Earth

Earth is the third planet from the Sun and the only astronomical object known to harbor life. According to radiometric dating and other sources of evidence, Earth formed over 4.5 billion years ago. Earth's gravity interacts with other objects in space, especially the Sun and the Moon, Earth's only natural satellite.

Key Points

• Shape of Earth is Geoid.
• Consists of 29.08% of land (148.9 million km²)
• Consists of 70.92% of water (361.1 million km²).
• Oceans hold about 96.5% of all Earth's water.
• Distance from sun is 149.6 million km.
• Mass is 5.972 x 10²⁴ kg.
• it is composed mostly of iron (32.1%), oxygen (30.1%), silicon (15.1%), magnesium (13.9%), sulfur (2.9%), nickel (1.8%), calcium (1.5%), and aluminium (1.4%); with the remaining 1.2% consisting of trace amounts of other elements.
• Average density is 5.5 gm/cc.
• Radius is 6,400 km.
• Rotational time is 23 hours 56 minutes 4 seconds.
• Revolution time is 365 days 5 hours 48 minutes 46 seconds.
• Length of Earth's orbit 960 million km.
• Time taken by the sunlight to reach Earth is 8 minutes 18 seconds.
• Minimum distance from the Sun (Perihelion) is 147.9 million km.
• Maximum distance from the Sun (Aphelion) is 152.19 million km.
• Highest point is Mt. Everest 8,848 m (29,029 ft).
• Deepest ocean point is 11,034 meters (36,201 ft).
• The average depth of ocean is about 3,688 meters (12,100 ft),.

Structure of Earth

1. Crust - Outermost layer and ranges from 5-70 km (3.1 - 43.5 miles) in depth. Made of solid rocks. It is mostly made of the lighter elements, silicon, oxygen, aluminium. Because of this, it is known as sial (silicon = Si; aluminium = Al) or felsic.
2. Mantle - This layer is right below the crust. It is made mostly of oxygen, silicon and the heavier element magnesium. It is known as sima (Si for silicon + ma for magnesium) or mafic.
3. Core - Made of solid iron and nickel, and is about 5000–6000^oC. Consists of 2 parts as outer core and inner core. Outer core is liquid layer below the mantle. Inner core is very hot and center of the earth. Due to high pressure inner core called as knife core.