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A couple of days after the eggs are laid,they hatch,and the cycle begins again.And because we've never seen the adult eels returning up the fresh water rivers,we must assume that,having completed their long and roundabout journey,these amazing and mysterious creatures finally die there,in the same place where they were born. Goodbye, Elaine!It was a pleasure knowing you.

But it's assumed that they can follow some signs that they can detect,such as a thermal barrier between ocean currents or a salinity front,in order to return to the same area of the ocean where they were born.Because we don't even know exactly what happens during an eel's migration,we can only imagine what the actual breeding looks like.But the common hypothesis is that Elaine and thousands,or hundreds of thousands,of other eels gather in large, intertwined masses and release their eggs and sperm in a giant orgy known as panmixia.

As Elaine leaves fresh water for the ocean,she undergoes a shocking metamorphosis.Her eyes enlarge by about ten times,her skin gets thicker,and her fins get larger.These are most likely adaptations for their upcoming ocean travel,and Elaine seamlessly makes the transition from fresh to salt water,which would be toxic for most other fish.Once Elaine leaves the mouth of the fresh water streams,she will disappear completely from human view.No one has witnessed,or been able to follow,an adult eel on their migration,nor do we know how deep they spawn.

As a female eel,Elaine will be quite solitary for most of her life in the stream,eating whatever falls in the water:grasshoppers, crickets, small fish,insect larvae, frogs, baby birds,almost anything she can get her mouth around.And she will grow quite big,up to four feet long and weighing as much as thirteen pounds.We don't know exactly how fresh water eels know when it's time to return to the ocean,but something calls to them.And their fall migration is one of the largest unseen migrations on the planet.

But within a couple of days in fresh water,Eli's skin becomes pigmented a brownish-black,now looking more like that of an adult eel.You might notice that we haven't mentioned anything about Eli's gender yet.That's because this is only determined once an eel enters fresh water,though nobody is sure exactly how that happens.Most of the eels that stay in the estuaries and brackish water become males,while those that go upstream become females,growing up to two to three times bigger than their future mates.In this case,it turns out that Eli was actually short for Elaine.

Our eel, let's call it Eli,would begin as one of ten to twenty million tiny eggs,carried by a female eel,hatching into a transparent leaf-shaped thing that looks nothing like an adult eel.Eli starts to drift in ocean currents,predominantly the Gulf Stream towards either Europe or North America,depending on its particular species.Upon reaching the coast,Eli is about two inches long,looking more eely but still transparent,known at this stage as a glass eel.

And, unlike most migratory fish,such as salmon,which spawn in fresh water but live their adult lives in salt water eels of the genus Anguilla migrate in the opposite direction,spawning and breeding in oceans and seas,while spending most of their intervening time in fresh water.If we were to take one such fresh water eel and follow its life story,it would be born in the middle of the North Atlantic Ocean,about a thousand miles east of Bermuda.This area, called the Sargasso Sea,forms the western part of a subtropical gyre,a giant whirlpool in the middle of the ocean.

They're long and slithery,and they're not very colorful.But they do have a strange beauty of their own. Their sinuous, nocturnal movements through the water are mesmerizing to watch.And though they may resemble underwater snakes,eels are, in fact, a very interesting type of fish.There are several things about eels that make them unique besides their elongated shape and limbless bodies.For one thing,eels have the ability to breathe through their skin. Some can even leave the water and move over land for short periods.

Don't try any of the things you've seen on the internet or in movies!Don't try to capture and kill the animal that bit you,and don't use a tourniquet or knife on your wound.Most importantly, don't panic!Stay calm, and seek medical attention.Treatment will mostly depend on what species you encountered.But if you forget the distinctionbetween poison and venom,and tell the parademics that you were poisoned by a viper,they'll probably forgive you and treat you anyway.

Then, the little remipede closes in,dissolving away the exoskeleton of its prey and sucking out the juices.But poisons and venoms aren't always all bad.For thousands of years, humans have looked for ways to harness the power of these toxic compounds for good. Today, we have all sorts of medicines that come from toxins.The poison from cone snails is used as a painkiller.Many poisonous plants have been used to treat everything from malaria to irregular heartbeats.And scorpion venom might one day be used to treat heart disease.So, what should you do if something bites or poisons you?

Scientists are constantly finding new animals that employ toxins in weird, interesting ways.Recently, researchers discovered the very first venomous crustacean.Out of 70,000 species of crustaceans,only this one little remipede is venomous.Speleonectes tulumensis has figured out how to create a cocktail of toxins that it delivers through its tiny fangs.Scientists aren't totally sure how this venom works yet,but they think that it causes the unwitting victims' neurons to fire over and over and over again until it becomes paralyzed.

And some compounds can be poisons in one animal and venoms in another.Tetrodotoxin, a chemical 10,000 times more toxic than cyanide,is found in pufferfish,where it makes them poisonous.It's also found in the deadly blue-ringed octopus,where it's a venom delivered by bite.Some animals can even be both poisonous and venomous.Take the Asian tiger snake, for example.Not only does it have venom in its fangs but it also absorbs the toxins from the poisonous toads it eats,and then secretes those toxins from special glands on its neck,rendering it poisonous, too.

If the frog's poison reaches your heart,it can cause it to stop.The distinction between venom and poison is purely in the method of delivery.Poison has to be inhaled, ingested, or absorbed.Venom has to be injected into a wound.Chemically, venoms and poisons are both considered toxins,so a snake bite is venomous.A poison dart frog is poisonous.Brown recluse spiders are venomous.Lionfish and pufferfish are poisonous.

But you might get lucky!Snakes don't always decide you're worth wasting venom on. In fact, between 20 and 80% of snake bites are so-called "dry bites,"where the snake is just trying to send a message without actually killing you.You see, venom takes energy and resources for the snake to make,and they don't want to waste it on a warning shot.When it comes to poison,on the other hand,there's no warning shot.If you pick up a poisonous dart frog to admire its beautiful colors,you've already gotten deadly poison all over your hands.As it seeps into your skin and travels through your blood,the poison starts to interfere with your nerves,preventing your muscles from contracting.

Would you rather be bitten by a venomous snake or touch a poisonous frog?Wait, what's the difference between poison and venom, anyway?Let's say you have the misfortune to be bitten by a venomous rattlesnake.When it bites you,the snake will eject venomfrom little sacks behind its eyes,through its hollow fangs and into your flesh.That venom will then travel through your bloodstream and all over your body.In most cases, snake venom contains neurotoxins,proteins that can do all sorts of nasty stuff like make your muscles fire uncontrollably,burst your blood cells,and make you go completely numb.

Small planets like ours don't have enough gravity to hold on to much hydrogen or helium gas since both of those are very light.So, even though carbon, nitrogen, oxygen and so on made up only two percent of the gas cloud from which Earth was formed,these heavier elements form the bulk of our planet and everything on it.Think about this:with the exception of hydrogen and some helium,the ground you walk on,the air you breath, you,everything is made of atoms that were created inside stars.When scientists first worked this out over the first half of the 20th Century,the famous astronomer Harlow Shapley commented,"We are brothers of the boulders, cousins of the clouds."

That means that the gas it arose from had itself been enriched with many elements from supernova explosions since the universe began. So that's how the sun wound up with all the elements.It's still mostly hydrogen at 71 percent,with most of the rest being helium at 27 percent.But bear in mind that while the first stars were made up of hydrogen and helium alone,the remaining elements in the periodic table make up two percent of the sun.And what about Earth?Planets form as an incidental process to star formation out of the same gas cloud as the star itself.

Second, all the elements that had been accumulating in the core of the star,like carbon, oxygen, nitrogen, iron,as well as all of those formed in the supernova explosion,are ejected in to interstellar space where they mix with the gas that's already there.History then repeats itself.Gas clouds, now containing many elements besides the original hydrogen and helium,have higher density areas that attract more matter, and so on.As before, new stars result.Our sun was born this way about 5 billion years ago.

Over its lifetime,the fusion reactions in the core of a massive star will produce not only helium,but also carbon, oxygen, nitrogen and all the other elements in the periodic table up to iron.But eventually, the core's fuel runs out,leaving it to collapse completely.That causes an unbelievably powerful explosion we call a supernova.Now there are two things to note about how supernovas create elements.First, this explosion releases so much energy that fusion goes wild forming elements with atoms even heavier than iron like silver, gold and uranium.

Eventually, large dense gas balls formed,shrinking under their own gravity and consequently heating up on the inside.At some point, the core of such a ball gets hot enough that nuclear fusion occurs.Hydrogen atoms smash together to form helium,accompanied by a great release of energy,strong enough to counteract the shrinking force of the gravity.When the energy pushing out from the fusion reactions matches the gravity pulling all the gas inwards,an equilibrium occurs.From this a star is born.

It all started 14 billion years ago with an event we call The Big Bang,which resulted in a universe consisting of gas alone.There were no stars and no planets.The gas was made up only of atoms belonging to the simplest elements.It was about 75 percent hydrogen and almost all the rest was helium.No elements like carbon, oxygen or nitrogen existed.No iron, silver or gold.In some places, the density of this gas was slightly higher than in others. Due to gravity, those places attracted even more gas,which further strengthened the pull of gravity,which then drew more gas in, and so on.

All the material objects around you are composed of submicroscopic units we call molecules.And molecules in turn are composed of individual atoms.Molecules frequently break apart and then form new molecules.On the other hand,virtually all the atoms you come in to contact with through the course of your life,the ones in the ground beneath you,the air you breath, the food you eat,those that make up every living thing, including you,have existed for billions of years and were created in places very unlike our planet.How those atoms came about is what I want to share with you.