Science is often like a family jigsaw puzzle saga. Nobody makes any progress for a long time, and then somebody organizes some pieces and fills in a section of the puzzle. After some time, someone else fills in another part of the puzzle, and so on, and on, and on. This was never more true than in origin of life research
For thousands of years, scientists, philosophers, and theologians thought that plants arose naturally from inanimate earth. They thought that scripture and logic supported this viewpoint. Then, Pasteur disproved abiogenesis in 1859 and showed that life can only come from life; however, in the 20th century, scientists began to show that organic compounds form naturally and began to make progress in origin of life research in the quest to prove that life can come from nonlife.
This section is intended for those who do not have a background in biology. It describes the four types of organic compounds in cells: carbohydrates, lipids, nucleic acids, and proteins.
After Miller and Urey's experiments in the 1950s, scientists spent decades trying to discover the chemistry of the origin of organic compounds. Finally, in 2009, the Sutherland laboratory found that a mix of sunlight, hydrogen cyanide, and hydrogen sulfide kick off a process that leads to all of the organic compounds required for life - cyanosulfidic chemistry.
Proteins perform functions in cells. Nucleic acids store information. Ribonucleic acid (RNA) acts as both a protein and an information system. This is why scientists think that RNA was a key component in the early evolution of life. Experiments show that RNA replicates and divides, enabling natural selection and evolution.
I think that one of the amazing things about the universe is that fatty acid vesicles (cellular membranes) formed naturally in the early solar system. The proof is that they are in meteorites. What are the odds that phospholipid bilayers would naturally form fatty acid vesicles, which are the basis of cells, out of all the billions of possible organic chemicals? Scientists think about and investigate how fatty acid vesicles could have formed protocells with internal RNA and other organic compounds.
One of the quests of origin of life researchers is the search for relatively simple proteins that might have converted sunlight into energy in early primitive cells. One archaebacteria at Yellowstone National Park has bacteriorhodopsin proteins in its membrane that pump hydrogen ions into the cell. Adenosine triphosphate ATP proteins are also embedded in their cellular membranes, which are powered by the hydrogen ion gradient between the inside and outside of the cell. This is an energy generation system that is much simpler than photosynthetic systems in algae and plants.
One billion years after the relatively simple photosynthetic systems of archaebacteria, the Great Oxidation Event took place 2.5 billion years ago. Many scientists think that this probable jump in oxidation rate was due to the appearance of cyanobacteria (a.k.a. blue-green algae) and its highly evolved photosynthetic system. In a process called endosymbiosis, a eukaryote cell incorporated a cyanobacterium. This became the energy-producing photosynthetic organelle, the chloroplast, in green algae and plants.
Green algae began to form 2 and 3-dimensional structures in the sea. The first land plants were bryophytes such as moss, which can grow on hard surfaces but must live in a wet environment. Plants then evolved vascular systems, roots, leaves with closing stomata, seeds, and finally flowers.
In the second half of the third age, Moses described the natural generation of plants from inanimate earth (Let the earth sprout), at least this was the interpretation for thousands of years prior to Pasteur's experiments in 1859.
Archaean environment. Credit: Tim Bertelink. Used here per CC BY-SA 4.0