“Just 6 million years ago, a single female ape had two daughters. One became the ancestor of all chimpanzees, the other is our own grandmother.” This is a quote from the book Sapiens – A Brief History of Humankind by Yuval Noah Harar. But human life is not the only kind of life existing on this planet. There’s a whole other part of this world, which is infinitely larger than the 7.5 billion of us. This article is about the origin of life and its evolution.
The Big Bang happened, 13.8 billion years ago, fast forward to 4.5 billion years ago, Earth was formed by accretion from the solar nebula. Solar nebula is basically the solar system as a cloud of dust and gas. There are several theories about the history of the earth, the origin of life and evolution, and everything in between. My favorite and the simplest is the one that accredits all of it to God. God made everything. However, the lack of evidence thereof forces me to state theory with scientific backing.
When the Earth was formed, it was not ready for life immediately. The temperature was boiling, the atmosphere was absent and no oxygen to breathe. The Earth became so hot to the point that the iron present on the surface and beneath, melted. It became mobile and got collected to form the core. Further events led to the formation of layers of the Earth that we call mantle and crust.
As the Earth cooled, an atmosphere was formed. It was a result of gases spewing from volcanoes which included hydrogen sulfide, methane, and ten to 200 times as much carbon dioxide as today’s atmosphere. It was only after half a billion years later that the Earth’s surface cooled and solidified enough for water to collect on it. Much of the carbon dioxide dissolved into the oceans.
Gradually, the primary form of bacteria developed that could live on energy from the sun and carbon dioxide in the water and produced oxygen as a waste product. Thus, oxygen levels began to rise in the atmosphere, while the amount of carbon dioxide continued to drop. The origin of life on earth is owed to that bacteria, one could have never imagined.
Protobionts are known to be the precursor to early life and resemble very simple cells. They are microspheres composed of inorganic and organic molecules trapped inside of a lipid bilayer membrane. Similar to cell membranes, the membranes can be selectively permeable and undergo osmotic swelling and shrinking. Protobionts are capable of going through simple reproduction by giving birth to smaller liposome microspheres.
Scientists speculate that RNA was the first genetic material to develop. It is because, unlike DNA, RNA is able to replicate itself. Ribozymes, RNA molecules folded into a particular structure are able to facilitate the replication of other short RNA molecules. The RNA molecules that replicated most effectively would produce the most copies, and just like in natural selection, this would cause RNA to evolve over generations of the self-replicating molecules.
Since these cells originated in a sea of organic molecules, they could obtain food and energy directly from their environment. But such kind of a situation is self-limiting, therefore cells needed to evolve their own mechanisms for generating energy and synthesizing the molecules necessary for their replication. The development of these metabolic pathways led to the alteration of Earth’s atmosphere, thereby changing the course of further evolution.
Cells are divided into two primary classes that were initially defined by the absence or presence of the nucleus. Prokaryotic cells lack a nuclear envelope, whereas eukaryotic cells have a nucleus in which the genetic material is separated from the cytoplasm. Prokaryotic cells are the simpler ones out of the two, given the absence of a nucleus. In spite of these differences, the same basic molecular mechanisms govern the lives of both prokaryotes and eukaryotes which indicates that all present-day cells are descended from a single primordial ancestor.
Jawed vertebrates like fish, birds, and humans make up about 99 percent of the vertebrates on this planet. However, scientists don’t agree on how and when jaws first evolved. Scientists think that the common ancestor of jawed vertebrates was similar to eyeless, boneless, jawless fishes such as hagfish and lampreys. They diverged from their immediate ancestors about 360 million years ago and haven’t changed much since.
Most life forms have evolved initially in marine habitats. Oceans provide about 90 percent of the living space on the planet by volume. The earliest vertebrates appeared in the form of fish, that lived exclusively in water. Some of these evolved into amphibians who spend their lives on land and water partially. Some of the other fish evolved into land mammals and subsequently returned to the ocean. We know them as seals, dolphins, or whales.
As life gradually moved to land, they had to develop a new way to walk. Their skeletons were to support the entire weight because the water supports mass in a way that air simply doesn’t. Ribs changed shape, skulls disconnected, necks evolved, bones were lost and shifted. Overall, it took a long 30 million years or so to develop a body plan fit for walking on land.
Origin of life and evolution is inevitable. It’s a law of the world. It has brought us where we are today and will take us places unimaginable.