Recent comments in /f/askscience

Riptide360 t1_je5exgw wrote

Reply to How did eye lense evolve? by TheSonOfKayra

Your species relationship with food dictates a lot about how your eyes evolved.

In many land animals who eat primarily with their faces in their food they have an inner eye lid tied to the jaw muscle that closes during eating to keep food debris out. You can see the vestige of ours in the pink muscle stub in the inner corner of your eye and compare it to the full version found in your dog, cat or bird.

The placement of your eyes is also related to what you eat. Herbivore animals often have horizontal pupils, their day predator animals often have circular pupils and their night predator animals will frequently have vertical pupils. https://physicsworld.com/a/eye-shape-reveals-whether-animal-is-predator-or-prey/

In humans our ability to see in color was in part due to our evolution with gauging the effort to eat ripe fruit. This also improved our fore arms as more than legs and improved our hand eye coordination and thumb evolution.

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slouchingtoepiphany t1_je5evn4 wrote

Reply to How did eye lense evolve? by TheSonOfKayra

Here are a couple of links to articles that you might find interesting. Reference #1 posits that the evolutionary precusor to crystallins (a transparent protein that comprises the lens) occurred in sea squirts (Ciona). Reference #2 provides a review of how the crystallins evolved into two super families are kinds that we see today.

  1. https://pubmed.ncbi.nlm.nih.gov/16169492/
  2. https://pubmed.ncbi.nlm.nih.gov/23389822/
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Allfunandgaymes t1_je5cxbw wrote

Reply to Why are nonhuman erect bipedal animals so rare? by violetmammal4694

They're not. All birds are bipedal and are descended from bipedal dinosaurs that existed long before bipedal mammals. Those dinosaurs and their bird descendants - which are technically still dinosaurs by the way - are both classified as "theropods" due to their hip structure, which is what enabled them to become bipedal in the first place, as opposed to the "ornithischian", mostly quadropedal dinosaurs which are completely extinct.

In dinosaurs and birds, bipedalism evolved as adjustments to the hips and leg orientation. In humans, the spine also underwent significant changes to support a fully upright posture.

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mfb- t1_je5caed wrote

Reply to comment by phlpnow in Ask Anything Wednesday - Physics, Astronomy, Earth and Planetary Science by AutoModerator

> Clearly you don't have two angles to do this

For nearby stars you do. You measure their position in the sky, and then you measure again 6 months later when Earth is on the opposite side of the Sun. Twice the Sun/Earth distance is a short baseline compared to the distance to stars but angle measurements are precise. Stars move relative to the Sun so you need at least three measurements, and in practice you try to get even more to reduce uncertainties.

That method works up to ~10,000 light years or so (with a somewhat lower precision for distances beyond that). For stars farther away you use the cosmic distance ladder, which uses stars with well-known behavior nearby to determine the distance of equivalent stars farther away. Objects next to these can then be used to estimate the distance of even farther objects with the same method.

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mfb- t1_je5bjqa wrote

Reply to comment by Muhabba in Ask Anything Wednesday - Physics, Astronomy, Earth and Planetary Science by AutoModerator

That's the natural arrangement of a system with non-zero angular momentum where objects collide with each over time: A disk is the configuration you get after everything not in the disk collided with other particles. Planetary rings are pretty flat for the same reason: Here is a video explaining the concept.

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mfb- t1_je5b6p6 wrote

Reply to comment by tmoore82 in Ask Anything Wednesday - Physics, Astronomy, Earth and Planetary Science by AutoModerator

> Does an atom displace spacetime?

No.

> Is spacetime between the nucleus and the electrons?

There is space between them, i.e. they have some distance to each other (ignoring some technical details from quantum mechanics). That applies to all times, so you could say that there is "spacetime between them", but I don't think that's a useful way to view it. The same applies to all extended objects, including nuclei.

> Or is spacetime right beside me when I'm sitting in my living room?

Is "beside you" a place? Yes. That's part of space, which is a part of spacetime.

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MindlessCollar842 t1_je5as5e wrote

Reply to comment by dat_lpn_lifetho in Around 550 million years ago the earth's magnetic field almost collapsed, but then strengthened a few million years later. Scientists say this may have been due to the formation of the inner core. But why exactly would that cause the magnetic field to get stronger? by somethingX

It is not an easy subject to learn without foundation, and it looks like you may be confusing a few different subjects. We know quite a bit about the composition of the mantle. We can't drill to those depths, but it finds its way up (see: mantle xenoliths, ophiolites). Determining parentage and provenance of a magma body through chemistry is one of many applications of igneous petrology. If you would like references on mantle dynamics/geochemistry, please DM, I am happy to share.

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