Earth Archives

September 15, 2010October 16, 2016 by Jerry Coffey

What Is Pangaea?

Continents might be necessary for life, especially complex life. This image shows super-continent Pangaea during the Permian period (300 - 250 million years ago). Credit: NAU Geology/Ron Blakey

So, you are curious about what is Pangaea? It was the supercontinent that existed 250 million years ago during the Paleozoic and Mesozoic eras. During the ensuing millenia, plate tectonics slowly moved each continent to its current position on the planet. Each continent is still slowly moving across the face of our world.

The breaking up and formation of supercontinents appears to have happened several times over Earth’s history with Pangaea being one among many. The next-to-last one, Pannotia, formed about 600 million years ago during the Proterozoic eon. Pannotia included large amounts of land near the poles and only a relatively small strip near the equator connecting the polar masses.

60 million years after its formation Pannotia broke up, giving rise to the continents of Laurentia, Baltica, and Gondwana. Laurentia would eventually become a large portion of North America, the microcontinent of Avalonia(a small portion of Gondwana) would become the northeastern United States, Nova Scotia, and England. All of these came together at the end of the Ordovician.

While this was happening, Gondwana drifted slowly towards the South Pole. These were the early steps in the formation of Pangaea. The next step was the collision of Gondwana with the other land mass. Southern Europe broke free of Gondwana. By late Silurian time, North and South China rifted away from Gondwana and started to head northward across the shrinking Proto-Tethys Ocean.

Movement continued slowly until the land masses drifted until their current positions. The list of oceans and microcontinents is too long to include in this article. We have many articles about this full process here on Universe Today. The evidence for Pangaea lies in the fossil records from the period. It includes the presence of similar and identical species on continents that are now great distances apart.

Additional evidence for Pangaea is found in the geology of adjacent continents, including matching geological trends between the eastern coast of South America and western Africa. The polar ice cap of the Carboniferous Period covered the southern end of Pangaea. Glacial deposits of the same age and structure are found on many separate continents which would have been together in the continent of Pangaea.

We know that the existence of supercontinents has been proven. We know that they have existed at different times in the Earth’s history. Also, we know that the tectonic plates are still moving. Is it possible that there will be another supercontinent someday in the distant future.

We have written many articles about Pangaea for Universe Today. Here’s an article about the Continental Drift Theory, and here’s an article about the continental plates.

If you’d like more info on Pangaea, check out the Pangaea Interactive Map Game. And here’s a link to NASA’s Continents in Collision: Pangaea Ultima.

We’ve also recorded an episode of Astronomy Cast all about Plate Tectonics. Listen here, Episode 142: Plate Tectonics.

Sources:
http://en.wikipedia.org/wiki/Pangaea
http://pubs.usgs.gov/gip/dynamic/historical.html
http://library.thinkquest.org/17701/high/pangaea/

September 14, 2010December 24, 2015 by Fraser Cain

Terminator

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No, this isn’t a movie about robots. The terminator is the line that separates day from night on an object lit by a star. You can see evidence of this terminator when you look at the Moon. When we see the Moon, half in light and half in darkness, we’re seeing the terminator line going right down the middle of the Moon.

From our perspective here on Earth, we see the Sun rise from the East, go through the sky and then set again in the West. But if you could see the Earth from space, you would see half the planet is always illuminated, and half the planet is always in shadow. Since the Earth is rotating, we can watch different parts of the planet illuminated, and other parts darkened. The people on the surface of the planet are experiencing the Sun moving through the sky, but really it’s them who are doing the moving.

The location of the terminator depends on the axial tilt of the object. Since the Earth is tilted by 23.5° away from the Sun’s axis, the position of the terminator changes depending on the season. During summer in the northern horizon, the Earth’s north pole never goes into shadow, so the terminator never crosses the pole. And then in winter in the northern horizon, it never comes out of shadow.

If you could orbit the Earth, just above the equator, you would see the terminator line speeding away at approximately 1,600 km/h (1000 miles per hour). Only the fastest supersonic aircraft can match the terminator’s speed. But as you get closer to the poles, the terminator moves more slowly. Eventually at the poles, you can walk faster than the speed of the terminator.

When you see a terminator from afar, it can tell you a lot about a planet or moon. For example, the Earth’s terminator is fuzzy. This means that our planet has a thick atmosphere that scatters the light from the Sun. The Moon, on the other hand, is airless, so its terminator is a crisp line. When you’re standing on the surface of the Moon, it’s either bright or dark, not the in-between twilight that we experience here on Earth.

We have written many articles about the terminator for Universe Today. Here’s an article about why the Sun rises in the East and sets in the West, and here are some Earthrise photos.

If you’d like more info on Earth, check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.

Reference:
NASA Earth Observatory

September 14, 2010December 24, 2015 by Jerry Coffey

What Is Lithosphere

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Every rocky planet has a lithosphere, but what is lithosphere? It is the rigid outermost shell of a rocky planet. Here on Earth the lithosphere contains the crust and upper mantle. The Earth has two types of lithosphere: oceanic and continental. The lithosphere is broken up into tectonic plates.

Oceanic lithosphere consists mainly of mafic(rich in magnesium and iron) crust and ultramafic(over 90% mafic) mantle and is denser than continental lithosphere. It thickens as it ages and moves away from the mid-ocean ridge. This thickening occurs by conductive cooling, which converts hot asthenosphere into lithospheric mantle. It was less dense than the asthenosphere for tens of millions of years, but after this becomes increasingly denser. The gravitational instability of mature oceanic lithosphere has the effect that when tectonic plates come together, oceanic lithosphere invariably sinks underneath the overriding lithosphere. New oceanic lithosphere is constantly being produced at mid-ocean ridges and is recycled back to the mantle at subduction zones, so oceanic lithosphere is much younger than its continental counterpart. The oldest oceanic lithosphere is about 170 million years old compared to parts of the continental lithosphere which are billions of years old.

The continental lithosphere is also called the continental crust. It is the layer of igneous, sedimentary rock that forms the continents and the continental shelves. This layer consists mostly of granitic rock. Continental crust is also less dense than oceanic crust although it is considerably thicker(25 to 70 km versus 7-10 km). About 40% of the Earth’s surface is now covered by continental crust, but continental crust makes up about 70% of the volume of Earth’s crust. Most scientists believe that there was no continental crust originally on the Earth, but the continental crust ultimately derived from the fractional differentiation of oceanic crust over the eons. This process was primarily a result of volcanism and subduction.

We may not walk directly the lithosphere, but it shapes every topographical feature the we see. The movement of the tectonic plates has presented many different shapes for our planet over the eons and will continue to change our geography until our planet ceases to exist.

We have written many articles about the lithosphere for Universe Today. Here’s an article about the lithosphere, and here’s an article about the tectonic plates.

If you’d like more info on the Earth’s lithosphere, check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.

September 2, 2010December 24, 2015 by Jerry Coffey

What Is A Continent

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You know that there are 7 continents(6 if you were taught geography in Europe) right now, but do you really know the definition of what is a continent? There are many different, and confusing definitions of what a continent is. The most widely accepted one says that a continent is defined as a large, continuous, discrete mass of land, ideally separated by an expanse of water. This definition somewhat confuses things. Many of the current continents are not discrete landmasses separated by water. The word large leads to arbitrary classification: Greenland, with a surface area of 2,166,086 km² is considered the world’s largest island, but Australia with a land mass of 7,617,930 km² is a continent. The qualification that each be a continuous landmass is disregarded because of the inclusion of the continental shelf and oceanic islands and is contradicted by classifying North and South America and Asia and Africa as continents, without a natural separation by water. This idea continues if the land mass of Europe and Asia is considered as two continents. Also, the Earth’s major landmasses are surrounded by one, continuous World ocean that has been divided into a number of principal ‘oceans’ by the land masses themselves and various other geographic criteria.

The number of continents has changed throughout the evolution of the Earth. Plate tectonics and continental drift have forced changes on continental composition. The planet began with one single land mass(the Mesezoic Era). This continent was not suddenly there. It was the result of partially solidified magma being smashed together by plate tectonics and continental drift. Those forces remain at work today.

To further confuse things, different parts of the world teach different versions of the continents. The seven-continent model is usually taught in China and most English speaking countries. A six continent model combining Europe and Asia is preferred by the geographic community, the former parts of the USSR, and Japan. Another six continent model combining North and South America is taught in Latin America and most of Europe.
The answer to ‘what is a continent’ is more by convention than strict definition. Hopefully, this will help to clear some of the confusion that you had before you started reading this article.

We have written many articles about the continents for Universe Today. Here’s an article about the biggest continent, and here’s an article about the continental drift theory.

If you’d like more info on Earth’s continents, check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.

Source: Wikipedia

August 19, 2010December 24, 2015 by Nancy Atkinson

MESSENGER Looks Back at the Earth and Moon

Earth and Moon from 114 Million Miles.Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

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A new image to add to the family photo album! The MESSENGER spacecraft is working its way to enter orbit around Mercury in March of 2011, and while wending its way, took this image of the Earth and Moon, visible in the lower left. When the image was taken in May 2010, MESSENGER was 183 million kilometers (114 million miles) away from Earth. For context, the average separation between the Earth and the Sun is about 150 million kilometers (93 million miles). It’s a thought provoking image (every one of us is in that image!), just like other Earth-Moon photos — Fraser put together a gallery of Earth-Moon images from other worlds, and this one will have to be added. But this image was taken not just for the aesthetics.

This image was taken as part of MESSENGER’s campaign to search for vulcanoids, small rocky objects hypothesized to exist in orbits between Mercury and the Sun. Though no vulcanoids have yet been detected, the MESSENGER spacecraft is in a unique position to look for smaller and fainter vulcanoids than has ever before been possible. MESSENGER’s vulcanoid searches occur near perihelion passages, when the spacecraft’s orbit brings it closest to the Sun. August 17, 2010 was another such perihelion, so if MESSENGER was successful in finding any tiny asteroids lurking close to the Sun, we may hear about it soon.

Source: MESSENGER

June 16, 2010January 12, 2016 by Fraser Cain

How Many Miles Around the Earth?

Planet Earth, as seen from Apollo 17 mission. Credit: NASA/)PL

Planet Earth, which we humans and all currently-known forms of life call home, is the third planet from the Sun, and the largest of the terrestrial planets. With a mean radius of 6,371 km (3,958.8 miles), it is slightly larger than Venus (which has a radius of approx. 6,050 km), almost twice the size of Mars (~3,390 km), and almost three times the size of Mercury (~2,440 km).

Basically, Earth is a pretty big world. But just how big if one were to measure it from end to end? If one were to just start walking, how many kilometers (and/or miles) would they have to go before they got back to where they started. Well, the short answer is just over 40,075 km (or just over 24,901 miles). But as always, things get a little more complicated when you look closer.

Continue reading “How Many Miles Around the Earth?”

June 8, 2010December 24, 2015 by Nancy Atkinson

The Earth and Moon May Have Formed Later Than Previously Thought

The collision between "Proto-Earth" and Theia, from which the Earth and Moon were created 4,500-4,400 million years ago. Both planets had a massive iron core when they collided and created the Moon and Earth.

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The Earth and Moon were created as the result of a giant collision between two planets the size of Mars and Venus. Until now it was thought to have happened when the solar system was 30 million years old or approximately 4.5 billion years ago. But new research shows that the Earth and Moon may have formed much later – perhaps up to 150 million years after the formation of the solar system.

“We have determined the ages of the Earth and the Moon using tungsten isotopes, which can reveal whether the iron cores and their stone surfaces have been mixed together during the collision,” said Tais W. Dahl, from the Niels Bohr Institute at the University of Copenhagen in collaboration with professor David J. Stevenson from the California Institute of Technology (Caltech).

The planets in the solar system were created by collisions between planetary embryos orbiting the newborn sun. In the collisions the small planets congealed together and formed larger and larger planets. When the gigantic collision occurred that ultimately formed the Earth and Moon, it happened at a time when both planetary bodies had a core of metal (iron) and a surrounding mantle of silicates (rock). But when did it happen and how did it happen? The collision took place in less than 24 hours and the temperature of the Earth was so high (7000º C), that both rock and metal must have melted in the turbulent collision. But were the stone mass and iron mass also mixed together?

The age of the Earth and Moon can be dated by examining the presence of certain elements in the Earth’s mantle. Hafnium-182 is a radioactive substance, which decays and is converted into the isotope tungsten-182. The two elements have markedly different chemical properties and while the tungsten isotopes prefer to bond with metal, hafnium prefers to bond to silicates, i.e. rock.

It takes 50-60 million years for all hafnium to decay and be converted into tungsten, and during the Moon forming collision nearly all the metal sank into the Earth’s core. But did all the tungsten go into the core?

“We have studied to what degree metal and rock mix together during the planet forming collisions. Using dynamic model calculations of the turbulent mixing of the liquid rock and iron masses we have found that tungsten isotopes from the Earth’s early formation remain in the rocky mantle,” said Tahl.

The new studies imply that the moon forming collision occurred after all of the hafnium had decayed completely into tungsten.

“Our results show that metal core and rock are unable to emulsify in these collisions between planets that are greater than 10 kilometers in diameter and therefore that most of the Earth’s iron core (80-99 %) did not remove tungsten from the rocky material in the mantle during formation” said Dahl.

The result of the research means that collision that created the Earth and the Moon may have occurred as much as 150 million years after the formation of the solar system, much later than the 30 million years that was previously thought.

The research results have been published in the scientific journal, Earth and Planetary Science Letters.

From a University of Copenhagen press release.

June 3, 2010December 24, 2015 by Nancy Atkinson

Early Faint Sun Paradox Explained?

Titan's thick haze. Image: NASA/JPL/Space Science Institute.

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Models of the Sun’s evolution indicate it was as much as 30 percent less luminous during Earth’s early history than it is now. But, somehow the surface of the planet was warm enough for primordial life to emerge. A new study and a look at Saturn’s moon Titan has provided clues for how the Sun could have kept the early Earth warm enough. Scientists say a thick organic haze that enshrouded early Earth several billion years ago may have been similar to the haze that covers Titan and would have protected emerging life on the planet from the damaging effects of ultraviolet radiation, while warming the planet, as well.

Eric Wolf from the University of Colorado-Boulder and his team believe the organic haze was made up primarily of methane and nitrogen chemical byproducts created by reactions with light. If the particles clumped together in larger, complex structures, an arrangement known as a fractal size distribution, then the smallest particles would interact with the shortwave radiation, while the larger structures made out of the smaller particles would affect longer wavelengths. Not only would the haze have shielded early Earth from UV light, it would have allowed gases like ammonia to build up, causing greenhouse warming and perhaps helped to prevent the planet from freezing over.

Other researchers including Carl Sagan have proposed possible solutions to this “Early Faint Sun” paradox, which generally involved atmospheres with powerful greenhouse gases that could have helped insulate the Earth. But while those gases would have blocked the radiation, it wouldn’t have warmed Earth enough for life to form.

“Since climate models show early Earth could not have been warmed by atmospheric carbon dioxide alone because of its low levels, other greenhouse gases must have been involved,” said Wolf. “We think the most logical explanation is methane, which may have been pumped into the atmosphere by early life that was metabolizing it.”

Lab simulations helped researchers conclude that the Earth haze likely was made up of irregular “chains” of aggregate particles with greater geometrical sizes, similar to the shape of aerosols believed to populate Titan’s thick atmosphere. The arrival of the Cassini spacecraft at Saturn in 2004 has allowed scientists to study Titan, the only moon in the solar system with both a dense atmosphere and liquid on its surface.

During the Archean period there was no ozone layer in Earth’s atmosphere to protect life on the planet, said Wolf. “The UV shielding methane haze over early Earth we are suggesting not only would have protected Earth’s surface, it would have protected the atmospheric gases below it — including the powerful greenhouse gas, ammonia — that would have played a significant role in keeping the early Earth warm.”

The researchers estimated there were roughly 100 million tons of haze produced annually in the atmosphere of early Earth during this period. “If this was the case, an early Earth atmosphere literally would have been dripping organic material into the oceans, providing manna from heaven for the earliest life to sustain itself,” said team member Brian Toon, also from CU-Boulder.

“Methane is the key to make this climate model run, so one of our goals now is to pin down where and how it originated,” said Toon. If Earth’s earliest organisms didn’t produce the methane, it may have been generated by the release of gasses during volcanic eruptions either before or after life first arose — a hypothesis that will requires further study.

This new study will likely re-ignite interest in a controversial experiment by scientists Stanley Miller and Harold Urey in the 1950s in which methane, ammonia, nitrogen and water were combined in a test tube. After Miller and Urey ran an electrical current through the mixture to simulate the effects of lightning or powerful UV radiation, the result was the creation of a small pool of amino acids — the building blocks of life.

“We still have a lot of research to do in order to refine our new view of early Earth,” said Wolf. “But we think this paper solves a number of problems associated with the haze that existed over early Earth and likely played a role in triggering or at least supporting the earliest life on the planet.”

Sources: CU-Boulder, Science

May 28, 2010September 23, 2016 by Matt Williams

How Many Earths Can Fit in Jupiter?

Jupiter compared to Earth. Image credit: NASA

Jupiter is known as the “King of the Planets”, and for good reason. For one, it is the largest planet in the Solar System, and is actually more massive than all the other planets combined. Fittingly, it is named after the king of the Roman pantheon, the latinized version of Zeus (the king of the Olympian gods).

Compare that to Earth, which is the largest of the terrestrial planets, but a tiny marble when compared to the Jovian giant. Because their disparity in size, people often wonder many times over Earth could be squeezed in Jupiter’s massive frame. As it turns out, you could it do many, many times over!

Size and Mass Comparison:

To break the whole size discrepancy down, Jupiter has a mean radius of 69,911 ± 6 km (60217.7 ± 3.7 mi). As already noted, this is roughly 2.5 times the mass of all the planets in the Solar System combined. Compared this to Earth’s mean radius of 6,371.0 km (3,958.8 mi), and you could say that Earth fits into Jupiter almost 11 times over (10.97 to be exact).

*Rough visual comparison of Jupiter, Earth, and the Great Red Spot. Approximate scale is 44 km/px. Credit: NASA/Brian0918/ Wikipedia Commons*

And as already noted, Jupiter is more massive than all the other planets in our Solar System – 2.5 times as massive, that is. In fact, Jupiter weighs in at a hefty 1.8986 × 10²⁷ kg (~4.1857 x 10²⁷ lbs), or 1898.6 billion trillion metric tons (2.092 billion trillion US tons).

Compare that to Earth, which has a mass of 5.97 × 10²⁴ kg (13.1668 × 10²⁴ lb) – 5.97 billion trillion metric tons, or 6.5834 billion trillion US tons. Doing the math, we then come to the conclusion that Jupiter is approximately 317.8 times as massive as Earth.

Volume Comparison:

However, figuring for radius is only useful is you are planning on stacking the Earths end to end across the middle of the gas giant. And comparing their masses doesn’t give you a sense of size, seeing as how the planets are widely different in terms of their density.

*Jupiter/Earth comparison. Credit: NASA/SDO/Goddard/Tdadamemd*

To know how many Earth’s could truly fit inside in three-dimensions, you have to consider total volume, which you can calculate using the simple formula of 4/3 x Pi x radius².

Doing the math, we find that Jupiter has a volume of 1.43 x 10¹⁵ km³ (1,430 trillion cubic km; 343 trillion cubic mi) while Earth has a volume of 1.08 trillion km³(259 million mi). Divide the one by the other, and you get a value of 1299, meaning you could fit almost 1300 Earth’s inside Jupiter.

In short, the king of the planets is much, much, MUCH bigger than the planet we call home. Someday, if we ever hope to live around Jupiter (i.e. colonize its moons), we will be able to appreciate just how big it is up close. Until then, these impressive figures will have to suffice!

We’ve written many articles about Jupiter for Universe Today. Here’s Ten Interesting Facts About Jupiter, Jupiter Compared to Earth, What is the Diameter of Jupiter?, and How Much Bigger is Jupiter than Earth?

If you’d like more information on Jupiter, check out Hubblesite’s News Releases about Jupiter, and here’s a link to NASA’s Solar System Exploration Guide to Jupiter.

We’ve also recorded an episode of Astronomy Cast just about Jupiter. Listen here, Episode 56: Jupiter.

Sources:

May 28, 2010December 24, 2015 by Fraser Cain

How Many Earths Can Fit in the Sun?

Earth Compared to the Sun. Image credit: NASA

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So, how many Earths can fit in the Sun? The answer is that it would take 1.3 million Earths to fill up the Sun. That’s a lot of Earths.

The Sun makes up 99.86% of the mass of the Solar System. And it’s the giant planets like Jupiter and Saturn which make the most of that remaining .14% of the Solar System.

If you’d like to do the calculation yourself, here are your numbers. The volume of the Sun is 1.412 x 10¹⁸ km³. And the volume of the Earth is 1.083 x 10¹² km³. So if you divide the volume of the Sun by the volume of the Earth, you get 1,300,000.

Of course, the Sun is a fairly average sized stars. There are some enormous stars out there. For example, the red giant Betelgeuse has a radius of 936 times the radius of the Sun. That gives it hundreds of millions of times more volume than the Sun.

And the largest known star is VY Canis Majoris, thought to be between 1800 and 2100 times the radius of the Sun.

We’ve written many articles about size comparisons for Universe Today. Here’s an article about the Moon compared to Earth, and here’s an article about Saturn compared to Earth.

If you’d like more info on the Sun, check out NASA’s Solar System Exploration Guide on the Sun, and here’s a link to the SOHO mission homepage, which has the latest images from the Sun.

We’ve also recorded several episodes of Astronomy Cast about the Sun. Listen here, Episode 30: The Sun, Spots and All.