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Ravi Kopparapu's Personal Meeting Room - Shared screen with speaker view
Seth Redfield
47:54
You highlighted the short PETM event in the isotopic record. Are there connections between the abrupt excursions and the longer-term variations? How easy/difficult is it to understand the drivers of the longer-term features? I’ve wondered if there are astronomical explanations (e.g., cosmic ray flux variations from heliospheric variations), but these would have a much harder time explaining the abrupt excursions.
David Grinspoon
01:01:52
If you were trying to find a civilization *exactly* like ours, you could look on the Moon. Although some might argue pessimistically that we barely made it there?
Joshua Pepper
01:04:15
Would a geostationary satellite be dynamically stable over these timescales?
Neal Sofge
01:05:29
No, it would be perturbed by the moon and end up either in solar orbit or falling back to Earth.
Mark Elowitz
01:06:22
Just a fun thought experiment: Would there have been enough time on Mars during the planet's warmer and wet (i.e. habitable) period for a technological civilization to have developed, and now all evidence for its existence has been erased?
Robert Scherrer
01:06:40
How detectable will our (fossilized) bodies be in the future fossil record?
David Grinspoon
01:07:10
https://lageos.gsfc.nasa.gov/Design/Message_to_the_Future.html
Jill Tarter
01:07:38
However, the Lageos satellites will be stable for 10’s of millions of years
VISHAL MAHENDRA (RA1711019010086)
01:08:30
how
David Grinspoon
01:08:31
Or better yet - Venus - which may have had habitable oceans for *billions* of years…?
Mark Elowitz
01:09:08
Our man-made lunar artifacts should be well-preserved over geological time spans.
David Grinspoon
01:09:57
That’s what I call the “Sapiezoic” Eon. In this case the Anthopocene is not just an Epoch, but civilization becomes integrated into planetary cycles, beginning a new Eon.
George Profitiliotis
01:10:27
Fascinating research topic! Can this line of research continue somehow?
Mark Elowitz
01:10:48
Did both Venus and Mars have a global magnetic field during their early epochs, which later decayed?
Jason Wright
01:12:54
What is the citation for Stride (2001)?
Karan Molaverdikhani
01:13:13
@Mark: Mars had one but Venus we don’t know.
Graham Lau
01:13:59
Love it!
Mark Elowitz
01:14:23
Thanks Karan
BMSIS Admin
01:14:27
Jason, I think this is it:
BMSIS Admin
01:14:28
Stride, S. L. (2001). An instrument-based method to search for extraterrestrial interstellar robotic probes. JOURNAL-BRITISH INTERPLANETARY SOCIETY, 54(1/2), 2-13.
Lev Horodyskyj
01:16:13
if there was even surficial mining (not just deep mining), wouldn't you expect a "technoturbation" signal in the geologic record that is identifiable?
Chris Bennett
01:17:45
Interesting talk - thank you. One interesting point regarding the evolution of life is the development of ecospace or niches of specialization … when species with specific roles are wiped out, it leaves a void for other species to fill in... this is what happened with the dinosaurs dying out and mammals taking over to pave the way to us … so bearing this in mind could it be possible that once a civilization on a planet develops, that given other species can fill in these niches, then once you have a civilization, you always have it … or is the nuclear option considered too 'final'?
Vladimir Airapetian
01:18:11
What about boron and gallium based silicon semiconductors as the signature to look?
Chris Bennett
01:18:42
(actually this question was essentially just asked as I was writing the same thing!)
Neal Sofge
01:19:31
Vladimir: analogous to the iridium layers? Is there enough of it?
David Grinspoon
01:21:32
@Chris great minds think alike…
Vladimir Airapetian
01:22:02
Sure, we need a consistent set of signatures along with iridium anomaly signature.
BMSIS Admin
01:22:49
Adam: visitation is only a paradox if we think we have searches well enough to rule out visitation
David Grinspoon
01:23:01
@Adam “Where *were* they?”
David Grinspoon
01:23:59
Venus may be much more promising both because the oceanic phase lasted much longer (We think) and the surface is completely unexplored!
Michael Way
01:24:56
We do not know if Venus ever had a mag field or not.
Robert Scherrer
01:25:09
RE: visitation. There's a cute SF story in which a space-faring family lands on Earth, and the father forces the daughter to throw out her aquarium before they leave. The result is the Cambrian explosion.
Michael Way
01:25:33
We also don’t know how important magnetic fields are for atmospheric escape. It’s still an open question, contrary to ‘popular’ opinion.
David Grinspoon
01:26:12
We also don’t know if a mag field really matters that much for preservation of habitable conditions on an earthlike planet.
David Grinspoon
01:26:26
Oh whoops, Michael just said that!
VISHAL MAHENDRA (RA1711019010086)
01:26:50
Magnetic field really matters for habitable zone
VISHAL MAHENDRA (RA1711019010086)
01:27:22
It does a lot of work to make it habitable
David Grinspoon
01:27:58
The Maven results at Mars suggest that Mag field can possibly do the opposite to what had been assumed. It may help *erode* an atmosphere! The net effect on habitability is really not well constrained.
Michael Way
01:28:19
Exactly David!
Neal Sofge
01:29:15
Are Van Allen belts necessary for habitability? Or at least, for complex enough life for intelligence?
David Grinspoon
01:30:21
A potentially permanent artifact of semi-intelligent life: https://www.heb.com/product-detail/hostess-twinkies/1704822
David Grinspoon
01:34:14
Thanks for a great talk and discussion!
Ensheng Weng
01:34:22
Thanks!
Mark Elowitz
01:34:26
Thanks Gavin for a very interesting talk!
VISHAL MAHENDRA (RA1711019010086)
01:34:31
Thank you