running out?
269
Can you break sound barrier under water or any other material?
4021
What’s the largest star system in number of planets?
19
Why does plastic turn white at the creases when folded/bent?
3
How does thermal imaging work?
21
Do microwaves leave residual changes to molecules after heating?
4
Can a setup of hall engines provide enough thrust to keep a satellite stationary above earth?
2
Does the temperature have any (noticable) effect on air resistance?
6
How does a memristor work?
1
How does radiation poisoning work?
1
How is the height of the mountain measured?
3827
What is the effect, positive or negative, of receiving multiple immunizations at the same time; such as when the military goes through "shot lines" to receive all deployment related vaccines?
4
If a planet had a radius that was equal to the altitude of Earth’s geosynchronous orbit, but had the same mass and rotational period as the Earth now, would there be reduced or zero gravity on the surface?
1
What is lost and what is preserved in a particle collider?
8
Why does snow melt in the sunlight, even when the temperature outside is below freezing?
11
Mar's summer temperature can be 20 celsius. Could a human survive with just an oxygen mask?
2
Is there an altitude at which there is no longer a speed of sound?
0
How would a moving target affect the rate of nuclear fission vs a stationary target?
14
What would a spaceship moving at 0.9c firing lasers both in front of it and behind it look like to an external reference frame?
6
Does adiabatic warming occur when air descends in the Earth's polar cells?
24
How does the cosmic microwave background persist? Why hasn't it been distorted and destroyed by new sources of energy pumping into space?
6
How does cancer metastasis work?
7
Can a comet maintain an atmosphere?
1
How does RFID blocking material work?
0
Does the Meissner effect relate to Lenzs law?
9
Why hasn't The Asteroid Belt formed a planet?
10
Can you use a normal (CMOS) camera for detecting scintillation?
3
How do people know that the Island of Stability exists? And could there possibly be another "island" after it?
59
How can brain cells cause tumours even though they can not multiply?
7
How far back can you go before carbon dating becomes unreliable?
2
How does a computer process “simple” events?
1578
Ask Anything Wednesday - Biology, Chemistry, Neuroscience, Medicine, Psychology
3
What is the nonrenewable fuel cost to produce x quantity of electricity?
1132
What triggers beta particles to form, and for what reason can they not penetrate substantially thick aluminium?
0
What is the strongest a magnet could be?
1242
If capacitance increases as distance between plates decreases, why aren't there very small 1F capacitors?
0
What makes astronomers think life in general isn't possible on gas giants?
1
How applicable are Newtonian Physics in real life? Is it completely false or are there some concepts which can be used to accurately predict real-life situations?
1050
is it possible to move an object in circular motion using magnets?
4
What would hydrogen in metal form look like?
40 CrustalTrudger > Could a meteor have struck Earth so hard as dislodge soil or rocks, shoot them into the atmosphere Yes, at least on the rocks parts (any unconsolidated material like soil would not survive the process). A good analogue are [Martian meteorites](https://en.wikipedia.org/wiki/Martian_meteorite). These are meteorites that fell on Earth, but were originally part of the Martian crust that were ejected from Mars during meteorite impacts on Mars. > and spread life into space? Little more uncertain. As discussed above, there is certainly the expectation of a decent amount of material from Earth that has been distributed throughout the solar system via impacts. For example, calculations considering the Chicxulub impact (the one thought to have brought about the K-T extinction) suggest that a [volume of Earth material equal to the size of the impactor was ejected into space](https://arxiv.org/abs/1204.1719). More general calculations [predict massive amounts of material were transferred between planets via ejecta, but mostly during the late heavy bombardment period between 3.8 and 4.0 billion years ago](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3440031/). The real questions to which we don't know the answer are 1) how much of this ejecta was life bearing (i.e. we still have limited evidence of life on Earth from the before or during the late heavy bombardment, but some signs point to there being some microbial life at that time) and 2) under what circumstances (if any) would microbes ejected into space via this process remain viable? There are suggestions that depending on the size of the debris, [some viable DNA/RNA within microbes could survive for several million years](http://iopscience.iop.org/article/10.1088/0004-637X/690/1/210/pdf), but it's still uncertain whether that is actually quick enough for these ejecta to end up on a planet/moon where life could flourish (seems like a long time, but consider that many of the asteroids and meteors have been orbiting the sun without impacting large planets or moons since at least the end of the late heavy bombardment period 3.8 billion years ago).
7 LeonAnon The main problem with that is that the distance between stars is mindbogglingly large. The nearest next star is at 250000 AU, compared to 40 AU for Pluto. So by the time any microbes/life would have crossed the gap, their DNA (or equivalent) would have degraded beyond repair by hard cosmic radiation. Even on Earth, which is moderately shielded against radiation, DNA/RNA [completely degrades within 3-7M years](http://rspb.royalsocietypublishing.org/content/279/1748/4724), and gets fragmented beyond repair long before that. And then those fragments would still have to survive reentry on a new world.
6 64vintage I have read that since the origin of life on earth, there have been at least one and possibly multiple times when the surface of the earth was entirely uninhabitable - molten etc. Since the theory is that life evolved only once, the conclusion is that the earth was re-seeded by former ejecta that returned to earth many years later, when conditions were less hostile. On that basis, the answer to your question is yes. EDIT : https://nai.nasa.gov/annual-reports/2002/uw/giant-impacts-in-earths-early-history-reseeding-the-planet-and-the-search-for-earth-rocks-on-the-moon/ " Project Progress We explore the likelihood that early remains of Earth, Mars, and Venus have been preserved on the Moon in high enough concentrations to motivate a search mission. During the Late Heavy Bombardment, the inner planets experienced frequent large impacts. Material ejected by these impacts near the escape velocity would have had the potential to land and be preserved on the surface of the Moon. In order to determine whether the Moon has preserved enough ejecta to justify a search mission, we calculate the amount of Terran material incident on the Moon over its history by considering the distribution of ejecta launched from the Earth by large impacts. In addition, we make analogous estimates for Mars and Venus. We find, for a well mixed regolith, that the median surface abundance of Terran material is roughly 7 ppm, corresponding to a mass of approximately 20,000 kg of Terran material over a 10 × 10 square km area Mounting attention has focused on interplanetary transfer of microorganisms (panspermia), particularly in reference to exchange between Mars and Earth. In most cases, however, such exchange requires millions of years, over which time the transported microorganisms must remain viable. During a large impact on Earth, however, previous work (Armstrong et al., submitted) has shown that substantial amounts of material return to the planet of origin over a much shorter period of time (< 5000 years), considerably mitigating the challenges to the survival of a living organism. Conservatively evaluating experiments performed on Bacillus subtilis and Deinococcus radiodurans to constrain biological survival under impact conditions, we estimate that if the Earth were hit by a sterilizing impactor ~ 300 km in diameter, with a relative velocity of 30 km s-1 (such as may have occurred during the Late Heavy Bombardment), an initial cell population in the ejecta of order 10-4 – 10-2 cells kg-1 would in most cases be sufficient for a single organism to survive and return to an again-clement planet 3000-5000 years later. Although little can be said about the characteristics or distribution of ancient life, our calculations suggest that impact re-seeding is a possible means by which life, if present, could have survived the Late Heavy Bombardment."
42 0 CrustalTrudger > Could a meteor have struck Earth so hard as dislodge soil or rocks, shoot them into the atmosphere Yes, at least on the rocks parts (any unconsolidated material like soil would not survive the process). A good analogue are [Martian meteorites](https://en.wikipedia.org/wiki/Martian_meteorite). These are meteorites that fell on Earth, but were originally part of the Martian crust that were ejected from Mars during meteorite impacts on Mars. > and spread life into space? Little more uncertain. As discussed above, there is certainly the expectation of a decent amount of material from Earth that has been distributed throughout the solar system via impacts. For example, calculations considering the Chicxulub impact (the one thought to have brought about the K-T extinction) suggest that a [volume of Earth material equal to the size of the impactor was ejected into space](https://arxiv.org/abs/1204.1719). More general calculations [predict massive amounts of material were transferred between planets via ejecta, but mostly during the late heavy bombardment period between 3.8 and 4.0 billion years ago](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3440031/). The real questions to which we don't know the answer are 1) how much of this ejecta was life bearing (i.e. we still have limited evidence of life on Earth from the before or during the late heavy bombardment, but some signs point to there being some microbial life at that time) and 2) under what circumstances (if any) would microbes ejected into space via this process remain viable? There are suggestions that depending on the size of the debris, [some viable DNA/RNA within microbes could survive for several million years](http://iopscience.iop.org/article/10.1088/0004-637X/690/1/210/pdf), but it's still uncertain whether that is actually quick enough for these ejecta to end up on a planet/moon where life could flourish (seems like a long time, but consider that many of the asteroids and meteors have been orbiting the sun without impacting large planets or moons since at least the end of the late heavy bombardment period 3.8 billion years ago).
8 0 LeonAnon The main problem with that is that the distance between stars is mindbogglingly large. The nearest next star is at 250000 AU, compared to 40 AU for Pluto. So by the time any microbes/life would have crossed the gap, their DNA (or equivalent) would have degraded beyond repair by hard cosmic radiation. Even on Earth, which is moderately shielded against radiation, DNA/RNA [completely degrades within 3-7M years](http://rspb.royalsocietypublishing.org/content/279/1748/4724), and gets fragmented beyond repair long before that. And then those fragments would still have to survive reentry on a new world.
4 0 64vintage I have read that since the origin of life on earth, there have been at least one and possibly multiple times when the surface of the earth was entirely uninhabitable - molten etc. Since the theory is that life evolved only once, the conclusion is that the earth was re-seeded by former ejecta that returned to earth many years later, when conditions were less hostile. On that basis, the answer to your question is yes. EDIT : https://nai.nasa.gov/annual-reports/2002/uw/giant-impacts-in-earths-early-history-reseeding-the-planet-and-the-search-for-earth-rocks-on-the-moon/ " Project Progress We explore the likelihood that early remains of Earth, Mars, and Venus have been preserved on the Moon in high enough concentrations to motivate a search mission. During the Late Heavy Bombardment, the inner planets experienced frequent large impacts. Material ejected by these impacts near the escape velocity would have had the potential to land and be preserved on the surface of the Moon. In order to determine whether the Moon has preserved enough ejecta to justify a search mission, we calculate the amount of Terran material incident on the Moon over its history by considering the distribution of ejecta launched from the Earth by large impacts. In addition, we make analogous estimates for Mars and Venus. We find, for a well mixed regolith, that the median surface abundance of Terran material is roughly 7 ppm, corresponding to a mass of approximately 20,000 kg of Terran material over a 10 × 10 square km area Mounting attention has focused on interplanetary transfer of microorganisms (panspermia), particularly in reference to exchange between Mars and Earth. In most cases, however, such exchange requires millions of years, over which time the transported microorganisms must remain viable. During a large impact on Earth, however, previous work (Armstrong et al., submitted) has shown that substantial amounts of material return to the planet of origin over a much shorter period of time (< 5000 years), considerably mitigating the challenges to the survival of a living organism. Conservatively evaluating experiments performed on Bacillus subtilis and Deinococcus radiodurans to constrain biological survival under impact conditions, we estimate that if the Earth were hit by a sterilizing impactor ~ 300 km in diameter, with a relative velocity of 30 km s-1 (such as may have occurred during the Late Heavy Bombardment), an initial cell population in the ejecta of order 10-4 – 10-2 cells kg-1 would in most cases be sufficient for a single organism to survive and return to an again-clement planet 3000-5000 years later. Although little can be said about the characteristics or distribution of ancient life, our calculations suggest that impact re-seeding is a possible means by which life, if present, could have survived the Late Heavy Bombardment."