Zicoflex The biological and
geological future of
Earth can be
extrapolated based
upon the estimated
effects of several
long-term influences.
These include the
chemistry at Earth's
surface, the rate of
cooling of the
planet's interior, the
gravitational
interactionswith
other objects in the
Solar System, and a
steady increase in
the Sun's luminosity.
An uncertain factor
in this extrapolation
is the ongoing
influence of
technology
introduced by
humans, such as
climate engineering,
[2] which could cause
significant changes
to the planet.[3][4]
The current
Holocene extinction
[5] is being caused by
technology[6] and
the effects may
last for up to five
million years.[7] In
turn, technology
may result in the
extinction of
humanity , leaving
the planet to
gradually return to a
slower evolutionary
pace resulting solely
from long-term
natural processes.[8]
[9]
Over time intervals
of hundreds of
millions of years,
random celestial
events pose a global
risk to the
biosphere, which can
result in mass
extinctions. These
include impacts by
comets or asteroids
with diameters of
5–10 km (3.1–6.2 mi)
or more, and the
possibility of a
massive stellar
explosion, called a
supernova, within a
100-light-year radius
of the Sun, called a
Near-Earth
supernova . Other
large-scale geological
events are more
predictable. If the
long-term effects of
global warming are
disregarded,
Milankovitch theory
predicts that the
planet will continue
to undergo glacial
periods at least until
the Quaternary
glaciation comes to
an end. These
periods are caused
by eccentricity, axial
tilt, and precession
of the Earth's orbit.
[10] As part of the
ongoing
supercontinent
cycle , plate tectonics
will probably result in
a supercontinent in
250–350 million
years. Some time in
the next 1.5–
4.5 billion years, the
axial tilt of the Earth
may begin to
undergo chaotic
variations, with
changes in the axial
tilt of up to 90°.
During the next four
billion years, the
luminosity of the
Sun will steadily
increase, resulting in
a rise in the solar
radiation reaching
the Earth. This will
result in a higher
rate of weathering
of silicate minerals,
which will cause a
decrease in the level
of carbon dioxide in
the atmosphere. In
about 600 million
years from now, the
level of CO 2 will fall
below the level
needed to sustain C3
carbon fixation
photosynthesis
used by trees. Some
plants use the C4
carbon fixation
method, allowing
them to persist at
CO2 concentrations
as low as 10 parts
per million. However,
the long-term trend
is for plant life to die
off altogether. The
extinction of plants
will be the demise of
almost all animal life,
since plants are the
base of the food
chain on Earth.[11]
In about one billion
years, the solar
luminosity will be
10% higher than at
present. This will
cause the
atmosphere to
become a "moist
greenhouse",
resulting in a
runaway
evaporation of the
oceans. As a likely
consequence, plate
tectonics will come
to an end, and with
them the entire
carbon cycle.[12]
Following this event,
in about 2−3 billion
years, the planet's
magnetic dynamo
may cease, causing
the magnetosphere
to decay and leading
to an accelerated
loss of volatiles
from the outer
atmosphere. Four
billion years from
now, the increase in
the Earth's surface
temperature will
cause a runaway
greenhouse effect,
heating the surface
enough to melt it. By
that point, all life on
the Earth will be
extinct.[13][14] The
most probable fate
of the planet is
absorption by the
Sun in about
7.5 billion years,
after the star has
entered the red
giant phase and
expanded to cross
the planet's current
orbit.
Human
influence
Main articles:
Conservation biology,
Global warming, and
Human impact on the
environment
Humans play a key
role in the biosphere,
with the large
human population
dominating many of
Earth's ecosystems.
[3] This has resulted
in a widespread,
ongoing mass
extinction of other
species during the
present geological
epoch, now known
as the Holocene
extinction. The
large-scale loss of
species caused by
human influence
since the 1950s has
been called a biotic
crisis, with an
estimated 10% of
the total species
lost as of 2007.[6] At
current rates, about
30% of species are
at risk of extinction
in the next hundred
years.[15] The
Holocene extinction
event is the result
of habitat
destruction, the
widespread
distribution of
invasive species,
hunting, and climate
change.[16][17] In the
present day, human
activity has had a
significant impact on
the surface of the
planet. More than a
third of the land
surface has been
modified by human
actions, and humans
use about 20% of
global primary
production.[4] The
concentration of
carbon dioxide in the
atmosphere has
increased by close to
30% since the start
of the Industrial
Revolution.[3]
The consequences
of a persistent biotic
crisis have been
predicted to last for
at least five million
years.[7] It could
result in a decline in
biodiversity and
homogenization of
biotas, accompanied
by a proliferation of
species that are
opportunistic, such
as pests and weeds.
Novel species may
also emerge; in
particular taxa that
prosper in human-
dominated
ecosystems may
rapidly diversify into
many new species.
Microbes are likely to
benefit from the
increase in nutrient-
enriched
environmental
niches. No new
species of existing
large vertebrates
are likely to arise
and food chains will
probably be
shortened.[5][18]
There are multiple
scenarios for known
risks that can have
a global impact on
the planet. From the
perspective of
humanity, these can
be subdivided into
survivable risks and
terminal risks. Risks
that humanity pose
to itself include
climate change, the
misuse of
nanotechnology, a
nuclear holocaust,
warfare with a
programmed
superintelligence, a
genetically
engineered disease,
or a disaster caused
by a physics
experiment.
Similarly, several
natural events may
pose a doomsday
threat, including a
highly virulent
disease, the impact
of an asteroid or
comet , runaway
greenhouse effect,
and resource
depletion. There
may also be the
possibility of an
infestation by an
extraterrestrial
lifeform.[19] The
actual odds of these
scenarios are
difficult if not
impossible to
deduce.[8][9]
Should the human
race become extinct,
then the various
features assembled
by humanity will
begin to decay. The
largest structures
have an estimated
decay half-life of
about 1,000 years.
The last surviving
structures would
most likely be open
pit mines, large
landfills, major
highways, wide
canal cuts, and
earth-fill flank dams.
A few massive
stone monuments
like the pyramids at
the Giza Necropolis
or the sculptures at
Mount Rushmore
may still survive in
some form after a
million years.[9][a]
Random
events
The Barringer Meteorite
Crater in Flagstaff,
Arizona, showing
evidence of the impact of
celestial objects upon
the Earth
As the Sun orbits
the Milky Way,
wandering stars
may approach close
enough to have a
disruptive influence
on the Solar System.
[20] A close stellar
encounter may
cause a significant
reduction in the
perihelion distances
of comets in the
Oort cloud—a
spherical region of
icy bodies orbiting
within half a light
year of the Sun.[21]
Such an encounter
can trigger a 40-fold
increase in the
number of comets
reaching the inner
Solar System.
Impacts from these
comets can trigger a
mass extinction of
life on Earth. These
disruptive
encounters occur at
an average of once
every 45 million
years.[22] The mean
time for the Sun to
collide with another
star in the solar
neighborhood is
approximately 3 ×
1013 years, which is
much longer than
the estimated age
of the Milky Way
galaxy, at ~1.3 ×
1010 years. This can
be taken as an
indication of the low
likelihood of such an
event occurring
during the lifetime
of the Earth.[23]
The energy release
from the impact of
an asteroid or comet
with a diameter of
5–10 km (3.1–6.2 mi)
or larger is sufficient
to create a global
environmental
disaster and cause a
statistically
significant increase
in the number of
species extinctions.
Among the
deleterious effects
resulting from a
major impact event
is a cloud of fine
dust ejecta
blanketing the
planet, which lowers
land temperatures
by about 15 °C
(27 °F) within a
week and halts
photosynthesis for
several months. The
mean time between
major impacts is
estimated to be at
least 100
million years. During
the last 540
million years,
simulations
demonstrated that
such an impact rate
is sufficient to
cause 5–6 mass
extinctions and 20–
30 lower severity
events. This
matches the
geologic record of
significant
extinctions during
the Phanerozoic Eon.
Such events can be
expected to
continue into the
future.[24]
A supernova is a
cataclysmic
explosion of a star.
Within the Milky Way
galaxy, supernova
explosions occur on
average once every
40 years.[25] During
the history of the
Earth, multiple such
events have likely
occurred within a
distance of 100 light
years. Explosions
inside this distance
can contaminate the
planet with
radioisotopes and
possibly impact the
biosphere.[26]
Gamma rays
emitted by a
supernova react
with nitrogen in the
atmosphere,
producing nitrous
oxides. These
molecules cause a
depletion of the
ozone layer that
protects the surface
from ultraviolet
radiation from the
Sun. An increase in
UV-B radiation of
only 10–30% is
sufficient to cause a
significant impact to
life; particularly to
the phytoplankton
that form the base
of the oceanic food
chain. A supernova
explosion at a
distance of 26 light
years will reduce the
ozone column
density by half. On
average, a
supernova explosion
occurs within
32 light years once
every few hundred
million years,
resulting in a
depletion of the
ozone layer lasting
several centuries.[27]
Over the next two
billion years, there
will be about 20
supernova
explosions and one
gamma ray burst
that will have a
significant impact on
the planet's
biosphere.[28]
The incremental
effect of
gravitational
perturbations
between the
planets causes the
inner Solar System
as a whole to
behave chaotically
over long time
periods. This does
not significantly
affect the stability
of the Solar System
over intervals of a
few million years or
less, but over billions
of years the orbits
of the planets
become
unpredictable.
Computer
simulations of the
Solar System's
evolution over the
next five billion
years suggest that
there is a small (less
than 1%) chance
that a collision could
occur between Earth
and either Mercury,
Venus, or Mars.[29]
[30] During the same
interval, the odds
that the Earth will
be scattered out of
the Solar System by
a passing star are
on the order of one
part in 105. In such a
scenario, the oceans
would freeze solid
within several million
years, leaving only a
few pockets of
liquid water about
14 km (8.7 mi)
underground. There
is a remote chance
that the Earth will
instead be captured
by a passing binary
star system,
allowing the planet's
biosphere to remain
intact. The odds of
this happening are
about one chance in
three million.[31]