Recent comments in /f/askscience

SewFine69420 t1_jb3yev6 wrote

Reply to comment by Anonymous_Otters in Does the age of the universe depends on where you are? by _bidooflr_

This time stuff has been gnawing on my brain for years, as a fiction writer. In my writing I have beings that were born in different parts of the galaxy, some born on things that weren’t even planets or near a star, so I have a hard time trying to put forth how old they are, except to say they are ancient or ageless or something vague like that. If I try to put a number of years on them I immediately think “okay well they aren’t from earth nor are they on earth, so what exactly is a year in this context”. I have yet to settle on a solution.

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ParatusLetum t1_jb3xrdx wrote

Reply to During the last ice age, how long would it have taken for the ice sheets to form? by CDNEmpire

I was briefly a Geology Major long ago so some info may not be up to date.

1a. A quick look at that last glacial maximum shows time frames on 10’s of thousands of years. So the ice would be accumulating for around ~10-15 thousand years then declining to where we see it today possibly.

1b. Sounds about right. The “warm season” is not sufficient to erase the previous winters snow fall. A lot of these cycles seem to work on positive feedback loops. More ice > more light reflected back to space > colder weather > more ice etc. the condition will accelerate its effects until another factor steps in like natural variation in the earths tilt and orbit, or volcanic activity etc. which may cause a warming cycle to begin causing the ice age to diminish. Technically I believe we are still in an Ice Age as we have ice caps where as in the distant past earth did not have such caps year round possibly.

1c. Less significant variations than you may see today across the globe seems to most plausible.

  1. Weirdly most glaciation happens on land and land is mostly in the Northern Hemispheres. The glaciation would of had effects globally. Lowered sea levels had caused England to have more landmass and possibly even connected Australia to New Zealand by a land bridge now submerged. They would of had a wildly different ecosystem than they have now would be my guess. But they may be the reason they have such unique animals today.

All very cool questions. Keep on digging.

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djublonskopf t1_jb3x5ws wrote

Reply to What's the original function of recurrent laryngeal nerve? by CrazyisNSFW

In fish, the homologous nerve innervates the gills.

The difference is that in fish, the aorta doesn't come out of the heart. The heart pumps blood to the gills, and from the gills the oxygenated blood flows into the fish-aorta, which runs alongside the spine and carries blood to the rest of the body. Any nerve running in a straight line from the brain to the gills would pass between several major gill blood vessels to get there.

So once our ancestors developed lungs, we didn't need the blood from our hearts to run all the way up to where our gills used to be before reaching the aorta. Instead, one of the blood vessels that used to service the gills gets repurposed into our "aortic arch", and stays down close to the heart so it can connect up with the rest of the aorta down there.

So the nerve that in fish (and tetrapod embryos) runs directly from the brain to the gills (or what we've repurposed gill tissue into, various structures around our ears and throats) ends up between the heart and the aortic arch. So since the aortic arch stays down in the torso, and our necks develop in between our skulls and our torsos, the recurrent laryngeal nerve ends up stretched all the way down to where the aortic arch ends up, and then comes all the way back to where the "gills" are.

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i_love_rettardit t1_jb3vxkt wrote

Reply to If cancer is caused by mutations in genes that regulate normal cell development/division, how does killing cancer cells prevent it from coming back? by [deleted]

There are some heritable cancers e.g. retinoblastoma, look up Al Knudson's two-hit hypothesis. Or the BRCA genes. In those cases, where all cells have the mutation, yes indeed cancer is hard to defeat. This is why Angelina Jolie had her breasts removed and replaced, she carried the BRCA allele.

In more common cancer types, cancer is the result of cumulative mutations over a lifetime. Sequences of mutations occurring one after the other, over years, until it reaches the cancer breaking point. So to cure these patients means removing those cells with those mutations, a subset of all cells. To not cure, means some cells remained. Cells can be destroyed with surgery (removal), radiation, chemotherapy, immunotherapy (which stimulates the immune system to destroy them, elegant)

Now, there is also the concept of field cancerization, if a tumor is removed, neighboring cells have SOME of the mutations seen in the cancer, just not enough to be themselves cancer, having to do with this lifelong process of sequential cancer mutations. This is a serious topic among cancer surgeons - how much should I remove? Should I remove extra for fear of field cancerization?

Keep in mind, the standard line is that all cells in our body have the exact same genome, in truth that is not the case (as cancer shows us) and recent articles in top journals in the past year have implicated that even our non-cancer cells carry slightly different genetic variation, thought to be mutations in the first month or two in utero. This was done by correlating mutations found only in specific tissue types with the embryonic origin of those tissues. As such we can say our cells our all 99.99999% the same DNA sequence as each other, but there are small differences and major subpopulations.

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alt-mswzebo t1_jb3syzf wrote

Reply to Where does nitrogen in urine come from? by Easy-Care-7463

Answers here are focused on proteins and that is correct, but nucleotides (DNA and more abundant RNA) are also an important source of nitrogen in urine. In bacteria, there is about half as much nucleic acid by dry weight as protein. Nucleotides are less nitrogen-dense than proteins but still a major contributor to nitrogen in urine.

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