A Time Line of Earth's Creation

Ga - Giga-annum, Billion Years Ago

5.0 Ga-Gravity Pulls Together a Collection of Gas and Dust

All of the bodies in our solar system have formed from a disk of gas and dusk (mainly composed of hydrogen and helium) that orbited the protosun. Around 5 billion years ago gravity began pulling together some of the gas and dust. This was the beginning of a process that would one day lead to the formation of Earth.

Below: An artist's impression of gravity drawing matter together to form a planet

4.6 Ga-Earth is a Protoplanet

By 4.6 Ga the gravitational vortex had pulled in enough matter to be considered a spherical protoplanet. As a protoplanet Earth was a molten ball of matter with a core of metal. At this time the protoplanet was much less massive than it is today with a mass equivalent to that of the present day planet Venus. Over the next few billion years asteroids, meteors, and other impactors would further augment Earth's mass.

4.5 Ga-Giant Impact

While Earth was still a protoplanet, it was struck by another Mars-sized protoplanet. The impact ejected a lot of matter into space as well as blowing away earth's original atmosphere. It also started Earth spinning on a tilted axis. Gravity pulled the core of the impactor into the mass of the Earth. The remaining debris coalesced into a disk orbiting Earth. Eventually this disk was pulled together by gravity to form the moon we know today.

4.2 Ga-Oceans Begin to Form

As Earth continued to cool, steam was vented through cracks in earth's crust releasing water vapor into the atmosphere. Eventually the water vapor condensed and fell to Earth as rain, but this is accounts for half of Earths water. Over millions of years ice-bearing meteorites collided with the Earth. As the meteorites burned up in the atmosphere their water evaporated. This to eventually condensed into liquid water and fell back to earth. Earth's oceans would become the driving force behind our climate and eventually become the cradle of life.

The Health Effects of UV Radiation

Ultraviolet light is a type of electromagnetic radiation, light, that we receive from the sun. It has a shorter wavelength than visible light, so it is invisible to the naked eye. Its short wavelength also means it is high in energy and dangerous to living organisms. although, UVC, the form of UV light that is highest in energy, is mostly blocked by the atmosphere, UVB is only partially blocked, and UVA isn't blocked at all. Besides sunlight, you can also be exposed to UVA through tanning facilities.

Negative Effects

UV overexposure will result in a long list of health problems. The area most damaged by UV radiation is your skin. Beyond sunburns overexposure can cause wrinkles and premature aging, and if left unchecked ultraviolet radiation will eventually lead to skin cancer. Three types of which, in order of treatability, are basal cell, squamous cell, and malignant melanoma. Besides skin damage UV also damages your immune system and DNA. It also leads to eye damage in the form of blindness, cataracts, and malacular degeneration.

Positive Effects

Despite its many harmful effects, UV actually provides a couple a few health benefits. Ultraviolet light can in small amounts help you produce vitamin D. You only need fifteen minutes of UV a day to produce all the vitamin D you need. You need vitamin D to help your body absorb calcium. The other benefit of UV exposure is it helps your skin produce melanin. Melanin is a dark pigment that goes someway to shielding you from further UV exposure.