Abiogenesis and Panspermia

The abiogenesis theory states that life came originated from simple organic compounds that were created on the earth from the pre-biotic soup that existed. However on the other hand, the panspermia theory states that life on Earth originated from comets and asteroids carrying bacterial life from the universe.

The Urey-Miller experiment provides support that the occurrence of abiogenesis is possible. The Urey-Miller experiment aimed to create organic compounds via a system that simulated similar conditions of pre-biotic Earth. The simulation consisted of a recirculating system with heated water (as the ocean), a chamber with electrical charges (as the atmosphere with lightning), and a condenser for gases in the 'atmosphere 'chamber to dissolve in the water. These chambers consisted of ammonia, nitrogen, methane, hydrogen gas, and carbon dioxide. After a while, the experiment's result showed simple organic molecules in the 'atmosphere' chamber, whereas amino acids and other organic acids were found in the 'ocean' chamber.

However, it is still possible for the panspermia to be valid because abiogenesis may have occurred on a different planet and comets may have transported the products to Earth while abiogenesis was occurring on Earth.

Scientists think the RNA replication or metabolism occurred first before protobiont cells began to form in micro environments for many reasons.

Scientists think RNA replication occurred first because RNA have the ability to replicate themselves as well as catalyzing reactions. RNA also have the ability to attract and link amino acids into proteins, which are the building blocks of life. Furthermore, scientists believe that RNA were able to persist because of the clay from volcanic ashes would cover it from harmful UV rays.

Scientists also argue that metabolism occurred before the protobiont cells began to form because they believe that the Earth may have started out with the first living thing on Earth as a primitive metabolic life sustaining itself with a series of reactions with CO2 or CO catalyzed by metal sulfide.

Protobionts are thought to be precursors to prokaryotic cells. They consist of abiotically produced organic molecules surrounded by a membrane like structure. Protobionts have characteristics that are related with life such as simple reproduction, metabolism, excitability, and the maintenance of itself to survive in its environment (with the help of its membrane). Due to this, many scientists believe RNA replication and metabolism occurred before protobiont cells began to form. RNA is needed for the protobiont cells to execute simple reproduction and metabolism is needed so it can energize itself to survive. 

However, whether RNA replication or metabolism may have been the very first occurrences of life, both the abiogenesis and panspermia theories still have validity because organic compounds could have still been created on Earth or survived on a comet traveling to Earth to create protobiont cells.