ELI5

01 Jun 2017 20:28

Yes, fire did burn differently because of excess oxygen fuel. During the carboniferous period, 300-350 million years ago, oxygen levels reached as high as 35%, compared to today's ~20%. This allowed fires to start in places which we wouldn't normally expect (places of high humidity, during rain storms). Today we find fossilized charcoal in coal beds that arose from peat bogs, which grants credence to the idea that fires did burn much more easily during this period. You might ask "how did plants survive the constant danger of fire?" Adaptation thanks to random evolution. For example, plants from this period expressed deeper roots/tubers than their modern day counterparts, and the leaves of trees were higher which could help avoid catching fire from a stray brush fire.
The reason so much coal (a large part of which is oftentimes fossilized charcoal) remains from this period is due to two factors, as other posters have mentioned. First The structural material of plants, lignin, doesn't burn rapidly, (paper is often stripped free of lignin which is why it burns so easily) rather it tends to smolder (i.e. logs in a fire), so fires would leave large amounts of charcoal rather than their usual main byproducts: carbon dioxide,carbon monoxide (at lower burning efficiencies) and water. Secondly, lignin is very hard to digest, even fungus/bacteria today have a hard time digesting it. 300 million years ago, the decay rate was practically zero. In summary, pretty much all of todays coal comes from plants which, millions of years ago, died and were buried without ever going through the process of decay.
What's even cooler though is that during this time gigantic insects roamed the earth https://en.wikipedia.org/wiki/Meganeura which is believed to be related to the faster metabolic rates that high oxygen content allows.

ELI5

01 Jun 2017 20:22

How do seeds know which way is up?

ELI5

30 May 2017 13:01

There is a global unified postal service body called the Universal Postal Union . The Union creates a framework and standards so that ALL countries can exchange mail freely without forming individual contracts with every other country.
When one pays for the postage for international mail, a portion of the money goes to the home country's postal service and a portion goes to the destination's postal service. The portion of money exchanged depends on how much mail (in weight) each country is exchanging. This is set up so that the destination country receives money for delivering the postage. Countries that receive more mail annually get less money per kilogram of mail.
The fee paid to the destination county is called a terminal due.

ELI5

30 May 2017 12:34

This is because muscle cells (also called muscle fibers) don't divide, and cancer is most common in cells that divide a lot. Dividing cells are primed for cancer because: 1) a lot of the machinery needed to divide rapidly is already present in the cell so not a lot extra is needed to make it grow uncontrollably into a tumor/cancer 2) the more a cell divides the more chances it has to make errors. DNA replication isn't perfect, and over time these errors can accumulate into dangerous mutations (this is also why cancer is more common in the elderly) This is why we see a lot of cancer in tissues with a high "cellular turnover" rate - skin, liver, colon, etc. Cells that never divide (muscle fibers, neurons) almost never get cancer. Brain cancer is usually caused by a special type of brain cell that can divide (but not signal) call neuroglia, which forms the cancerous "glioma." Bonus biology fact - because muscle cells fibers don't divide, you have the same number your whole life. Arnold Schwarzenegger has the same number of muscle fibers now as he did as a baby, they're just more packed with the good stuff. Source - biochemistry major, medical researcher.

ELI5

29 May 2017 21:03

Microwaves don't really heat food itself, they mostly heat the water inside food. But microwaves don't heat the water evenly. It gets heated in little sections, and those hot parts spread heat to all the cold ones. That takes time though. When food snaps but doesn't get hot its because the water in those hot parts started boiling (that's the sound) but it hasn't been long enough for the heat to spread out (that's why its cold). This is why packages say to let the food sit for a few minutes after cooking. Or you can run the microwave a few seconds on and a few seconds off to spread the cooking time out, which is the same exact thing the "power" setting will do.

ELI5

29 May 2017 20:57

"I actually worked in TV before computers. We would make the titles with press-on letters (I forget the brand name) and shoot them with a camera. The title camera would be combined with the live camera in a device called a "luma key" that would switch the live camera off and the title camera on everywhere that the lettering appears, based on the brightness. This was with monochrome cameras. With color cameras there was a device called a "chroma key" that would switch based on hue, usually tuned to blue. The same device was used for example to put graphics behind the weather man. You had to be careful the talent didn't wear any blue clothing."

ELI5

29 May 2017 20:44

Imagine you had a ping pong ball, and you filled it with cool whip. Now shrink that whole thing down to the size of a fly. Now imagine you threw that tiny little shell full of goop at the wall. Even if you threw it as hard as you could, it's still soooo tiny and soooo tough and bouncy on the outside that it'll just bounce off.
Flies are super tiny, and have a shell just like that ping pong ball, but with little flexible, foldable wings. And just like a fly, if you use a slingshot instead of your hand (a moving car instead of a window) you might just get it to pop.

Flies have an exoskeleton that's incredibly tough and hard in some spots, and just flexible enough to be springy and bouncy in others. Just like that ping pong ball, they've got a shell that's good at taking a bit of a hit and bouncing off instead of just squishing like a worm (which doesn't have that tough shell).
The fact that they're so small helps in a couple different ways as well. For one, we think they're flying super fast, but it's really just because they're tiny. If you look at a massive airplane, it might be moving at 500 miles per hour but still looks like it's just crawling along across the sky. Houseflies look fast, but I asked Google and they only go about 5 miles per hour. That means a baseball pitcher can throw a fastball 20 times as fast as a housefly flies.
Not only are they actually super slow (if you don't let the size trick you), they also weigh almost nothing. Like, it would take about 200 flies to add up to the weight of a single ping pong ball, according to some quick Googling/converting.
So your ping pong ball full of cool whip is actually super tough, reaaally slow, and unbelievably lightweight, meaning that dumb little fly was designed to fly into the window several thousand times before it finds the opening. Evolution at work.

ELI5

01 Jun 2017 20:28

Since millions of years ago there was a much higher oxygen content, did fire behave any differently?

ELI5

01 Jun 2017 20:22

All plants can sense the direction of the gravitational field and orientate themselves accordingly. This is called geotaxis. In mature plants, phototaxis (growing towards the light source) overrides the gravitational impulse for the stalk and leaves, but the roots - and the seed while it is underground - rely on gravity for orientation.
The mechanism is thought to be based on either the protoplasm (the living substance inside a cell) exerting a greater pressure on the cell walls at the bottom, or starch grains within the cells settling at the bottom. One or both of these cues influence the production of plant growth hormones that cause the plant to 'steer' as it grows.

Details for nerd 5 years old:
They have starchy components (amyloplasts) in some of their cells that are heavier than the cytoplasm, making them sediment at the bottom of the cell. A hormonal growth signal then emanates in the direction of the part of the cell where the amyloplasts accumulate (i.e. down).
You can see this for yourself by tipping over a fast-growing potted plant. The side of the stem facing down will grow faster, causing the shoot to gradually bend upright again. Plants use the same mechanism - uneven distribution of growth hormones in response to sensory input - when they grow toward light, etc.

ELI5

30 May 2017 13:01

When sending a letter abroad, how does the receiving country's mail service get paid for their work?

ELI5

30 May 2017 12:34

Why is heart cancer so rare?

ELI5

29 May 2017 21:03

Why sometimes when you put food in the microwave you hear lots of sparking sounds, then take it out, and your food is still cold/warm?

ELI5

29 May 2017 20:57

How did television studios make words like show titles appear on screen before computers?

ELI5

29 May 2017 20:42

How do flies constantly fly into hard objects at high speeds(walls, doors, windows, etc) but never manage to get hurt?