FUTURE OF THE EARTH
The future of our earth is completely depends on the sun.
As a result of steady accumulation of helium at the sun’s core, the sun’s total
luminosity will increase slowly. More
specifically, the luminosity of the sun will grow by 10% over the next 1.1
billion years and by 40% over the next 3.6 billion years. After 4.8 billion
years, when the sun becomes 67% more luminous than at present, the hydrogen
fuel at the core of the sun becomes exhausted. Thereafter the sun will continue
to burn hydrogen in a shell surrounding its core, until its luminosity
increases 121% of its present value. This marks the end of the sun’s main
sequence lifetime, and thereafter it will pass through the subgiant stage, and
then evolves into a redgiant.
TILL 1.1 BILLION YEARS FROM TODAY-
Now with the
increased surface area of the sun, the amount of energy emitted will increase.
The global temperature of the earth will climb because of the rising luminosity
of the sun; the rate of weathering of minerals will increase. This in turn will
decrease the level of carbon-di-oxide in the atmosphere. Within the next 600
million years from the present, the concentration of carbon-di-oxide will fall
below the critical threshold need to sustain
photosynthesis about 50 parts per
million. At that point the trees and the forest in their current form cannot
survive. However,
carbon fixation can continue at much
lower concentration, down to above 10 parts per million. Thus plants using
can be able to survive for at least .8
billion years to 1.1 billion years more. Currently
using plants represents about 5% of the
Earth’s plant biomass and 1% of its known plant species. For examples 50% of
all the grass species use the
photosynthetic pathway. When the levels of the
carbon-di-oxide fall down to the limit where photosynthesis is barely
sustainable the proportion of carbon-di-oxide in the atmosphere is expected to
oscillate up and down. This will allow the land vegetation to flourish each
time the level of carbon-di-oxide due to the tectonic activity and the animal
life. However, the long term trend is for the plant life on land to die off
altogether as most of the remaining carbon in the atmosphere becomes
sequestered in the earth. Loss of these most of the land plants result the
eventual loss of the oxygen. That leads to the death of animals. 1st
animals to be disappeared will be the large mammals. After that, small mammals birds,
amphibians, reptiles and finally the invertebrates. Though some insects and
reptiles may be survive along with the sea animals. More specifically we can
say most of the multicellular lifeforms and many of the eukaryotes
extinct. 1.1 billion years after today, mainly the prokaryotes exist in the
planet.
AFTER 1.1 BILLION YEARS FROM TODAY-
After 1.1 billion
years the luminosity of the sun grows by 10% of today. That makes the average
temperature of the global surface to 320k. The atmosphere will become a moist
greenhouse leading to a runaway evaporation of the oceans. And approximately
27% of the modern ocean will have been sub-ducted into the mantle. At this
point, the model of the earth’s future demonstrates that the stratosphere would
contain increasing levels of water. These water molecules will be broken down
through photo-dissociation by solar ultraviolet radiation, allowing hydrogen to
escape the atmosphere. We can call this time as the ocean-free era. During this
ocean-free era, there will continue to be reservoirs at the surface as water is
steadily released from the deep crust and mantle, where it is estimated there
is an amount of water equivalent to several times that currently present in the
earth’s oceans. Some water may be retained at the poles and there may be
occasional rainstorms, but most part of the planet would be a dry desert with
large dunefields covering its equator, resembling how Saturn’s largest moon
Titan looks like today. Even in this arid condition, earth may retain some
microbial, possibly even some multicellular life. Most of these microbial are
halophiles. However, the increasing extreme conditions will likely leads to the
extinction of the prokaryotes between 1.6 billion years to 2.8 billion years
from now, with the last of them living in residual ponds of water at high
latitudes and heights or in caverns with trapped ice; underground life,
however, could last longer. What happened next depends on the level of
tectonics activity. A steady release of the carbon-di-oxide by volcanic
eruption could eventually cause the atmosphere to enter a supergreenhouse state
like Venus. But without surface water, plate tectonics would probably come to a
halt and most of the carbonates would remain securely buried until the sun
becomes a red giant and its increased luminosity heated the rock to the point
of releasing the carbon-di-oxide. The loss of the oceans could be delayed until
two billion years in the future if the total atmospheric pressure were to
decline. A lower atmospheric pressure would reduce the greenhouse effect,
thereby lowering the surface temperature. This would occur if natural processes
were to remove the nitrogen from the atmosphere. Studies of organic sediments
have shown that at least 110 kilopascals i.e. .99 atm of nitrogen has been
removed from the atmosphere over the past four billion years; enough to
effectively double the current atmospheric pressure if it were to be released.
This rate of removal would be sufficient to counter the effect of the
increasing solar luminosity for the next two billion years. However, beyond
that point, unless most of the earth’s surface water has been lost by the time,
in which case the planet will stay in the same conditions until the starting of
the red giant phase. The amount of water in the lower atmosphere will have
risen to 40% and the runway moist greenhouse will commence when the luminosity
from the sun reaches 35-40% more than the current value, 3-4 billion years from
now. The atmosphere will heat up and the surface temperature will rise
sufficiently to melt surface rock. However, most of the atmosphere will be
retained until the sun has entered the red giant stage. And once the sun
entered the red giant phase, the changes from burning hydrogen at its core to
burning hydrogen around its shell, the core will start to contract and the
outer envelope will expand. The total luminosity will steadily increase over
the following billion years until it reaches 2730 times the sun’s current
luminosity at the age of 12.167 billion years. During this phase the sun will
experience more rapid mass loss, with about 33% of its total mass shed with the
solar wind. The loss of mass will mean that the orbit of the planet will
expand. The orbital distance of the earth will expand. The orbital distance of
the earth will increase to at most 150% of its current value. At the final
stage of the red giant phase of the sun (when the age of the sun will be 12
billion years), it is likely to expand to sallow both mercury and Venus,
reaching a maximum radius of 1.2 A.U (180,000,000 km). The earth will interact
tidally with the sun’s outer atmosphere, which would serve to decrease earth’s
orbital radius. Drag from the chromosphere of the sun would also reduce the
earth’s orbit. These effects will act to counterbalance the effect of mass loss
by the sun, and the earth will most likely to be engulfed by the sun. the
ablation and vaporization caused by its fall on a decaying trajectory towards
the sun will remove earth’s crust and mantle, then finally destroy it after at
most 200 years. Earth’s sole legacy will be a very slight increase (0.01%) of
the solar metallicity. Before this happens, most of earth’s atmosphere will
have been lost to space and its surface will consist of a magma ocean with
floating continents of metals and metal oxides as well as icebergs of
refractory materials with its surface temperature reaching more than 2,400K.
The drag from the solar atmosphere may cause the orbit of the moon decay. Once
the orbit of the moon closes to a distance of 18,470 km, it will cross the
earth’s Roche’s limit. Tidal interaction with the earth would then break apart
the moon, turning into a ring system. Most of the orbiting ring will then begin
to decay, and the debris will impact the earth. Hence, even if the earth is not
swallowed up by the sun, the planet may be left moonless and lifeless.
