Ancient Egypt is one of the places where human civilization first really started to thrive.
Which might seem a little surprising, considering that over 95 percent of the country is desert.
But in between the expanses of the Sahara Desert is the Nile River. Now,
you might expect the banks of this river to be more sandy desert, but it turns out the
Nile River is lined with miles of a lush green landscape. This fertile farmland is
perfect for growing crops, and is part of why the Ancient Egyptian civilization was able to thrive.
So, how did the area around this river become so different from the desert it runs through? We know
that soil is different from wet dirt or sand, so it can't just be because of the river... right?
Today, we're going to explore the geological processes that
made the Nile River Valley into flourishing farmland, even in the middle of the desert.
By the end of this lesson, you should be able to identify causes of erosion,
explain how the processes of erosion and deposition are connected, and explain the
changes to earth's surface that erosion and deposition cause. Let's get started!
In our last lesson, we learned about the processes of weathering and erosion.
Weathering is when natural forces break rocks down. And erosion is when these forces move
them across the Earth's surface. For now, we're going to mostly focus on erosion.
Erosion is a natural process that is part of the rock cycle, and there are a few different
ways it can happen. The main causes are when wind blows rocks around, when moving water
from rainfall or streams carries rocks away, when ice carries rocks along with a glacier,
or when gravity simply makes rocks fall to somewhere else. Now you might be thinking,
okay so a couple of pebbles move around, what's the big deal about erosion? Pause the video here,
and write down why you think erosion might be an important geological process in your guided notes.
Remember, when we describe geological processes, we're talking about things that are slow,
but constant. Let's say erosion results in only five or six rocks moving off a mountain
every day. At the end of a year, that's about 2,000 rocks. After a hundred years
it's 200,000 rocks. After a long enough time, it can literally move mountains.
Different kinds of erosion have played a part in shaping some of Earth's most unique land forms
like the Grand Canyon, the Norwegian Fjords, Arches National Park, and the Matterhorn.
So we've seen what happens when erosion removes rocks and sculpts landforms, like these. But the
question is, where do they end up? That's where our next process comes in. Erosion is followed
by another process called deposition, which is when eroded rocks and sediments are deposited
and settle somewhere new. So while erosion shapes the Earth's surface by carving away
pieces of the land, deposition shapes it by dropping off rocks that create new landforms.
Beaches are created by the deposition of sand - rocks and shells that were eroded by the ocean.
Sand dunes are rolling hills of sand deposited by wind. And river deltas are triangular landforms
made when a river deposits the sediment it has eroded before emptying into another body of water,
which, it turns out, is what makes the Nile River delta so perfect for growing crops.
After winding its way through Africa for over 4,000 miles, the Nile River erodes
tons of rocks and minerals. At the end of its journey, when the Nile is emptying into
the Mediterranean Sea, it deposits these rocks and minerals along the river delta.
When it floods, these same minerals are deposited along the banks of the river as well. As a result,
the soil along the Nile River is great for growing crops, even though it's in the middle of
a desert. That's just another example of the many processes that shape the Earth's surface at work.
So, let's review what we learned today. You now know that erosion is caused by natural
forces like wind, water, ice, and gravity. Erosion and deposition are closely connected processes,
and both of these processes change Earth's surface by creating or reshaping landforms.
We've learned a ton about the processes that shape the planet Earth. So be sure to put your
new knowledge to good use with the games and extension activities to go with this lesson.
And remember - in Earth Science, as in life, you rock! See you next time!