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ONE STRANGE ROCK

6 THINGS THAT MAKE LIFE ON EARTH POSSIBLE

Earth is well equipped as a planet and ideally placed in our solar system and galaxy to support life as we know it. The product of some 4.6 billion years of cosmic construction, our planet is flush with life thanks to a fortuitous set of conditions.

BY MANUEL CANALES, MATTHEW W. CHWASTYK, AND EVE CONANT

MANUEL CANALES, MATTHEW W. CHWASTYK, Soren walljasper, ryan t. williams, ngm staff; SEAN MCNAUGHTON
art: ANTOINE COLLIGNON, tomÁŠ müller

Sources: PETER D. WARD, University of Washington; Kate Maher, Stanford University; Karina A. YAGER, NASA Goddard Space FLight Center; jason Barnes, University of IdahO, GUILLERMO GONZALEZ, BALL STATE UNIVERSITY; MICHAEL GOWANLOCK, NORTHERN ARIZONA UNIVERSITY; ICARUS; ASTROBIOLOGY; NASA/JPL; INTERNATIONAL JOURNAL OF ASTROBIOLOGY

20,000

light-years

10,000

light-years

Core

YOU ARE HERE

SOLAR SYSTEM

Proxima Centauri

AD Leonis

Eta Cassiopeiae A, B

Altair

Eta Cassiopeiae A, B

Altair

SUN

Procyon A, B

Alpha Centauri A, B

Sirius A, B

Delta Pavonis

SUN

Relative size

of the Earth

Solar flare

neptune

Uranus

sun

earth

Mercury

About 93 million miles

from Earth to Sun

venus

WE HAVE A BIG MOON TO

STABILIZE OUR AXIAL WOBBLE

moon

earth

The moon is a

relatively large

2% of the Earth’s

volume.

1

Our location is far from

MANY HAZARDS

The solar system is comfortably nestled in a safe harbor

between major spiral arms, and its nearly circular orbit helps

it avoid the galaxy’s perilous inner regions. There are

relatively few stars near the sun, reducing risks to Earth

from gravitational tugs, gamma-­ray bursts, or collapsing

stars called supernovae.

10,000

light-years

20,000

light-years

Core

YOU ARE HERE

SOLAR SYSTEM

Proxima Centauri

AD Leonis

Eta Cassiopeiae A, B

Altair

SUN

Procyon A, B

Alpha Centauri A, B

Sirius A, B

Delta Pavonis

2

Our SUN IS A STABLE AND LONG-

LASTING STAR

Stars more massive than the sun burn hotter and usually

don’t live long enough for planets to develop life. Less

massive, younger stars are often unstable and are prone to

blasting their planets with bursts of radiation.

SUN

Relative size

of the Earth

Solar flare

3

we’re at just the right

distance from the sun

Earth orbits in the so-called Goldilocks zone, where the planet

receives enough energy to allow water to exist as a liquid

on its surface. Too far, and the vital compound stays locked

up as ice. Too close, and the water would rapidly

evaporate into the atmosphere.

neptune

Uranus

sun

earth

SATURN

Mercury

About 93 million miles

from Earth to Sun

venus

4

we have the right stuff to

host a dynamic core

The interstellar cloud of gas and dust that gave rise to

Earth contained enough radioactive elements to power a

churning core for billions of years. This creates a magnetic

field that protects the planet from

dangers like solar flares.

Currents in Earth’s molten

outer core generate our

magnetic field.

earth

5

we have A BIG MOON TO

STABILIZE OUR AXIAL WOBBLE

Earth is tilted with respect to the sun, and teeters as it spins.

This tiny wobble can shift the climate from hot to icy every

41,000 years—and might vary more without the

moon’s stabilizing pull.

moon

earth

The moon is a

relatively large

2% of the Earth’s

volume.

1

Our location is far from

MANY HAZARDS

The solar system is comfortably nestled in a safe harbor

between major spiral arms, and its nearly circular orbit helps

it avoid the galaxy’s perilous inner regions. There are

relatively few stars near the sun, reducing risks to Earth

from gravitational tugs, gamma-­ray bursts, or collapsing

stars called supernovae.

20,000

light-years

10,000

light-years

Core

YOU ARE HERE

SOLAR SYSTEM

Proxima Centauri

AD Leonis

Eta Cassiopeiae A, B

Altair

SUN

Procyon A, B

Alpha Centauri A, B

Sirius A, B

Delta Pavonis

2

Our SUN IS A STABLE AND LONG-

LASTING STAR

Stars more massive than the sun burn hotter and usually

don’t live long enough for planets to develop life. Less

massive, younger stars are often unstable and are prone to

blasting their planets with bursts of radiation.

SUN

Relative size

of the Earth

Solar flare

3

we’re at just the right

distance from the sun

Earth orbits in the so-called Goldilocks zone, where the planet

receives enough energy to allow water to exist as a liquid

on its surface. Too far, and the vital compound stays locked

up as ice. Too close, and the water would rapidly

evaporate into the atmosphere.

neptune

Uranus

sun

earth

Mercury

SATURN

About 93 million miles

from Earth to Sun

venus

4

we have the right stuff to

host a dynamic core

The interstellar cloud of gas and dust that gave rise to

Earth contained enough radioactive elements to power a

churning core for billions of years. This creates a magnetic

field that protects the planet from

dangers like solar flares.

Currents in Earth’s molten

outer core generate our

magnetic field.

earth

5

we have A BIG MOON TO

STABILIZE OUR AXIAL WOBBLE

Earth is tilted with respect to the sun, and teeters as it spins.

This tiny wobble can shift the climate from hot to icy every

41,000 years—and might vary more without the

moon’s stabilizing pull.

moon

earth

The moon is a

relatively large

2% of the Earth’s

volume.

6

we have an ozone layer to block

harmful rays

Ancient plantlike organisms in the oceans added oxygen to the

atmosphere and created a high-altitude layer of ozone that

shielded early land species from lethal radiation.



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