2.0.4 How Life Began: Chemistry - Overview

Version 1.3 March 2013                                               (Previous Version)

Scientists don’t know exactly how life began.  No-one else does either. 

But scientists know a great deal about how it happened and are filling the gaps in our knowledge.

Some people believe life is an incredibly improbable accident.  They say even the simplest living thing, a single cell, is an immensely complex system, with about 10,000 different chemicals, including complex molecules like proteins and DNA that often can’t survive outside a cell.  There are thousands of chemical processes going on inside a cell, and if any one of these is slightly out of kilter, the cell dies.  How could all these molecules form and arrange themselves in the right places so that a cell can begin and survive.  The chances of it happening randomly are miniscule.  It would be like a hurricane blowing through a junk yard, sending all the pieces into the sky, and creating a working Boeing 747 airliner.

We explain that cells evolved over many millions of years, after the Earth formed, and in many small steps, not in a single perfect storm.  Simple molecules probably formed early, such as sugars, phosphates, amino acids, fatty acids, purines and pyrimidines.  Simple pre-biotic chemical processes began where there was some source of energy, such as hot springs, perhaps near cavities in rocks or clay.  Over millions of years these processes built up more complex molecules like proteins (out of amino acids), RNA (out of sugar molecules, purines and pyrimidines), and later DNA (out of RNA).  At some stage they were enclosed in a membrane (of fatty acid molecules).  Many combinations of processes would have developed that didn’t last.  Eventually, at least one combination continued to exist and began to reproduce.  This became the first simple cell.

In the chemical process called photosynthesis, a greenish protein containing chlorophyll uses energy from sunlight to split water into a hydrogen ion and oxygen, and the hydrogen joins to carbon dioxide to make sugar molecules.  Earth’s initial atmosphere contained little oxygen, but it was transformed when the photosynthesis in cyanobacteria created the atmospheric oxygen we humans now breathe. 

In the process called respiration, oxygen molecules combine with sugar molecules to form carbon dioxide and water, passing energy to ATP molecules (made of adenine, a nucleotide base, and three phosphate groups) which makes energy available within animals to fuel other cell processes.

Initial simple cells (like the prokaryotes today) somehow absorbed other cell varieties, which are now organelles within cells (such as mitochondria and chloroplasts) of complex cells called eukaryotes. 

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Science is developing natural explanations how life on Earth began that will only get better with time, validating our core value of life, this natural life.