Very Interesting!

How old could the average rock be, how young? Are most very old? How old?

This will depend a lot on where you are. As an example, lets take a look at a super simplified geologic map (a type of map that shows the type/age or rocks at the surface in an area) of the USA. The colors here are keyed to age (and rock type for some), so if you broke off a piece of bedrock in South Dakota (which is mostly green colored on this map), then there's a reasonable chance it's Cretaceous in age (so between 145-65 million years old, or Ma), but if you broke off a piece of bedrock in Maine, chances are it might be Silurian (443-419 Ma) or Devonian (419-358 Ma) . But even then, it will depend a lot on location, e.g. in South Dakota if you picked up a rock from within the Missouri River, then it could be the age of any rocks within the area upstream of the river as rocks are eroded and transported by rivers. Similarly, in Maine, if you picked up a rock from a glacial deposit left after the retreat of the Laurentide ice sheet at the end of the last glacial maximum, it could be a rock transported from somewhere in Canada (and likely be much older, as much of the bedrock in Canada is Precambrian). Finally, as an extreme example, if you went to Hawaii and to some areas that had recent lava flows in 2018 and chipped off a piece of that bedrock, the rock would be 2 years old and more generally, if you were on the big island of Hawaii, no rock would be much more than 1 Ma. In short, there is no unique answer and it will depend on where you are and what rock you're picking up, i.e. is it from the local bedrock or is it in a deposit that includes rocks moved by something like a river or a glacier.

How long does it take to make an average round rock? How does it happen?

Rounded rocks are indicative of transport, usually by water. Let's imagine the life of a rock. It starts out as intact bedrock that may fracture as it is pushed towards the surface. These fractures will allow for a piece of rock to break off, forming what we would call a clast, i.e. a piece of loose rock, but this clast will be very angular. Eventually, this clast will move down hill via a variety of processes (e.g. soil creep or mass wasting) and reach a river. It will still likely be pretty angular, but depending on how it moved down hill, some of the sharpest edges may have been broken off (forming smaller clasts, but also progressively softening the original form of the clast we're tracking). Once in the river, the clast will be transported down stream where this clast will be rolled or bounced along the bed of the river and bump into other clasts. This process will progressively round the rocks as sharp edges are preferentially broken off, but will also progressively decrease the size of the clasts as you move down stream. As for the timescales, this can vary a lot, but generally, we consider sediment transport times short compared to other timescales in geology (i.e. 100s to 100,000s of years), but as with the first answer, it really depends on the specific location/river system.

Finally, a point of clarification. When we talk about the age of a rock (whether it's intact bedrock or a loose clast) we mean the time at which the rock became rock (e.g. crystallized from a magma, or was deposited as sediment and lithified into rock). So if a 100 Ma piece of bedrock breaks off and gets rounded while being transported in a river and you pick it up, it's still a 100 Ma rock, i.e. the erosional process doesn't reset the age. Now, if this 100 Ma clast is deposited and formed into a sedimentary rock, we can talk about the age of the sedimentary rock (which will be younger than any of the clasts that make it up) but also the ages of the original clasts that make up this new sedimentary rock.

To add to the answer regarding crustal rocks, I thought you might find this link interesting. The earth is covered by some 70% ocean, and under most of that is Oceanic Crust, made up of geologically recent rocks.

An eyeballed average is around 60 million years for Oceanic crust.

Of course, continental crust has a much larger range of ages, stretching far back in time. Australia has a wide range of ages, as you can see here (note the numbers are millions of years), mostly in the past billion years - however, there are large areas that are 2.5 billion years old.

The top comment currently sums it up very well. I would just also like the add, a phrase commonly uttered among geologists is "The older the rock, the greater the chance it no longer exists." This is because on Earth most rocks eventually get weathered, eroded, or subductured beneath the crust and melted. This is why some places like Australia are so important to paleontological studies of early life on Earth, since the regional geology there caused massive rock uplift that let rocks as old as 3.5 billion years old still be preserved today. Along with evidence of microbial life, but this is still controversial depending among the scientific community.

At the youngest, an igneous rock can be several hours old if magma just solidified. Sedimentary rocks and metamorphic rocks, on the other hand, are formed by processes that take several million years, so they youngest they can be is several million years old. As far as the oldest rocks, they are 3.8 billion years old I believe, with individual crystals being even older. Rock ages will vary widely based on where you're located. Rocks near the center of a continent (called a craton), will be billions of years old, with rocks generally (but not always) getting younger as you get closer to the edges of the continent. This is because continents started as small volcanic island chains billions of years ago, and slowly accreted new land. Seafloor rocks are never older than 200 million years, since they are constantly being subducted and destroyed.

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Mechanical engineering PhD here with significant study in fluid mechanics.

Yes the fluid will move around internally, mostly due to any rotation of the bottle. It you rotate the bottle at all (i.e. anything other than perfect linear motion) the inner walls of the bottle will cause drag against the water that’s closest to the edge. But the water in the middle of the bottle will be stationary due to inertia. The difference in momentum (edges are moving, center is stationary) will cause internal currents.

Note that this can be due to even very small-scale rotations to the point that this will always happen in the real world.

If you don’t believe me... put some food dye in a full water bottle then seal it. Shake it up and you’ll see the food coloring move around very quickly.

If you’re more interested in this, two important concepts are “Laminar flow” and “viscous drag”.

Depends on what you consider to be movement.

The molecules that make up the water are constantly moving, that's pretty much the definition of a fluid.

Even if you don't shake it, the molecules still move, but if you add force, you'll change the direction of that internal movement.

But the "shape" of the water ,for lack of a better term, will always fit the bottle. In a perfectly rigid bottle, that shape wouldn't change.

It's similar to the fact you're always moving, even if you stand still, because the earth is always circling the sun.

EDIT: which means the water is moving through space at all times as well, shaken or stirred, doesn't matter.

Assuming a really perfect 100% fill with water and no air or empty space, there is pretty much zero movement.

There is something to be said about the water pressure being higher in the parts closer to the ground (because of the weight of the water above)

and also in the parts opposite the direction of any force being applied to the bottle while shaking (because it's being mushed against that side by the rest of the water)

BUT, water doesn't condense very much at all with these tiny pressure differences. So it wouldn't result in any detectable movement.

Tap a bottle on something hard
The water will will try to move, this create pressure
Change in pressure allows a phase change and the liquid can turn into gas
Now bubbles are created inside the liquid
Then water will rush to fill that void
This will create a shockwave that breaks the bottle.

https://www.youtube.com/watch?v=t8L-XjpOruc
https://en.wikipedia.org/wiki/Cavitation

Beware really long post: It depends on your physics model, are you considering the water as a "fluid system" or "water + bottle"?

Are you considering molecules chains?

Are you considering single atoms?

Are you considering single particles?

Assuming you are referring to the most basic model: "water in a bottle", well, kind of, since friction between the bottle and water, but since you said "100% full" yes and no: take a balloon, fill it up with water, it explodes after a certain point, so, 100% in """reality""" is almost unachivevable level of balance...

On a 100% assuming it's perfectly balanced, still depends on how you made it, glass bottle, plastic bottle, ballon bottle(?)... do you think it moves? It might, do you want it to not move? Then, personally would use an alluminum bottle to fill it to 100 with low pressure...(don't know if every molecules would move, but some of them certainly yes, since, if you shake it very very very fast, you can make the water boil)

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Listen, I'm gonna be honest with you. You only need to unplug things for about 10 seconds, before you plug them back in. You can often speed things up by pressing the power button and holding it for 1-2 seconds (this closes the circuits to things like fans and power LEDs, allowing any energy in the capacitors to bleed off faster).

But when some mouth breather calls tech support complaining about their computer being frozen and the poor schmuck on the other end has already had a half-dozen arguments that day with callers who insist upon pulling the plug out half a millimeter and then slamming it back in as if the flow of electricity through the overworked circuits of their device was directly responsible for each sluggish, strained beat of their plaque-encrusted heart, all because the plug is "too hard to get to" after they shoved it under their desk behind a box of antique porn magazines...

Well, 30 seconds begins to sound like a nice, round number. Just long enough to keep them honest, but not long enough to encourage them to regale you with their political opinions or anecdotes about their various medical conditions while they wait.

Edit: fixed a word.

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Glass and Aluminum are quite different from plastic.

Aluminum is made of matching atoms, its pretty much pure. Melt it down, cook off any impurities and you've got yourself fresh aluminum which is indistinguishable from the original. Making fresh aluminum is also ludicrously energy intensive so there's a lot of incentive to collect and recycle previously used aluminum

Plastic is tricky because not all plastics are created equal. In general, plastics are long spaghetti strands that all stick together to give you the nice plastic you want, they're polymers which means they're made from long strings of monomers that are connected together. When you recycle your plastics you break your spaghetti strands, after a couple rounds of recycling you have couscous instead of spaghetti which doesn't work at all.

Making it even harder, "plastic" encompasses a broad variety of materials and if you don't separate your #1 plastic from your #2 or #6 you don't get plastic you can reuse at the end, you just get mush with uncertain properties, and since there isn't a great way to separate plastics by material quickly it greatly adds to the cost of plastic recycling because you need a manual sorting stage early on.

You can bake a cake, but you can't rebake a cake in to a different cake.

A lot of plastics have their properties changed by being melted and won't cool to have the same properties the had before.

Plastics are produced using plastic resin which are tiny pellets of plastic. Resins vary drastically by industry and brand based on the type of plastics being used and colorant that is being added.

This makes recycling extremely complex and expensive. Plastic must be sorted by type HDPE, PPE, etc. and by color. The plastic is then reduced back into pellets based on type and then reproduced.

When recycled, plastic will have impurities and depending on the type and number of times the plastic has been recycled it will also be weaker (more brittle). Eventually plastic can no longer be recycled because it has become too weak from the process and will crack.

Ultimately, it is much cheaper for companies to not use recycled plastic and their packaging looks cleaner. There are biodegradable resins in the works but none that I’m aware of are completely biodegradable and as you’d expect they cost more.

Source: 6 years in product development for a hair care brand.

What makes it hard to recycle efficiently is what makes plastics very useful in the first place. It is cheap to produce, inert, strong (easy to make containers), durable.

To recycle plastics, economically, it has to be done at a low cost, degrade something inert (heat, chemicals, mechanical processing) and containers are volumetrically inefficient for transportation (end up delivering mostly air, unless they are pre-crushed properly).

Basically you're going against the very reasons they were useful in the first place.

why? well because unlike aluminum it's cheaper to make new plastic than to recycle it.

Unlike glass old plastic isn't needed to make new plastic. Modern float glass requies ground old glass in its manufacture and aside from that ground glass in itself is a useful commodety.

There's economic utility in recycling glass and aluminum none in plastic.

Carbon dioxide, CO2, is more soluble in water than most common gasses. The solubility of a gas is proportional to pressure, Henry's Law, and the Henry's Law constant for CO2 (3.4x10^(-2) mol /L-atm) is one to two orders of magnitude greater than for the other atmospheric gasses: 6.1x10^(-4) for nitrogen and 1.3x10^(-3) for oxygen. So you can dissolve more CO2 in a given amount of beverage than you can N2 or O2. But you could use other gasses, and I believe Guinness does just that, using N2.

Another reason may have to do with taste. When CO2 dissolves in water it forms carbonic acid, H2CO3. This is a weak acid, so it could give some zap to the flavor, although the phosphate buffers in soft drinks may override this. Perhaps a food scientist could address the effect on flavor.

Less common gasses would be more expensive of course, but could in principle be used. N2O (nitrous oxide) for instance, is nearly as soluble as CO2 (Henry's Law constant of 2.5x10^(-2) mol/L-atm.) This could make an interesting drink since N2O is commonly known as laughing gas.

Amateur beer and winemaker here weighing in to say that part of the answer is that carbonation occurs somewhat naturally.

Traditional fermented beverages like beer, champagne (and even nominally non alcoholic ferments like root beer and ginger ale) can be naturally carbonated as part of the brewing process. Yeast turns sugars into alcohol and produces CO2 as a byproduct. By traditional methods the drinks were sealed with residual sugars and live yeast present resulting in a carbonated drink at the time of serving. Carbonation was not necessarily a desired feature, but a consequence of the process.

Today, many commercially produced drinks will kill off the yeast and carbonate artificially. With artificial carbonation being the norm now, some beer breweries have actually turned to other gasses, notably nitrogen. This is usually done with porters and stouts, and I believe that Guinness was, if not the first brewery to do this, a major contributor to making this popular.

Traditional non-sparkling wines only lack carbonation as a result of the aging process. Yeast will eventually stop producing CO2 (and alcohol) when it consumes all available sugars or when the alcohol content gets higher than the yeast can tolerate. If left to age, the CO2 will eventually rise out of the wine. Home wine makers often employ either agitation or vacuum pressure to degas the wine faster.

Pre-industrial vessels were less airtight than modern kegs and bottles, so beers were likely less carbonated than they are now. With industrialization, standardization and commercial production we now have the expectation of very gassy beers and completely flat wines, but this wasn’t always necessarily the case.

From a neuroscience perspective, CO2 triggers taste receptors ( https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3654389/#R17 ) as well as pain receptors ( https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2993877/ ) which may give rise to the tingly sensation. I'm not sure how sensitive these receptors are to other gasses, but it is likely that they would not produce the same sensations we expect from carbonation.

CO2 is cheap and forms carbonic acid in water, which adds a bit of a bite to the drink.

You can get rid of that bite, and get smaller bubbles by using N2, which is common with many beers.

Also, it's pretty common to use "Beer gas" for beers on tap, which is a combination of CO2 and N2. See: https://air-source.com/blog/the-benefits-of-beer-gas-blends-the-perfect-pint/

It's because it reacts reversibly with water to make carbonic acid. You can drive that reaction forward under high pressure and store a lot more CO2 in a volume of water than you could of most other gases. And because the reverse reaction takes time, your drink keeps fizzing for minutes to hours rather than losing all the dissolved gas very quickly once you release the pressure. And the carbonic acid adds a nice tangy taste to the drink.

If they weren't toxic, you could probably use sulfur dioxide or chlorine or acidic nitrogen oxides for the same thing.

Air is normally an insulator, which doesn't allow electricity to flow through it. However, if there's a big enough voltage, it can rip electrons out of atoms in the air (called "ionization"). This creates a chain reaction: The free electron can knock out electrons from other atoms, ultimately creating a path of conductive plasma that the electricity can flow through. It's like an electric avalanche.

The reason it forms a jagged line is that it's a random process. It'll move into whatever direction the first ionized atom is, rather than moving in a straight line to the next best conductor it can hit.

In Jurassic Park Jeff goldbloom does this thing where how if you let a drop of water roll down your hand it will not follow a predictible path each time.

The charge follows the path of least resistance just like the water. It's very prone to small changes each mm, and this adds into a jagged unpredictable path.

Remember the right-hand-rule from physics?:

"The various shapes of electric arcs are emergent properties of non-linear patterns of current and electric field (https://en.m.wikipedia.org/wiki/Electric_arc)"

Because of the right-hand-rule, current never flows straight through an insulator like air. It will always curve in an Arc towards the nearest conductor, due to magnetic fields present. It's called Arcing.

afaik electricity travels through the path of least (air)resistance. The odds of that bychance being a straight line between the two points is astronomically small.

So out of curiosity, is it fair to say it has just as much of a chance to take a straight line as any other path, but there are infinitely more paths than the straight one, so the odds are against the straight path?

Airplanes have air breathing engines (edit: and wings). This is great, since it means they don't need to carry their own oxygen, but it's not as effective at producing thousands of tons of thrust with a smallish device and they can't run in space.

Rockets don't use air breathing engines (edit: or wings) because they're too heavy, not powerful enough, and don't work in space. As a result, they don't benefit in any way from being in the atmosphere, and since the atmosphere has air resistance they'd like to get out of it as quickly as possible - especially the lowest, thickest, parts of it.

You're right in the sense that in order to get into orbit, a rocket has to go sideways very, very fast. The International Space Station is whizzing along at over 17,000mph!

However, spacecraft in orbit can only get to (and stay at) such ludicrous speeds because there's no air resistance to slow them down. The ISS is a fairly low 250 miles from the ground, most satellites are much further up.

In order to use their fuel in the most efficient way possible, rockets go straight up to get to thinner atmosphere as fast as possible. Then they begin to turn sideways, and increase their lateral speed.

There have been experiments with so called spaceplanes. The problem with them is that in order to reach orbit and leave the atmosphere they need to get really high and fast. Using aerodynamics to fly really high is contrary to get really fast, because the higher you get, the thinner the air becomes, yet you're not nearly as fast as you need to be for orbit. So you need to accelerate more and more, but still are too low to neglect air resistance. The result is that you burn much more fuel in order to get fast enough than if you just puncture straight out of the atmosphere and start turning at sufficient height.

Planes have wings which generate lift, the wings do the lifting up part and the engine pushes, so push and lift.

Rockets have no wings and will simply push, to get them into orbit you need to point them upward. They then PUSHHHHH into orbit.

Technically they do eventually end up horizontal sort of like a plane. The entire point is to get high enough and go fast enough so you basically fall endlessly while the Earth curves away. This is how we make things orbit our planet.

Down at sea level the air is quite thick and gravity its most effective. Space rockets go sort of straight up (they tend to start turning over in an arc early on to start their horizontal acceleration) to get up to the thinner air as quickly as possible as they have limited fuel.

Rockets need to carry everything that makes them fly with them including oxygen to make the engines work. The issue there is it increases weight, which means the rocket needs to be bigger to hold more fuel to lift it, which increases weight, and so on. We get past the problem now by staging, where we throw away spent engines to reduce weight while in flight.

In theory starting higher is more efficient. There are projects being tested that would launch rockets from large, high flying aircraft. The problem is that these planes need to get up to altitude as well which restricts the size of the payload they can bring. You will not be launching a Mars mission from a Virgin Galactic in its current state.

Still, the dream is to make it as cheap and efficient as possible so more and more people can have access to the space industry.

The Circadian Rhythm is the "internal clock" of the human body. Many stimuli affect it (Habits, mental state, physical state, genetics, environmental factors, medication, etc).

One of the main components of it is a hormone called Melatonin, produced mainly in the pineal gland of the brain. It is mostly influenced by light (hence, using smartphones at night might cause insomnia and other sleep-related issues). Cortisol is also important in the alertness process (Waking up).

This process is also influenced by learning, i.e. the thing we call habit. If you wake up at a certain time for a period of time, the Circadian Rhythm will adjust.

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There are a lot of factors tgat play into it, but as far as I understand it is a mix of melotonin onset (dependent on light, caffeine intake, excersize,cortisol levels, food) and circadian rhythm. Adjustment of wake up time and sleep patterns doesnt happen overnight (thus being jetlag and adjustment period when you travel). Your sleep consists of light NREM, deep NREM and Rem sleep that normaly shows in a pattern if you have good sleep hygene (dont drink redbull before bed or stare at flourescent lights ie). So eventhough sometimes you go to bed way later, the body can sort of "skip" the parts of sleep, hence why the people with sleep apnea feel alway tired (they cant enter deep NREM sleep - cortisol levels may be too high), and tries again thd next day to adjust to the pattern of hormones and wake up cycle that you have created. Thus you can keep on waking up on the same schedule if you keep the same hormon cycle. When people are jetlag it is the only recommended time to take melotonin by sleep expert, because that is what essentially dictates the phases of sleep. To the people anecdotally talking about their uncle dad etc that keep on waking up in the morning years after they left their job: The body actually accrues sleep debt that cannot be repaid, its not like you can undersleep all week and then sleep all weekend and be good - no. The few e is production of other hormones that allow you to get into NREM sleep that happens once in middle of the night and once just before to u wake up, that can decline if you are cronically underslept. They decline with age, so if you were depriving yourself in your youth from sleep (up to 45 yrs old) your ability to get the sleep you need declines. It has been proven that chronicly underslept people - are more likely to develop alzheimers because of a build up of plaque (i forgot what its called) that usually gets removed from the brain during REM sleep. Anyways sleep is fascinating, and if you would like to know more I would highly reccomend Why We Sleep from Mathew Walker. If you dont have time to read/listen, google at least an interview with him, it is very interesting.

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No, there is a natural carbon cycle that has been in operation for hundreds of millions (if not billions) of years of Earth's history (the carbon cycle as it exists now, would have been very different / nonexistent before the large scale presence of photosynthesizing organisms). If you look at the different components, you'll see that they operate on different time scales (e.g. the 'deep carbon cycle' is operating on a much longer time scale than any of the surface portions). Beyond the temporal scale differences, the different components and the individual fluxes in the carbon cycle have changed through time (which is one of the primary mechanisms by which natural climate changes have occurred) through a variety of natural processes (e.g. major mountain building events can cause an increase in chemical weathering which removes carbon from the atmosphere and sequesters it carbonate rocks in the oceans, etc).

More to the point of the question, carbon stored in fossil fuels is not removed from this cycle, it's just transferred into a different part of the cycle. So no, there was no danger of ecosystem collapse without us (and in fact the opposite, by mining and injecting vast quantities of carbon into the atmosphere geologically instantaneously, we have seriously perturbed the natural carbon cycle and the climate, and thus are increasingly pushing many ecosystems dangerously close to collapse because of the rapidity of the changes).

Humans only add about 3% more carbon than the natural cycle emits but that’s enough to throw the balance right off. The parts per million in the atmosphere has been steadily growing since the industrial revolution.

So I saw a video a while ago that went into details about how the Earth has been losing carbon in its atmosphere for some time now.

When, according to this video, was Earth's atmosphere losing CO2? Prior to the industrial revolution its was 280 parts per million (ppm), now its around 415ppm. 10,000 years ago it was about 260ppm.

Here's a decent article from climate.gov on CO2 in the atmosphere which has a graph showing concentrations over the last 800K years. You can see it bounces around between about 175-300ppm, with the peaks and valleys following the course of the ice ages.

In small scale experiments, increased CO2 does accelerate plant growth. This is called CO2 enrichment or CO2 fertilization. Some industrial agriculture uses this technique to grow bigger plants in greenhouses faster.

But plants do not grow only on CO2, there are many other factors. For example, plants also require nitrogen to grow and nitrogen is often a limiting factor of plant growth (plants cannot extract nitrogen from the atmosphere). Additionally, plant growth and specifically crop yields are greatly affected by temperature: increase the temperature by 2 degrees and crop yields of certain types of plants will drop.

So, in a limited experiment where all variables are held steady except CO2 levels (and other required elements are abundant) increased CO2 helps plants grow. But increased atmospheric CO2 in the real world also has other side effects that may actually hurt plant growth.

The only time something happened whereby there was not enough carbon dioxide in the atmosphere was the Permian age. That was because trees were new and nothing could break down their cellulose at the time. However, trees are easily composted now by microbes that release their stored carbon when they rot. So there is no need for people to add extra carbon. The earth is quite full of it, thank you very much.

Your body does reabsorb the blood over time.

The risk of internal bleeding isn't because the blood in your body doesn't ever go away, it's because it may go unnoticed for too long or may not be stoppable without proper medical intervention.

Think of you blood vessels like roads. There are trucks on the road carrying stuff around, these are red blood cells. In the case of internal bleeding some trucks have gone off the road and are no longer working. A tow truck, white blood cell, shows up to break down the truck and recycle the parts. The tow truck can go off road if it needs to.

Blood is instead of plasma and cells (Plasma is the liquid that holds all the cells and hormones etc.) Plasma itself is absorbed easily back into the cells. The main reason that you see bruises, is the presence of RBCs.

After a while, many of the RBCs are broken down simply by not having nutrients and oxygen. The immune system also "devours" them by a mechanism called Phagocytosis, digests them, and puts the remains (mostly Amino Acids) back to use. The body is great at salvaging, and tries not to let anything go to waste!

If it is a small amount, it is reabsorbed by the body, if it is a large enough amount that it is pooling then you need a surgeon to suction it out for you. You don't need a lot of blood to be a problem, which is why 'internal bleeding' is an alarm to doctors. You can tolerate a bit, in fact many times the treatment is to keep you still so that it clots off on its own without surgical intervention, but if you have a big bleeder then a surgeon needs to go in and repair the bleed and suction the blood out. To a certain extend, you are somewhat 'leaky', which is why our blood clots so easily. The risk of dangerous bleeds is a side effect of the same drugs (aspirin, coumadin, etc) which prevent people from having heart/brain attacks. If you are kinda leaky already, you take a blood thinner, then you undergo some amount of physical trauma, this can be a potentially dangerous situation. You really don't want fluids 'pooling' in the body, in some cases (like around the heart) it can be life threatening.

I had an internal bleeding after an inguinal hernia operation. Why does internal bleeding hurt so much?