Earth Will Survive Global Warming, But Will We The notion
that human activity, or the activity of any organism, can affect Earth on a
planetary scale is still a hard one for many people to swallow. And it is this
kind of disbelief that fuels much of the public skepticism surrounding global
warming. A poll conducted last summer by the Pew Research Center
found that only 41 percent of Americans believe the burning of fossil fuels
causes global warming. But in a meeting this week in Paris, officials from 113
nations have agreed that a highly anticipated international report will state
that global warming was "very likely" caused by human activity. The idea that
biology can alter the planet in broad and dramatic ways is widely accepted among
scientists, and they point to several precedents throughout the history of
life. The mighty microbes Human-caused global
warming--also called "anthropogenic" global warming--is the latest example of
life altering Earth, but it is not the most dramatic. That title
probably goes to the oxygenation of Earth’s early atmosphere by ancient microbes
as they began to harness the power of sunlight through
photosynthesis(光合作用). Humans "are having a strong effect on
global geochemical cycles, but it does not compare at all to the advent of
oxygenic photosynthesis," said Katrina Edwards, a geo-microbiologist at the
University of Southern California (USC). "That was a catastrophic environmental
change that occurred before 2.2 billion years ago which wreaked its full wrath
on the Earth system." Edwards studies another way life impacts
the planet in largely unseen ways. She focuses on how microbes living on the
dark ocean floor transform minerals through a kind of underwater
power. "These microbes are completely off radar in terms of
global biogeochemical cycles," Edwards told Live-Science." We don’t consider
them as part of the Earth system right now in our calculation about what’s going
on, and we don’t consider them in terms of how the Earth system will move
forward into the future." These reactions are strongly
influenced by life and have been occurring for billions of years, for as long as
the oceans have been oxygenated and there have been microbes inhabiting the
seafloor, Edwards said. Creating Earth On land,
microbes, and in particular a form of bacteria called cyanobacteria (固氮蓝藻), help
keep soil in place and suppress dust. "We’d certainly have more
dust storms and it would not be anywhere as nice on Earth if they weren’t
around," said Jayne Belnap, a researcher with the United States Geological
Survey. Scientists believe the tiny life-forms performed the
same roles on early Earth. "One of the big problems for geologists is that, OK,
you have this big ball of rock, the soil is weathering out and you have these
ferocious winds. What in the world is holding the soil in place as it weathers
out of the rocks" Belnap said in a telephone interview. "Cyanobacteria are also
credited with that function." The microbes anchored soil to the
ground; this created habitats for land plants to evolve and eventually for us to
evolve. "They literally created Earth in a sense," Belnap said.
"Cyanobacteria are just like ’it’," she continued. "I’ve been telling
everybody to make a small altar and offer sacrifices every night. We owe them
everything." A snowball planet The mighty microbes
also triggered sudden climatic shifts similar to what humans are doing now.
Recent studies suggest that the proliferation of cyanobacteria 2.3 billion years
ago led to a sudden ice age and the creation of a "Snowball Earth."
As they carry out photosynthesis, cyanobacteria break apart water and
release oxygen as a waste product. Oxygen is one of the most reactive elements
around, and its release into the atmosphere in large amounts destroyed methane
(沼气),a greenhouse gas that absorbed the sun’s energy and helped keep our planet
warm. Some scientists think the disappearance of this methane
blanket plunged the planet into a cold spell so severe that Earth’s equator was
covered by a mile-thick layer of ice. Earth might still be
frozen today if not for the appearance of new life forms. As organisms evolved,
many developed the ability to breathe oxygen. In the process, they exhaled
another greenhouse gas, Carbon dioxide, which eventually ice-out the world. That
was the first biologically triggered ice age, but others followed, said Richard
Kopp, a Caltech researcher who helped piece together the Snowball Earth
scenario. A new leaf When trees first appeared about
380 million years ago, they also disturbed Earth’s atmospheric
balance. Unlike animals, plants breathe in carbon dioxide and
expel oxygen. Trees transform some of that atmospheric carbon into lignin
(木质素)--the major constituent of wood and one of the most abundant proteins on
the planet. Lignin is resistant to decay, so when a tree dies, much of its
carbon becomes buried instead of released back into the atmosphere as carbon
dioxide. Less carbon dioxide in the atmosphere thins the blanket of gases that
keeps Earth warm, and that cooling effect can trigger global cooling, possibly
even an ice age. "There was some glaciation that started around
that period that was driven at least in part by the evolution of land plants,"
Kopp said in a telephone interview. Trees also affected the
global carbon cycle in another indirect way. As they tunnel through the ground,
tree roots break down silicate rocks into sediment and soil. Silicate rock
contains large amounts of calcium and magnesium (镁). When these elements are
exposed to air, they react with atmospheric carbon dioxide to form calcium
carbonate (碳酸盐) and magnesium carbonate, compounds that are widespread on
Earth. The human difference Though it might seem as if
humans are mere fleas along for a ride on the back of an immense animal called
Earth, our intelligence, technology and sheer numbers mean our species packs a
punch that can shake the world in wild ways. While we are not
the first species to drastically alter our planet, our influence is unique in a
number of ways, scientists say. For one thing, humans have
developed large-scale industry, said Spencer Weart, a science historian at the
American Institute of Physics. "We are capable of mobilizing things beyond our
own biology," Weart said. "I emit a certain amount of carbon dioxide, but my
automobile emits far more." Another is the rate at which humans
are warming Earth. "Humans are the most common large animal to
ever walk the planet," said Kirk Johnson, a chief curator at the Denver Museum
of Nature & Science: "Population, plus brain power and technology, is a
potent combination and the result is that humans are effecting change at very
high rates." Belnap agrees. "I don’t think we’ve fundamentally
changed any process. We’ve just cranked up the speed," she said. "We haven’t
introduced anything new. We’ve just changed how fast or slow it happens, and
mostly fast." But no matter how high humans cause the
temperature to rise and how much damage we do to the planet, Earth and life will
survive, scientists say. It just might no longer be in the form we prefer or the
form that allows us to thrive. "What we need to be thinking of
as humans causing changes to the Earth system is what the consequences will be
to us human beings," said Edwards, the USC geo-microbiologist. "The Earth could
care less. We will be recorded as a minor chaos in the Earth system. The Earth
will go on. The question is: Will we" Even though not the first to influence the earth, the human is still altering the planet in ______.