#davidchristian

Big History is divided into different thresholds, they all explain something about how everything came the way it is. Threshold 4 is about the formation of the earth and the solar system.

98% of all matter consists of hydrogen and helium. The other 2% was made in threshold 3, these are all the elements in the periodic table. Because there are many different elements, we can make an almost infinite number of different types of matter. Things which are much more complex can be formed, like planets. And exactly that is what threshold 4 is about.

4.6 billion years ago, our solar system was made. This began with the formation of the sun. The sun is formed like any other star, a collapse of a cloud of matter under pressure of gravity. This collapse was probably triggered by a huge supernova explosion (A huge explosion of a dying star). Because of this supernova, lots of new materials were made. Later these elements were used by the formation of planets. A proplyd is a disk of a cloud of matter which is turning really fast. The universe is full of proplyds. The center of a certain proplyd became very hot, which then made our sun. This is the beginning of a new solar system.

Planets are formed by a process which is called accretion. At first you have really big clouds of chemically rich matter, in this case these are the ingredients (in Big History we use this formula: ingredients + goldilocks conditions = new complexity). These clouds spin around the newly forming star. Also you need Goldilocks conditions which are just right. In this threshold the Goldilocks condition was gravity. When atoms and molecules clump together, this is accretion which can form a whole new planet. 

Our Earth was formed relatively late. The really first rocky planets were made within a billion years of the Big Bang. New planets are always a new form of complexity. This because they contain a much greater diversity of chemical substances. And because of this new complexity, we can even make more complex things, things like animals.

When you look at the characteristics of the earth, you will notice that it’s made of only 10% of Hydrogen and Helium. Comparing this to other planets like Jupiter and Saturn, this is a really small amount. There are three types of  planets: ice giants, silicate planets and gas giants. They all have their own characteristics.

Our moon was probably made when an object the size of Mars, collided with our earth. The stuff coming out was orbiting around the earth. Because of accretion, a new planet was made which was our moon. Through these types of processes, which took about 10 to 20 million years, our solar system was 

 Threshold 3 is about stars and elements. With stars they mean how stars are formed, and how they die. With the elements they mean elements in the periodic table, and how they were formed. Because of stars and supernovae, elements were made. Those elements were used by the formation of planets and also our own earth, which is explained in threshold 4. So actually, all these new elements are the ingredients for planets.

Threshold 5 is about biodiversity, it is about how life started. But when you want to have life, you also need an environment where it can live on. After the earth was formed, which is explained in threshold 4, the earth started developing. There came an atmosphere. From now on animals and plants could live on planet earth, forming a new complexity.