2019-07-01_Discover

NORTH AMERICAN

SOUTH

AMERICAN

PACIFIC

Nazca

Cocos

Caribbean

Juan de Fuca

Easter

Juan Fernandez

Scotia

Shetland

Galapagos

Rivera

Altiplano

Northern

Andes

Panama

P

L

AT

E

S:

M

A

R

K

G

A

R

L

IC

K

/S

C

IE

N

C

E

S

O

U

R

C

E

.^ M

A

P

:^ A

L

IS

O

N

M

A

C

K

E

Y

/D

IS

C

O

V

ER

40 DISCOVERMAGAZINE.COM

EARTH IS ACTION-PACKED. Even if there were zero life

on our planet, the place would be full of birth and death,

marriage, breakup and even a little dirty dancing. That’s

all thanks to the lithosphere, a solid layer of crust and

part of the upper mantle that’s broken into more than

a dozen slabs, or plates, of varying sizes. These pieces,

divided between older continental crust and younger

oceanic crust, ride atop the gooey asthenosphere, a

semiliquid layer of magma and partly melted rock.

Most of us may think of Earth’s cracked and creep-

ing crust only when we hear of a catastrophic event

caused by it, such as an earthquake or volcanic erup-

tion. But the puzzle pieces of the lithosphere are always

in motion, slamming against one another, grinding

past or getting shoved under another slab. More than

a mere geological mosh pit, the plates play a key role in

climate and evolution.

Our planet’s big, slow square dance.

BY GEMMA TARLACH

Plate

Te c tonic s

CONTINENTAL: Crust that’s older and thicker,

made of lighter-weight rock.

OCEANIC: Younger and thinner, oceanic crust

is made of relatively heavier rock.

CONVERGENT: Where plates smash together,

resulting in deformation or destruction of

one or more plate edges. When one plate

sinks below another, forcing it back down to

Meltytown, it’s called subduction. This usually

involves a heavier oceanic plate being shoved

below a lighter continental plate. Examples:

the Izu-Bonin-Mariana subduction zone (where

the Pacific Plate is being pushed below the

Philippine Plate, creating the deepest oceanic

trenches in the world) and the Himalayan

mountain range (where the Eurasian and Indian

continental plates collide, crumpling up).

Types of Plates Types of Boundaries

CO

NTINENTAL

PL

A

T

E

O

C

E

A

N

IC

(^) P
LA
TE
Nearly all
tectonic
action occurs
at plate
boundaries.
Smaller plates
may get
worn away
completely
over time, but
the centers,
or cratons,
of larger
continental
plates remain
stable — they
include the
oldest rocks
on the planet.
Sources: USGS This Dynamic Planet, NASA, Peter Bird
EARTH'S CRACKED CRUST
EVERYTHING
WORTH
KNOWING