1Hi, it's Doug.
2I didn't grow up anywhere near an ocean,
3but now as an adult, I live not far from one.
4That's the Pacific Ocean behind me.
5And I can tell you, if you've never been swimming in the ocean and accidentally gotten a mouthful of ocean water,
6it's so salty tasting.
7Now, it's never a great idea to drink any kind of water directly from an ocean or lake.
8There can be germs in it.
9But you can try ocean water for yourself at home
10by taking a few teaspoons of salt and dissolving it in a glass of water.
11Give it a try.
12Someone named Ali has a question about the ocean.
13Let's give her a call now.
14Hi Doug.
15Hi Ali.
16I have a question for you.
17Why is the ocean salty?
18That's a great question.
19One thing that's really weird is why the oceans are salty,
20but other water like lakes and rivers aren't salty at all.
21You might know that we call the water in lakes and rivers fresh water.
22Not that you can drink it directly.
23You still want to boil it or clean it before drinking.
24But water from lakes and rivers doesn't taste salty the way the ocean does.
25In fact, when scientists are studying any of the water that they find on Earth,
26that's one of the first things they do.
27They figure out is it salt water like from the ocean or is it fresh water like from lakes and rivers.
28So why is the water that's in the ocean different from the water that's in lakes and rivers?
29Why is the ocean water salty?
30Did a bunch of salt somehow get dumped into the ocean or something?
31Do you have any ideas?
32Why do you think the ocean is salty, but lakes and rivers aren't?
33Why does the water in the ocean have salt in it?
34I have to tell you, this is a tough mystery to solve.
35For a long time, very few people had any ideas at all.
36But today, we do have some ideas based on clues that people like scientists have noticed and discovered.
37Scientists have developed special tools and equipment
38that they can use to measure very small amounts of things.
39They discovered something really surprising.
40Even though the water in lakes and rivers is what we consider fresh water,
41when they tested the water and checked very carefully,
42they found out that this water actually does have a teeny tiny amount of salt.
43Not enough to where you'd be able to notice it if you tasted it.
44But the water in lakes and rivers is a little bit salty,
45just a little bit.
46In fact, every place they look,
47it doesn't matter if it's the tiniest pond or stream,
48there's still a little tiny bit of salt in the water.
49There's one exception, and that's this:
50rainwater.
51When it rains, that water (the water falling from the sky) has no salt in it at all.
52Even rain that falls on the ocean.
53There's zero salt in the raindrops.
54So rainwater is 100% completely fresh water.
55But here's the thing.
56Scientists discovered that once rainwater hits the ground,
57like when it starts to form puddles
58or when it trickles down into streams and rivers,
59that's when it starts to become a little bit salty.
60So then, there must be something about the ground itself
61which makes the water in lakes and rivers become just a tiny bit salty.
62And there is.
63Geologists are scientists who study the rocks and soil that the ground is made of.
64They've been able to figure out that most rocks and soil contain tiny amounts of salt.
65When rainwater lands on the ground, it absorbs some of that salt.
66As that rainwater trickles into lakes and rivers,
67it carries the salt with it.
68This is why water in lakes and rivers has a little tiny amount of salt.
69But rain itself, when it's falling, has no salt
70since it hasn't come in contact with the ground yet.
71But then why does the water in the ocean have so much more salt than the water in lakes and rivers?
72That's the big question.
73A question that scientists who study the ocean still aren't completely sure they know the exact reason.
74But if you look at a map and you trace your finger along the many rivers you see on the map,
75you can see that most rivers and even some lakes connect to the ocean.
76Since rivers and lakes are located on the continents or land,
77which is higher up than the ocean,
78the water in the rivers and lakes usually flows down into the ocean.
79Even though river and lake water only carries a tiny amount of salt,
80if that water has been flowing for years and years down into the ocean,
81all that salt that it does carry just keeps getting added to the ocean over and over,
82where it probably never leaves.
83We think this might be one big reason why the ocean is so much more salty than all the other water on Earth.
84That's all for this week's question.
85Thanks, Ali, for asking it.