1. Origin of the Universe

2. the Big Bang
The universe came into existence suddenly. The common scientific theory is that the universe existed in a concentrated single point, containing all known matter and energy. Approximately 13.7 billion years ago, this single point began to expand – an event that has become known as the Big Bang.

3. It took about 1 million years for the matter in the universe to cool enough for the first elements to form.
Most of the new matter was hydrogen and helium – two very simple elements.

4. a protostar
Theory says that matter accumulations became denser as gravity pulled them together. As the density increased, the matter collapsed and compacted under its own weight, causing a warm, dense core called a protostar.

5. How do scientists theorize that the first stars formed?
Given enough mass, protostars continue to contract, becoming denser until the core pressure and density were so high that nuclear reactions began. The nuclear fusion reaction from protostars creates the stars.
Nuclear fusion is a reaction in which light atoms unite to form heavy atoms, releasing tremendous energy in the process.

6. Nuclear fusion and the theorized “life cycle” of stars provide an explanation of how heavy elements formed in a universe filled predominantly with helium and hydrogen.
Once nuclear fusion begins, a star burns for millions of years, consuming the hydrogen within it.
Astronomers theorize that heavy elements form as hydrogen bonds fuse.

7. the hydrogen becomes exhausted, the star’s core becomes denser
the hydrogen becomes exhausted, the star’s core becomes denser. It eventually collapses under the extreme gravity forces generated by the density. This may cause a large nuclear explosion called a supernova.
The explosion generates heavier atoms. The fusion core collapses and in the supernova, massive stars account for the origin and distribution of heavy elements throughout the universe.

8. Origin of the Solar System
Formation
The current theory among many scientists is that the solar system’s current form, with planets orbiting the sun, began with a large cloud of hydrogen and helium called a nebula.
a. The shock wave of the supernova caused the cloud to condense, which caused it to spin. As the cloud collapsed and became denser, it flattened into a disk due to rotation. At the center a protostar developed which when dense enough began nuclear fusion and became the sun.

9. Some of the gas continued to revolve around the sun, eventually condensing into masses too small to become stars. This is what formed the planets.
The nebular theory is the theory that the solar system originated as a nebula.

10. Origin of the Earth and Moon
According to the nebular theory, Earth and the other planets formed through accretion.
Accretion is the process by which small particles clump together because of gravity. As a mass grows due to accretion, the more gravity it has, and the more additional mass it attracts.

11. Although the Earth didn’t gain enough mass to form a protostar or star, its growing mass caused its core to compress. The core heated and became molten liquid.
The outer core is still molten
Within the molten liquid, heavy matter, such as iron and nickel, sank toward the center, while light matter, such as oxygen and silicon, moved towards the surface.
The process of density stratification formed the layers of the Earth.

12. Formation of the moon
The most widely accepted explanation for the moon’s origin is the Orpheus theory.
A planet-sized body – possibly another planet about one-third the size of Earth – struck Earth during its early development and sent some of its material into orbit, forming the moon.

13. Origin of Atmosphere and Oceans
Early Earth had no atmosphere
Earth was mostly molten liquid and gases did not escape.
Eventually it cooled enough for the surface to solidify into a crust.
After the crust solidified, gases were released by volcanic activity. These gasses accumulated as an early atmosphere of primarily water vapor, carbon dioxide, and nitrogen.
No water could be found do to the high heat
Rain would boil as soon as it hit the ground

14. The Oceans
After further cooling, Earth’s surface allowed rain to accumulate and the oceans formed as water vapor condensed.
Some scientists speculate that additional water may have entered Earth’s atmosphere via comets and other ‘outside’ sources.

15. Scientists believe that the development of oceans began the process that allowed life to form
Carbon dioxide dissolved into the young oceans, leaving a nitrogen-rich atmosphere.
Many scientists think that these were the conditions required for life.
There was no oxygen in the atmosphere on early Earth.
Although oxygen is essential to almost all life today, according to data recorded in rock, early life didn’t use oxygen.
Oxygen entered the atmosphere about 1.5 billion years ago when photosynthesizing organisms began using carbon dioxide and releasing oxygen.