Planet Earth Help (page 3)

Introduction to Planet Earth

From space, our world looks like a brilliant blue marble. Sometimes called the “blue planet,” the Earth is over 70% water and is unique in our solar system. Clouds, fires, hurricanes, tornadoes, and other natural characters may change the Earth’s face at times, but in our solar system, this world is the only one capable of life as we know it.

Native peoples, completely dependent on Mother Earth for everything in their lives, worshipped the Earth as a nurturing goddess that provided for all their needs. From the soil, came plants and growing things that provided clothing and food. From the rivers and seas, came fish and shellfish for food, trade articles, and tools. From the air, came rain, snow, and wind to grow crops and alter the seasons. The Earth was never stagnant or dull, but always provided for those in her care. Ancient people thought Mother Earth worked together with Father Sun to provide for those who honored her.

Today, astronauts orbit the Earth in spaceships and scientific laboratories, 465 km above the Earth, marvel at the Earth’s beauty, and work toward her care. Former astronaut Alan Bean communicates this beauty by painting from experience and imagination. Astronaut Tom Jones publishes books for young and old of his space experiences. Other NASA astronauts, scientists, engineers, and test pilots have communicated their wonder and appreciation for our fragile world through environmental efforts that address earth science issues. The study of geology includes many areas of global concern.

Geology is the study of the Earth, its origin, development, composition, structure, and history.

But how did it all start? What of the Earth’s earliest beginnings? Many scientists believe the Sun was formed from an enormous rotating cloud of dust and gases pulled by gravity toward an ever denser center of mass. The constant rotation flattened things out and allowed debris (some the size of oranges and others the size of North America) to form planets, the Moon, and comets.

The larger pieces of matter in this debris field had enough gravity to grab up smaller cosmic chunks, glob them together, and allow them to grow larger. When the gathering debris got to be over 350 km across, it was slowly shaped into a sphere by gravity. Figure 1-1 illustrates the steps this formation might have taken.

Fig. 1-1. Gravity shaped space debris into a sphere depending on weight and size.

Other scientists think that everything came about in one gigantic explosion, the Big Bang. Everything was pretty much developed and just simply spiraled out to take the places that we know today. In fact, some astronomers believe that the Universe is expanding. They think all the galaxies are getting further and further apart to almost unimaginable distances. Seems like it would be tough to study something that is moving further away from you all the time!

For the study of Earth Science, though, that is not a problem. The entire planet is a laboratory and provides a lot of great samples.

Size And Shape

The shape of the Earth was guessed at for thousands of years. Most early people thought the land and seas were flat. They were afraid that if they traveled too far in one direction, they would fall off the edge. Explorers who sailed to the limits of known navigation were thought to be crazy and surely on the path to destruction. Since many early ships didn’t return from long voyages (probably sunk by storms), people thought they had either gone too far and simply fallen off, or had encountered terrible sea monsters and were destroyed.

It wasn’t until the respected Greek philosopher, Aristotle (384–322 BC), noticed that the shadow cast by the Earth onto the Moon was curved, that people began to wonder about the flat Earth idea. Remember, Aristotle was widely respected in Greece and had written about many subjects including, logic, physics, meteorology, zoology, theology, and economics, so some people wondered if he might be right about the round Earth too. Aristotle believed the Earth was the center of the solar system.

In the early 1500s, Polish astronomer, Nicholas Copernicus, sometimes called the Father of Modern Astronomy , suggested that the Earth rotated around the Sun. His calculations and experiments all pointed to this fact. Unfortunately, many people believed that the Earth was the center of the Universe. They didn’t like the idea of the Earth being just another rock circling the Sun. It threatened everything they believed in, from the way they raised crops, to their faith in God. Copernicus and others to follow him, however, continued to question and write about the way things worked and the Earth’s place in the cosmos.

It didn’t help early people that the Sun, though very bright, doesn’t look all that big in the sky. To someone standing on the Earth and seeing fields, mountains, ocean, or whatever, as far as the eye can see, it was no wonder most people thought the Earth was the center of everything. They had no idea of the distance.

The Earth is known as one of the inner planets in our solar system. The four terrestrial or Earth-like planets found closest to the Sun are Mercury, Venus, Earth, and Mars. They formed closest to the Sun with higher heat than the farther flung planets. Most of the radiation and other solar gases expelled by the Sun blew off high levels of hydrogen, helium, and other light gases to leave behind rock and heavy metal cores. These “hard” planets, including our Moon, are similar chemically and the best picks for establishing human colonies in the near future.

The outer planets , made up of volatile matter slung way out into space, are huge compared to the inner planets. These include Jupiter, Saturn, Uranus, Neptune, and Pluto (the tiny “oddball” of the outer planets made mostly of ice). The giant outer planets have rocky cores, but are mostly made of nebular gases from the original formation of the Sun.

Just as the planets are held in different orbits by the Sun’s gravity, the well-defined rings of Saturn made up of gases and particles are also held in orbit by gravity.

To remember the placement of the nine planets in our solar system, picture a baseball field. The distances are nowhere near proportional, but if you think of the inner planets (Mercury, Venus, Earth, and Mars) as the “infield” and the outer planets (Jupiter, Saturn, Uranus, Neptune, and Pluto) as the “outfield,” it’s easy to keep them straight. Figure 1-2 shows the Earth’s place in our solar system and gives a rough idea of the different sizes of the planets and the Moon.

Fig. 1-2. The solar system has planets of different sizes and composition.

Compared to the gigantic Sun, which is over 332,000 times the mass of the Earth, the Earth is tiny, a bit like the size of a human as compared to the size of an ant. The Sun is 1,391,000 km in diameter compared to the Earth which is approximately 12,756 km in diameter. That means the diameter of the Sun is over 100 times the diameter of the Earth. To picture the size difference, imagine that the Sun is the size of a basketball. In comparison, the Earth would be about the size of this “o.”

Our planet turns on its axis once a day at a tilt of 23.5° to the plane of the Earth’s orbit around the Sun. The other planets spin on their axes as well and roughly share the same plane of rotation as the Earth. The colossal size of the rotating Sun holds the planets in their particular places by gravity.

The plane of the ecliptic is the angle of incline with which the Earth rotates on its axis around the Sun.

The distance to the Sun is an average of 93 million miles from the Earth. This distance is so huge that it is hard to imagine. It has been said that if you could fly to the Sun in a jet going 966 km/hr, it would take over 300 years to get there and back.