So even though a star might appear extremely dim, if it had a long period it must actually be extremely large. The star appeared dim only because it was extremely far away. By calculating how bright it appeared from Earth and comparing this to its intrinsic brightness, Astronomers could estimate how much of the star's light had been lost while reaching Earth, and how far away the star actually was. In the scale of the Universe, light would take eight minutes to reach the Sun.
And four years to reach Proxima Centauri, the next nearest star. But could light ever cross the entire Universe? Or might it still have a long way to go? Nobody knows for sure. Different elements joining, colliding, breaking apart, and joining again is a very ferocious stage in the life of any planet. Even after the Earth formed, when the atmosphere began to stabilize, it was under siege. Early microbes, in their struggle for life, clashed with and consumed hydrogen gas.
Hundreds of millions of years passed. These microbes evolved into prokaryotes and adapted further, finding energy in sunlight. Then, in a process called photosynthesis, they flooded the atmosphere with oxygen. The rise of oxygen formed a protective layer around the Earth and also helped cool the Earth, eventually encasing the planet with ice in a series of "Snowball Earths" 2.
Some life forms survived, some proliferated, pushing oxygen levels higher. This enabled a greater diversity of life. Combining "bio," meaning life, and "sphere," referencing the Earth's rounded surface, English-Austrian Geologist Eduard Suess coins the term that expressed the portion of the Earth that supports life.
Suess invented the word because he felt it was important to try to understand life as a whole rather than singling out particular organisms.
He believed "biosphere" combines an understanding of the distinct layers that make up the Earth, its atmosphere, and an awareness of all life on our planet and relationships surrounding us.
As knowledge of life on Earth evolves, thinking about it as a biosphere helps explain the entire intertwined network of life. Here's an early look at how the Earth warmed, cooled, and built its biosphere over time.
Not too hot Not too cold Where in our Solar System are the conditions just right to support life? Our planet contains just the right amount of energy and water to support a diverse variety of life. Saturn is too cold and gassy. Life-supporting planets usually posses a heavy-metal core surrounded by a rocky mantle. The surface of Uranus is mostly composed of ices: methane, water, and ammonia. The only energy is lightning, ultraviolet light, and charged particles.
Although it's the kind of environment in which scientists believe life began, it's not viable today. Not only does liquid freeze solid on this dwarf planet, but even gases, like methane, will harden when Pluto is at its most distant, 5. Even as the Universe drifts, the Earth's surface is in continual motion — moving a little more than two centimeters per year, floating on a semi-molten bed of lava.
Along the edges where the continental and oceanic crust plates meet, all sorts of crazy things happen. These massive plates scrape past each other sideways. They dive under each other. And in places, they get snagged, causing tremendous pressures to build. When this tension suddenly releases things happen much, much faster than two centimeters per year. But how do we know that the Earth's surface is moving? Some of the early scholars studying the first world maps began to notice some very odd things — for instance, that West Africa seems to fit nicely into Brazil.
In the early 20th century, a German meteorologist named Alfred Wegener began assembling evidence suggesting that the continents were once connected. He found very similar geological strata in West Africa and in Brazil. And during World War I, he wrote a book arguing that at one time all the continents on Earth had been united in a single supercontinent that he called Pangaea. Journey with our Big Historian team on assignment in Iceland, a land of fire and ice, as they walk upon the spot the North American and Eurasian plates collide.
While other scientists put forth the theory that the Earth's landmasses had once been connected by land bridges that had since sunk into the ocean, and had always been located where they are today, a few renegade scientists postulated that the Earth once contained one huge supercontinent.
In , Austrian geologist Eduard Suess postulated a supercontinent called Gondwanaland, and American astronomer William Henry Pickering suggested in that the continents broke up when the Moon was separated from the Earth. These theories found near-hostile scorn in the scientific community.
So did a theory of a meteorologist named Alfred Wegener. He regarded the Earth as fundamentally dynamic. He believed the great continent, eventually named Pangaea, had broken apart due to continental drifting.
Alfred Wegener was not the first to present continental drifting, but he was the first to put together extensive evidence from several different scientific approaches. Submitting fossil evidence of tropical life on Arctic islands to matching geographical features and formations on separate continents, he argued against transcontinental land bridge claims. He also disputed the theory that mountains formed like wrinkles on the skin of a drying apple, proposing instead that they were created by continents drifting.
They are rich in carbon, either in elemental form or in organic matter, such as aliphatic and aromatic hydrocarbons. Any metals in these asteroids are found as silicates, oxides, or sulfides rather than in the free form.
C-type asteroids that formed beyond the Frost line were able to accumulate ices and hydrated minerals. This information is written for a public audience, including older children: Comets vs. We recommend you start with Solar System Exploration: Asteroids. This page contains information written at an adult level. For information about planetary migration and altering positions of asteroids, check out this press release written by the Southwest Research Institute.
Some asteroids have been compared to enormous rubble piles. For more information on "rubble pile" asteroids, check out Killer Asteroids. Loosely Bound Piles of Trouble. There are a variety of asteroid articles in Planetary Science Research Discoveries ; this educational bulletin is written at a high level for those already familiar with fundamentals of geology:. After the Sun, planets, and moons took form, there were lots of leftovers — balls of ice and rock, plus tiny grains of "dust.
Yet many remained, and are still with us today: a small planet and maybe more than one , icy planetesimals that orbit in the frozen realm beyond the planets, and giant boulders closer to the Sun, including some that cross Earth's orbit, presenting a potential threat to our planet. All of these objects are important to astronomers because they help tell the full story of how the solar system formed and how it evolved.
They also help scientists interpret their observations of other star systems, where big disks of material may be giving birth to planets. Most of these leftovers orbit beyond Neptune, the most distant of the solar system's eight "major" planets.
They formed from the disk of gas and dust that surrounded the newborn Sun. Small particles clumped together to form larger pieces, called planetesimals. These, in turn, merged to form the planets themselves. After the planets were formed, their gravity hurled most of the remaining planetesimals into the Sun or into distant orbits around it. Billions of these icy leftovers orbit in the Kuiper Belt, which is just outside Neptune's orbit, or in the Oort Cloud, which is much more distant.
Asteroids and comets pose a unique problem for life here on Earth. Thousands of these objects orbit the Sun in a kind of celestial pinball game. Their paths take them dangerously close to our home planet. They are known as Earth-crossing asteroids and comets. In addition, it is believed that close encounters with stars may send additional objects from the Oort cloud careening inward towards the planets.
One only has to look at our closest neighbor, the Moon, to see the result of millions of years of cosmic bombardment. Our thick atmosphere protects us from most of the smaller objects, but the big ones sometimes get through. Barringer Crater in Arizona is the result of one such incident. It is nearly a mile across and was formed by a meteor only feet in diameter.
Dozens of other impact craters have also been identified on our planet. They are difficult to find because erosion tends to erase them over time. Many scientists believe that the dinosaurs were killed when a asteroid or comet about 10 miles in diameter plowed into the Earth. This impact left a crater nearly miles in diameter. This impact would have thrown billions of tons of rock and dust into the upper atmosphere, blocking out the sunlight. The result would have been a scenario frequently referred to as nuclear winter.
The cold and lack of sunlight would have killed off all plant life. And without the plants, the animals would have died off. But that was millions of years ago. Could it happen again? Well, something exploded in the atmosphere over Tunguska, Siberia in The explosion knocked down trees like matchsticks in an area covering hundreds of miles. This explosion has been estimated to have been as strong as Hiroshima bombs. The resulting shock wave traveled around the Earth twice.
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