2019-11-13 20:05栏目:教育资讯

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The Oak Tree is the king of the Western trees: it has the majestic look with its large canopy top and a straight upward-growing trunk. Oaks are deciduous, meaning their leaves bloom and wither with the whim of seasons. .

Alien life might be purple.


(改1)The oak tree, the average life span of which is about 600 years, is credited to be the undisputed king of the western world which can grow to the height of more than 40 meters.

When spring comes, new leaves and new branches bud from scales on the sturdy old branches, and that announces the onset of the cycle: growing. Growing needs energy. Photosynthesis converts carbon dioxide and sunlight absorbed by chlorophyll in the leaves, into sugar - its own energy source. The sugar is passed down through the phloem in the trunk, to “feed” the whole tree and make all parts grow. Roots grow sideways to form a deep, broad root system, which functions to absorb water and minerals in the soil. The water and minerals then get transported up by the xylem to the leaves, where the photosynthesis process needs water as an essential input.



改1:带头要把oak tree全体的回忆写出来,争取把种种部分的表征都包含在内。

Oak trees self pollinate, or in another word, they produce both female flower and male flowers. The seeds - the acorns, looking like Mr. Potato-head wearing an upside-down scale-skinned bowl, start to develop in those low-profile female flowers nestled among the leaves. Acorns will take one to two years to mature before they fall off the parent tree.

That's the conclusion of a new research paper that suggests that the first life on Earth might have had a lavender hue. In the?International Journal of Astrobiology, microbiologist Shiladitya DasSarma of the University of Maryland School of Medicine and postdoctoral researcher Edward Schwieterman at the University of California, Riverside, argue that before green plants started harnessing the power of the sun for energy, tiny purple organisms figured out a way to do the same.


The oak tree, the king of the western world, has the majesty look with its thick trunk and dense leaves which fall away in winter and then appear in the next spring—a cycle repeating for about 600 years.

In summer, photosynthesis is fueled up by stronger sunlight and more rapid hydraulic cycles in hot temperatures. The tree increases in height, the trunk grows thicker and greener leaves cloud the tree top.



The oak tree has a deep, broad root system to draw water and minerals from the soil, and transmit these nutrients from the root to the rest of the tree. Above the ground, the thick trunk covered with dark, brownish bark grows straight upward, and branches out toward the top, providing shade for travelers and animals in the heat of the day. (改2)​On each branch, leaves are spirally arranged with rounded lobes along the edges. The chlorophyll in leaves plays an important role in undertaking photosynthesis, by which the oak tree can obtain energy from the sunlight and turn water and carbon dioxide into food. (改3)In autumn, the oak tree stops producing this kind of substance, and the leaves then turn orange or bronze, after which they fall away and are replaced by new leaves in the next cycle.

That lush blossom fades as the fall sneaks in: the leaves loses its green since they stop making chlorophyll in autumn, but puts on more red, orange and bronze thanks to the carotenoids and anthocyanins produced in them. Winter will see the whole tree falls asleep with bare branches - waiting for life to revive in the next spring. Oak Trees can live through some 600 such annual cycles.

Alien life could be thriving in the same way, DasSarma said.

Many people tend to think that the Earth is a sphere. In fact, its shape is similar to a sphere, but where the poles are flattened and the equator bulges. This bulge is due to our planet's rotation. This means that the measurement from pole to pole is about 43 km less than the diameter of Earth across the equator.



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On each branch, lobed leaves are spirally arranged where photosynthesis converts carbon dioxides and sunlight absorbed by chlorophyll into food, which is then passed down to the rest of the tree.

"Astronomers have discovered thousands of new extrasolar planets recently and are developing the capacity to see surface biosignatures" in the light reflected from these planets, he told Live Science. There are already ways to detect green life from space, he said, but scientists might need to start looking for purple, too.?





The oak tree stops producing chlorophyll in autumn, so the leaves loses its green but puts on more red, orange and bronze. Winter will see the whole tree falls asleep with bare branches—waiting for life to revive in the next spring.



Oak trees start blooming when they reach the age of 20. The formation of blooms depends on weather conditions and different tree species. Roughly speaking, white oaks bloom in March, two weeks earlier than red oaks, and they are all in full blossom in April. Oak trees bear both male and female flowers, which means they self-pollinate. (改4)The male flowers hanging in clusters produce pollen, while inconspicuous female flowers hidden among twisted branches produce seed—a small oval nut called acorn. The acorn usually contains a hard seed, enclosed in a tough, leathery shell, and borne in a cup-shaped carpel. It usually takes 1 to 2 years for acorns to mature before dropping from the tree, depending on the climate.

The idea that the early Earth was purple is not new, DasSarma and his colleagues advanced the theory in 2007. The thinking goes like this: Plants and photosynthesizing algae use chlorophyll to absorb energy from the sun, but they don't absorb green light. That's odd, because green light is energy-rich. Perhaps, DasSarma and his colleagues reasoned, something else was already using that part of the spectrum when chlorophyll photosynthesizers evolved.

The lowest point on land is relatively accessible. It's the Dead Sea between Jordan, Israel and the West Bank. The surface of this super-salty lake is 1,388 feet below sea level.



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The male flowers hanging in clusters produce pollen, and the seeds—the acorns start to develop in those inconspicuous female flowers hidden among twisted branches. Acorns usually take one to two years to mature before dropping from the tree, which depends on the climate.

That "something else" would be simple organisms that captured solar energy with a molecule called retinal. Retinal pigments absorb green light best. They're not as efficient as chlorophylls in capturing solar energy, but they are simpler, the researchers wrote in their new paper.




Retinal light-harvesting is still widespread today among bacteria and the single-celled organisms called Archaea. These purple organisms have been discovered everywhere from the oceans to the Antarctic Dry Valley to the surfaces of leaves, Schwieterman told Live Science. Retinal pigments are also found in the visual system of more complex animals.

俄勒冈高校的微型生物遗传学家Shil DasSarma感到,前几天地球上的人命是海洋蓝的,但在最早恐怕是浅紫蓝的。他说,南齐的原生生物恐怕应用了叶绿素以外的分子来行使太阳光线,而正是这种分子授予了生物水晶色的色彩。


It used to be purple … well, life on early Earth may have been just as purple as it is green today, suspects Shil DasSarma, a microbial geneticist at the University of Maryland. Ancient microbes, he said, might have used a molecule other than chlorophyll to harness the sun's rays, one that gave the organisms a violet hue, he suggests.

The appearance of the pigments across many living organisms hints that they may have evolved very early on, in ancestors common to many branches of the tree of life, the researchers wrote. There is even some evidence that modern purple-pigmented salt-loving organisms called halophiles might be related to some of the earliest life on Earth, which thrived around methane vents in the ocean, Schwieterman said.

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Regardless of whether the first life on Earth was purple, it's clear that lavender life suits some organisms just fine, Schwieterman and DasSarma argue in their new paper. That means that alien life could be using the same strategy. And if alien life is using retinal pigments to capture energy, astrobiologists will find them only by looking for particular light signatures, they wrote.



Earth's atmosphere is thickest within the first 50 km from the surface or so, but it actually reaches out to about 10,000 km into space. It is made up of five main layers – the Troposphere, the Stratosphere, the Mesosphere, the Thermosphere, and the Exosphere. As a rule, air pressure and density decrease the higher one goes into the atmosphere and the farther one is from the surface.

Chlorophyll, Schwieterman said, absorbs mostly red and blue light. But the spectrum reflected from a plant-covered planet displays what astrobiologists call a "vegetation red edge." This "red edge" is a sudden change in the reflection of light at the near-infrared part of the spectrum, where plants suddenly stop absorbing red wavelengths and start reflecting them away.

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Retinal-based photosynthesizers, on the other hand, have a "green edge," Schwieterman said. They absorb light up to the green portion of the spectrum, and then start reflecting longer wavelengths away.




Astrobiologists have long been intrigued by the possibility of detecting extraterrestrial life by detecting the "red edge," Schwieterman said, but they may need to consider searching for the "green edge," too.

It actually takes 23 hours, 56 minutes and 4 seconds for the Earth to rotate once completely on its axis, which astronomers refer to as a Sidereal Day. But the Earth orbits around the Sun. Every day, the Sun moves compared to the background stars by about 1° – about the size of the Moon in the sky. And so, if you add up that little motion from the Sun that we see because the Earth is orbiting around it, as well as the rotation on its axis, you get a total of 24 hours.This is what is known as a Solar Day, which – contrary to a Sidereal Day – is the amount of time it takes the Sun to return to the same place in the sky.


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"If these organisms were present in sufficient densities on an exoplanet, those reflection properties would be imprinted on that planet's reflected light spectrum," he said.




The southern continent is a place of extremes, with the Antarctic ice cap containing some 70 percent of Earth's fresh water and about 90 percent of its ice, even though it is only the fifth largest continent. Did you know Antarctica is actually considered a desert? Inner regions get just 2 inches (50 millimeters) of precipitation a year (typically as snow, of course).

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Coral reefs support the most species per unit area of any of the planet's ecosystems, rivaling rain forests. And while they are made up of tiny coral polyps, together coral reefs are the largest living structures on Earth — a community of connected organisms — with some visible even from space, according to NOAA.

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