Facts for kids: How old is the Earth?

The Earth

The Earth was a deadly place 4.5 billion years ago.

It’s widely agreed the Earth is approximately 4.54 billion years old. Scientists examined a variety of meteorites, lunar samples, and rocks to answer the age-old question.

While small crystals of zircon from the Jack Hills of Western Australia are at least 4.404 billion years old, meteorites have been dated at 4.567 billion years old. This finding provides both an age for the solar system and guide for determining the age of Earth.

Meteorites are important in this process because Earth essentially formed from the space dust, asteroids and meteors left over after the sun burst into life. As these ‘ingredients’ came together, the gravitational pull of the growing mass of rock caused more material to be attracted to it.

The new Earth was deadly to life as we know it. There was no atmosphere, the surface was boiling with lava, and the planet was surrounded by a cloud of dust.

Short answer: Although some religious followers claim the Earth is only 6000 years old, scientific findings put the age of the planet at 4.54 billion years.

Facts for kids: How many countries are there in the world?

South Sudan

South Sudan is the newest country.

When it comes to knowing how many countries there are in the world, the question is a loaded die. Some countries don’t formally recognise the existence of other countries. Some dependent territories ambitiously regard themselves as countries, and some countries are politely ignored so as to not upset the neighbours.

China regards Taiwan as a breakaway province and Russia doesn’t recognise Kosovo. Argentina claims the Islas Malvinas even though almost nobody on the Falkland Islands wants to live under Argentine rule. It’s all very awkward, especially at social gatherings.

So, to put it simply, the number of countries in the world depends on who you want to believe. Seeing as they have an enormous stockpile of weapons, a habit of picking fights overseas, and are likely recording all my data, it’s in our best interests to get behind the USA’s count of how many countries there are.

The United States Department of State recognises 195 independent states. An independent state is defined as a people politically organized into a sovereign state with a definite territory recognized as independent by the USA. A notable omission to the list of states is Taiwan, which is recognised as being part of China (because China has a lot of power and throws a mighty tantrum whenever anybody asks Taiwan out to dinner). Still, Taiwan is often regarded as an unofficial 196th country when China isn’t listening.

The USA also recognises 66 dependencies and areas of special sovereignty, many of which are a relic of the colonial era when people could just steal what they wanted because they had all the guns and ammunition. In this list you’ll find islands, tax havens, and uninhabitable territory.

Short answer: The USA officially recognises 195 countries. Don’t make the mistake of referring to the 193 members of the United Nations as an answer because independent countries such as the Vatican City and Kosovo are not members.

Facts for kids: How do satellites stay in orbit?

satellite in orbit

GOCE in orbit.

Last weekend a car-sized satellite crashed to Earth, landing in the South Atlantic Ocean. The Gravity field and steady-state Ocean Circulation Explorer – GOCE – descended to Earth after it ran out of fuel, giving rise to the question: how do satellites stay in orbit?

There are two main factors involved. Firstly, we have the gravitational pull of the Earth which is known as centripetal force. Secondly, there is the velocity of the satellite in orbit. Velocity imparts a force on the satellite, known as centrifugal force. If the centripetal force exceeds the centrifugal force of the satellite, then the object will fall to Earth. If the centrifugal force is greater than the centripetal force, then the satellite will drift off into space. If the two forces are equal, the satellite will stay in orbit.

A basic rule of thumb is that the lower the orbit, the greater the speed necessary for the satellite to stay on track.

Just to make things tricky, orbiting satellites experience friction. Space is not a perfect vaccum. Gas and dust exert drag on satellites, slowing it down and decreasing its altitude; which, in turn, increases drag and allows Earth’s gravity to win out over the centrifugal force of the satellite. This explains why some satellites have thrusters to maintain orbit.

Have I confused you? Watch this video.

Short answer: Satellites stay in orbit by maintaining a velocity which prevents the object falling to Earth, as well as flying off into the cosmos.