Download UNIT 1, Chapter 1, Lesson 2

UNIT 1, Chapter 1, Lesson 2
The Maturing Earth
Directed Reading Assignment
Read pages 190-193
1. A substance made of two or more elements that have chemically combined is a
________________________.
2. There are two types of crust, ____________________________ and
____________________.
3. ________________________ crust is thinner and denser than
_________________________ crust because it has more __________________,
__________________________, and _____________________ in its
compounds. It more closely resembles mantle material than crust material since it
is created mainly through volcanic flows of lava from the mantle.
4. Continental crust is thickest where there are mountains. Here it can be as much as
____________________ km (that’s 62 miles) thick. The ocean crust is only about
_______________ km (3 miles) thick.
5. No one has ever drilled completely through the crust, but in places (such as
volcanoes) ___________________ rock pushes to the surface (in molten form),
allowing scientists to study the rock directly.
6. The crust and upper mantle consist or rock that is both solid and rigid (nonflexible). Together they form the _________________________, which is
cracked into pieces called __________________ ___________________.
7. The soft, flexible (plastic) region in the upper mantle is known as the
___________________________. Here, temperatures approach but rarely exceed
the melting point of the rock.
8. The ____________________ __________________ appears to be completely
liquid. The flow of liquid iron here is believed to be the source of Earth’s
magnetic field.
9. From the surface of the earth down to the center of the earth measures a distance
of about _____________________ km (that’s about 4000 miles).
10. The lower region of the mantle is called the ______________________. It
consists of strong, rigid, dense rock material.
Read pages 626-629
11. Scientists believe that the early atmosphere was a steamy mixture of
_______________ ________________ and __________________
_________________. Today, the atmosphere is a mixture of mostly
_________________ and ________________. Therefore, the atmosphere has
undergone many changes since earth formed.
12. Much of the ____________________ in our atmosphere came from volcanoes.
Most of the water vapor in the early atmosphere has ______________________
into liquid to form Earth’s first oceans. This was made possible as Earth’s surface
cooled to form a solid surface.
13. The early atmosphere did not have ____________________ to protect Earth from
ultraviolet radiation. This radiation helped break apart molecules of methane and
ammonia in our atmosphere, seeding the oceans with elements important to the
formation of life such as carbon, hydrogen, and nitrogen.
14. The first life forms on Earth were very simple and did not need ______________
to live. Rather, they changed most of the carbon dioxide into oxygen through the
process of __________________________.
15. By about 4 billion years ago, a global ___________________ covered the planet,
with the exception of a few small volcanic islands. As the outer layers cooled, the
temperature difference between the outer and inner earth created currents of rock
that began stretching and compressing the crust. In areas the crust gradually
thickened and slowly rose above sea level, forming Earth’s early
________________________. Eventually, the crust would separate into “plates”
and carry these together (in places) to form mountains and larger landmasses.