Earth

Earth, our home planet, is a beautiful blue and white ball when seen from space. The third planet from the Sun, it is the largest of the inner planets. Earth is the only planet known to support life and to have liquid water at the surface. Earth has a substantial atmosphere and magnetic field, both of which are critical for sustaining life on Earth. Earth is the innermost planet in the solar system with a natural satellite – our Moon. Explore our beautiful home planet – unique in our solar system - through the links in this section.

Earth's Interior and Surface

Earth, the largest and densest rocky planet, was formed about 4.5 billion years ago. The Earth's interior is divided into four layers, which is typical of rocky planets. Each layer has different characteristics and is made of different elements and minerals.
There are many different types of features on Earth’s surface due to the complexity of our planet. The surface is unique from the other planets because it is the only one which has liquid water in such large quantities. Water forms some features of Earth's surface such as rivers, oceans, beaches and lakes. Other surface features, such as mountains, earthquakes and volcanoes, are formed when large pieces of the Earth’s outer layer move slowly by plate tectonics.

Structure of the Interior of Earth

Earth has a diameter of about 12,756 km (7,972 mi). The Earth's interior consists of rock and metal. It is made up of four main layers:
1) the inner core: a solid metal core made up of nickel and iron (2440 km diameter)
2) the outer core: a liquid molten core of nickel and iron
3) the mantle: dense and mostly solid silicate rock
4) the crust: thin silicate rock material
The temperature in the core is hotter than the Sun's surface. This intense heat from the inner core causes material in the outer core and mantle to move around.
The movement of material deep within the Earth may cause largeplates made of the crust and upper mantle to move slowly over the Earth’s surface. It is also possible that the movements generate the Earth's magnetic field, called the magnetosphere.

This diagram shows the different layers found inside the Earth.
Click on image for full size
Windows Original.

Surface of the Earth

Most of the Earth's surface (70%) is covered with water, and the remaining 30% is taken up by the seven
continental landmasses. However, underneath the water that fills the oceans, and the dirt and plants that cover the continents, the Earth’s surface layer is made of rock. This outer layer formed a hard, rocky crust as lava at the surface cooled4.5 billion years ago.
The crust is broken into many large plates that move slowly relative to each other. Mountain ranges form when two plates collide and their edges are forced up. In addition, many other surface features are the result of themoving plates. The plates move about one inch per year, so millions of years ago the continents and the oceans were in different positions. About 250 million years ago, most of the land was connected together, and over time has separated into seven continents.

Surface Features of the Earth

This image of the surface of the Earth shows the North and South American continents, as well as the floor of the Pacific Ocean. As can be seen in the image, the ocean floor shows evidence of

mid-ocean spreading ridges
individual volcanic island formation.
subduction

The continental regions show evidence of

volcanoes (a portion of the "Pacific Rim of Fire")
non-volcanic mountain ranges
island arcs
faulting.

(Click on the image to see labeled examples of these features.)
These things provide evidence that, unlike other planets, the surface of the Earth is in motion. Motion of the Earth's surface is called plate tectonics.Compare this active surface with that of Venus, Mars, or Europa.

What Is an Earthquake?

The expression “on solid ground” is often used to describe something as stable. Usually the solid ground underfoot seems very stable. But sometimes it is not.
"The ground seemed to twist under us like a top while it jerked this way and that, and up and down and every way," wrote a person describing the experience of being in the large 1906 earthquake in San Francisco, CA.
Earthquakes happen as large blocks of the Earth’s crust move suddenly past one another because of the force of plate tectonics. These blocks of the Earth’scrust meet at cracks called faults. Sometimes those pieces do not slide smoothly past one another. There can be friction along the fault – jagged edges that snag the blocks of rock. This makes it difficult for them to move past each other. Sometimes they get stuck together temporarily. When the pieces of rock overcome the snags, energy is released. The release of energy causes shaking at the ground surface.
The location inside the Earth where an earthquake begins is called the focus. The point at the Earth’s surface directly above the focus is called the epicenter. The strongest shaking happens at the epicenter.
Each year, more than a million earthquakes occur worldwide. Most of these are so small that people do not feel the shaking. But some are large enough that people feel them, and a few of those are so large that they cause significant damage.
Earthquakes can cause damage to things like buildings, bridges, and roads. Earthquakes can cause landslides and mudslides, too. If a large earthquake happens under the ocean it can cause a tsunami – a giant ocean wave or series of waves.
Scientists can figure out whether an earthquake is likely to happen in a place by studying plate tectonics, thefaults underground, and the history of the area’s earthquakes. However, unlike weather events, earthquakes can not be forecast ahead of time.

This diagram shows an earthquake along a fault. The focus of the earthquake is where the energy is released underground. The epicenter is the spot on the Earth’s surface directly above the focus.
USGS and NPS

Volcanoes

There are several ways in which a volcano can form, just as there are several different kinds of volcanoes. Volcanism is part of the process by which a planet cools off.
Hot magma, rising from lower reaches of the Earth, eventually, but not always, erupts onto the surface in the form of lava. During the eruptionof a volcano, flowing lava and ash, forming a large cone. This cone is what we know as a volcano.
Among the different kinds of volcanoes are:

shield volcanoes
cinder cones
composite volcanoes

The most prevelant of kinds of volcanoes on the Earth's surface are the kind which form the "Pacific Rim of Fire". Those are volcanoes which form as a result of subduction of the nearby lithosphere.

This is a volcanic "cone".
Click on image for full size
Courtesy of USGS

An Overview of Earth History

The Earth has been around for approximately four and a half billion years! The geologic time scale is the timeline that describes all this time.
Scientists have found rocks that formed during every time period of Earth's history! In sedimentary rocks, they have found millions of fossils and clues to past environment. Take a look at the stories below to discover how some scientists are discovering more about our planet's past.

Missing Link Between Whales and Four-Footed Ancestors Discovered
Did Life First Form in a Mica Sandwich at the Bottom of an Ancient Sea?
Using Leaves From the Past to Tell the Future!
Digging Woolly Rhinos
Did T-Rex Have a Plant-Eating Relative?
Diamonds are Ancient History
Geologic Findings Undermine Theories of Permian Mass Extinction Timing
Old Rocks Give New Clues about Ancient Earth
Evolution Hits the Beach - streaming RealVideo (1 min. 7 sec.) from NSF
The History of the Universe in 60 Seconds or Less - Dr. Eric Schulman - streaming RealVideo (1 min. 16 sec.) from NSF
The table below provides a brief overview of Earth history. M stands for millions of years. The present time is at the top of the table and ancient time is at the bottom of the table.

Where the continents were	Eras	Approximate age (in years)	Subdivision	Approximate duration (in years)	Notes
Earth, 20 M ago	CENOZOIC	10,000 2 M 5 M 24 M 37 M 57 M 66 M	HOLOCENE PLEISTOCENE PLIOCENE MIOCENE OLIGOCENE EOCENE PALEOCENE	3 M 19 M 13 M 20 M 9 M	The beginning of the Eocene was a period when the Earth was very hot, with palm trees and alligators at the north pole. Earth but cooled by the start of the Quaternary. This period relates to today's concern about global warming. Homo sapiens evolved and Ice Ages occures towards the end of this time. The Little Ice Age(which is not a true ice age) occured a few hundred years ago.
Earth, 190 M ago	MESOZOIC	144 M 208 M 245 M	CRETACEOUS JURASSIC TRIASSIC	78 M 64 M 37 M	The Mesozoic is the period in which the dinosaurs lived, and its end was marked by the K-T extinction. This extinction event dramatically changed the Earth's flora and fauna, and its causes are still being investigated by scientists around the world. During the Mesozoic, the giant continent Pangaea broke apart into the continents we have today.
Earth, 400 M ago	PALEOZOIC	286 M 360 M 408 M 438 M 505 M 570 M	PERMIAN CARBONIFEROUS DEVONIAN SILURIAN ORDOVICIAN CAMBRIAN	41 M 74 M 48 M 30 M 67 M 65 M	The Cambrian period, at the beginning of the Paleozoic, was the first time that multicellular life forms florished on Earth. By the end of the Paleozoic, and beginning of the Mesozoic, all the continents of the Earth came together to form the giant continent called PANGAEA and dinosaurs began to roam on land.
Earth, 540 M ago (end of Precambrian)	PRECAMBRIAN	2800 M 4800 M	PROTEROZOIC ARCHEAN	2300 M 2000 M	This period is about 5 times as long as the Paleozoic and Mesozoic combined, a very long time. Less is known about it than the younger time periods. The oldest fossils are of bacteria/archaea dating from 3000 M. The oldest rock is dated at 3800 M. The Earth is thought to be 4600 M years old.

Scientists Who Study Rocks

Geology is the study of rocks and geologists are the people who study them! There are many different types of geologists. Some of the common types are listed below.

Mineralogists study minerals.
Petrologist study rocks.
Structural geologist study how plate tectonics moves and squishes rocks.
Paleontologists study Earth history and fossils.
Stratigraphers study how layers of sedimentary rock form thoughgeologic time.
Geomorphologists study how the land surface is shaped by water, wind and ice.

What is a geologist like? Well, they are all very different. Click on the links below to get to know some famous geologists.

Florence Bascom, a mineralogist and petrologist, led the way for American women geologists over 100 years ago.
Charles Darwin was the first scientist to publish a comprehensive theory of evolution in the19th century.
Stephen Jay Gould expanded Darwin's theory with his own concept of punctuated equilibrium in the 20th century.
Friedrich Mohs, a mineralogist, developed a way to identify minerals by their hardness.
Leonardo da Vinci did a little bit of everything! When he was not painting the Mona Lisa, he was a scientist and discovered how sedimentary rocks and fossils are formed.

These geologists are exploring granite rocks on a mountain ridge.

Suspended clay particles, eroded from the Cascade Mountains of Washington State, give Lake Diablo its brilliant color. The active volcanoes of the Cascades result from the subduction of the Juan de Fuca plate beneath North America.
Click on image for full size
Courtesy of Nicole LaDue

Earth Science Literacy Framework

Big Ideas of Earth Science

Earth is our home. We rely upon it for our existence in many different ways. Our planet's rocks, soils, and the chemical, physical, and biologicalprocesses that create and transform them, on the continents and beneath the oceans, produce resources and materials that sustain our way of life. Even modest changes to the Earth system, of which these are a part, have had profound influences on human societies and the course of civilization.
It is important to understand the Earth sciences - to be Earth science literate - at this time in history. Many challenges facing humanity, from dwindling energy and mineralresources, to water shortages andchanging global climate, directly relate to the Earth sciences. There are many difficult decisions that governments, local and national, will have to make concerning these issues. We need citizens and governments that are Earth science literate to create policies that appropriately weigh the importance of resource conservation, use, and sustainability.
This Earth system science literacy guide identifies the Big Ideas and fundamental concepts that individuals and communities should understand to make informed decisions. Earth science literacy is very important if we are to understand how the entire Earth system and our climate function. For more information on this effort, please visit the Earth Science Literacy Initiative web site. In addition, the Earth Science Literacy Framework has beenaligned with the National Science Education Standards.

Big Idea 1: Earth scientists use repeatable observations and testable ideas to understand and explain our planet.
Big Idea 2: Earth is 4.6 billion years old.
Big Idea 3: Earth is a complex system of interacting rock, water, air, and life.
Big Idea 4: Earth is continuously changing.
Big Idea 5: Earth is the water planet.
Big Idea 6: Life evolves on a dynamic Earth and continuously modifies Earth.
Big Idea 7: Humans depend on Earth for resources.
Big Idea 8: Natural hazards pose risks to humans.
Big Idea 9: Humans significantly alter the Earth.

Beauty Of The Earth

Sunday, February 6, 2011

All About Earth