One astrobiologist thinks that the Earth is 3.5 to 4.5 billion years old and the Universe is 12 billion years old. I have noticed that some put a lot of stock into the Earth being 7.5 billion years old with the age of the Universe 20 billion years old. Approximately one billion years ago life existed on the planet Earth. Life forms existed in the shallow epiric seas and then on land as well. Algae not much more complicated than bacteria has been found along with other life forms. By the time the Devonian System existed there were sharks in the seas and plant life similar to vascular plants on land. On the North American Plate broad and shallow riverine-like systems emptied sediment from the areas of the Canadian Shield. Conditions existed so that pontic seas existed across what is now the United States. The majority of life consisted of algae and extremely small worms with "teeth" that look like a tiger's in the pontic/reducing conditions. Rather than go into any detail or any further up the Geologic column, in the space of a few hundred million years river systems had developed and life forms such as sharks existed. There had been major tectonic movement with many marine transgressive and regressive cycles. Even during this short space of time there had been several catastrophic events that had radically affected the whole planet, wiping out almost all life. Life secured places in the sea and on land again each time.
Approximately every 65 million years a major catastrophe occurs affecting the Earth systemically so that there are massive extinctions noticed in the rock record. Of a much shorter periodicity there have been catastrophes that have occurred where the rock record is not affected so that systemic changes are identifiable. However, life has been affected so much so that there have been massive extinctions on part of the planet as well as altered and reduced populations on all of the planet. The periodicity for this is on the order of tens of thousands of years. Intermittent catastrophes have occurred affecting parts of the planet, triggering tectonism and vulcanism on a regional and/or local basis. During times when the Earth was largely unaffected by any outside force a certain amount of stasis provided settings where life went on as it had with normative Earth processes in force.
The point of this is not to teach Geology, Astrophysics, or Biology. The point is to state that there has been change over the past few billion years on Earth caused by normative Earth processes and things from outside the ionosphere. All animal life on Earth that we know of has DNA that at its base is basically the same. There is less than 1% difference between a human and chimpanzee as far as DNA is concerned, yet we are different. We are all composed of the same elements and are carbon-based. Ribose seems to be ribose, whether you might be a cat or a dog. We can group similar animals together because they have similar attributes. So, how did things get so complicated when an exotic species of an animal found near an ocean vent that never gets any sunlight at depth has basically the same "starter" DNA code as I do? Leaving out a lot of detail, just consider one Geologic System versus another. Oxygen levels were different in the atmosphere, levels of radiation were different, all of the available gases had different amounts free in the atmosphere, what elements that were available differed in amount from System to System, the seas and oceanic waters had a different composition determining what microbiotic and macrobiotic life would survive. Gravitation, geomagnetism, and solar radiation were different. While it is true that Earth processes are pretty much the same in a lot of ways producing sedimentation in the same way, details were different such as geochemistry, clay minerology, and attritus in meteoric, riverine, lacustrine, and oceanic water. The amount of land available was different so that highlands and lowlands varied greatly in proportion. After a catastrophic event some animals and plants did not survive into the next System. As the survivors began to flourish in number again, they did so under changed conditions and may have had to migrate. Even in recent history, the amount of free oxygen available to people has changed over the past several thousand years.
Gradualism works as it can and catastrophism works as it will on a very general level. The details of the interplay between life and Earth processes whether a gradualistic model predominates or catastrophism predominates as a determinant vary. An entire race of human beings could be wiped out without people being able to detect that they ever existed from the fossil record. We do know that different races have perished that existed long ago. Out of a few billion years, a few tens of thousands of years is not much time. Occasionally an ephemeral event might be seen in the rock record such as the existence of a paleosol preserved in a part of a Formation next to an abandoned stream channel as if it had been deposited yesterday. We have a lot of evidence to work with but much is forever gone.
In some way, comparing the record we have in the Bible to the Geologic Column is absurd. The Bible tells us that God created everything and leaves it at that. Genesis 1:2 begins with the story of the last Great Destruction and His sovereign act of restoring the planet for this Age of Ages and the smaller ages within it. Sometime before 6,000 years ago much of the life on the planet was wiped out. An Ice Age ended for the same reason that life had been wiped out for many plants and animals. The mechanism was the impact of a near earth object. God said, "Light be," and "Light be." The lights in the sky were visible once again and the Bible tells about this. Something like Carl Sagan's "Nuclear Winter" ended and things got to where the planet was hospitable on a global scale to humans again. The Creation Story begins and ends with Genesis 1:1 and Genesis 1:2 begins to tell the story of Restoration. Seed that had lain dormant began to sprout and life in the seas with roaring waves once again was able to flourish. I am leaving out a great deal of detail that can be had from the Bible too. The animals and plants were blessed, were able to flourish once again, the ones that survived. God finished restoring the planet and rested. In Genesis 2 we find out it had not rained in a long time. Information more specific to humans is given and a part of the story of Restoration not covered before is woven into the Revelation. This part of the story goes back perhaps millions of years to the time that He created Adam and Eve. No one knows how long they lived in the Garden of Eden before being introduced to the purely physical world we live in. There are two stories being told in the surface text at the same time. With some diligence other parts can be gleaned not so obvious. The Bible Codes reveal that more detail is provided in the same verses in addition to what can be found without them.
A question that seems big to people is that about "evolution." Does natural selection as described by Darwin combined with what we now know from such things as genetics, DNA, RNA, and the Human Genome Project explain how things got so complicated? No, it does not. While these things deal with the biology of plants and animals at the most basic level (in the sense of basic research being basic) it does not explain everything. Astrobiologists are not alone in ranging about to fill in some basic information. Our astrobiologist friend sees random chance as ruling all that can be known. He says that is his world view. Do cells replicate the way we think they do? Of course they do. If everything in the Universe (Universes), what we call Creation happens by random chance, then random chance alters how things change over time. However, we know that tectonics are influenced by the activity of the Sun as well as what is going on inside of the Earth and can be explained. A lot of what we do not know scientifically has been attributed to random chance, but is really explicable given enough information and not so random. We thought as recently as the last decade that global warming is due to man's activities and now know that it is not. Even in the face of objective evidence people putter around with conceptual models that no longer apply on this observable phenomenon that is happening now.
Is the Universe that God created probabilistic? Of course. Can it be that God planned everything taking into account probabilities? Of course. Probabilities are something akin to free will that humans have. It is a bit unnerving to realize that God transcends time and "sees" the past or future as easily as we see the present. This gives Calvinists and those opposed to Calvinists a lot to argue about. Catastrophism is something humans deal with in a detached manner or an emotional manner. It introduces the idea of chaos into how we see specific periods of the history of all of Creation and is not favorable to our survival, at least not with the comfort we have grown accustomed to enjoying. Darwin saved the day with a model of how things get on with getting on that favors a totally gradualistic model of the history of the Universe. Things get tough for natural selection if much due is given catastrophism. A lot of scientists said "phew, glad to know catastrophism is meaningless in this Darwin idea, so we can ignore that."
Alverez rekindled the idea of catastrophism with factual evidence in 1981. Scientists would clench their teeth and get angry at the mention of Velikosky as he proposed some heavy-duty catastrophic ideas, that included some unlikely things. The iridium at the Cretaceous and Tertiary boundary along with some other things were reasonable and based on observations though. A big rock did smack into the Earth it turns out. President Jefferson declared that a meteorite did not and could not have fallen on our soil in the early 19th century, but upon investigation finally agreed one had indeed fallen out of the sky. It was popularly thought that rocks did not fall from the sky at the time. Things do not so much evolve over millions of years as they devolve and re-establish. The radiation from a big rock from the sky tends to do strange things to living things if they are not outright killed. I do not think "evolution" explains things by itself, how things got as we see them in comparison and contrast to the rock record. Evolution does not say that it does explain things by itself, but the model is fatally flawed.
If people can ignore enough things that are factual-observable reality, then the Universe is predominated by "random chance" in concert with things we know. However, as rational beings we know that sooner or later things we choose to ignore sooner or later have to be dealt with in some way. I do not think Intelligent Design is far enough along to explain things completely, or apart from changes that take place biologically (evolution) but it does make it possible to not have to do science with one eye closed or half our brains tied behind our backs. The hostility that scientists receive from believers that are not scientists and the hostility that believers receive from scientists that are not believers and all the gradations in between is part of how we learn apparently. People are noticeably unfair with one another within the confines of Theology and Geology apart from one another and any discipline can be substituted such as Biology to replace those first mentioned. Raking one another over the coals tends to separate out those with really silly ideas such as the Flood of Noah explaining the rock record when Theology and Geology meet. The Flood of Noah explaining the rock record is absurd, but ignoring enough facts easily available makes it possible for some to stick to it. Evolution explaining how Adam and Eve got here is as absurd if enough facts are ignored and makes it possible for people to stick to it. Sometimes people are in the pickle Jefferson found himself in, stating rocks do not fall from the sky, when in fact they do.
Does Natural Selection explain anything? Of course it does. Does it explain how we got here? No. We are grouped with primates and some behavior on the part of humans is below that of gorillas for instance. Maybe we were joined at the hip from an evolutionary point of view with other primates at one time. I don't think so and even if it were true, there is no evidence. The statistical probabilities suggesting this is so can be explained without us being cousins that parted ways by means of natural selection. Little people were found to have existed about 15,000 years ago that are very human, just extremely small. That is about 9,000 years before Adam and Eve hit the scene. There are theological questions raised by this and we do not need to make Lucy fully human to challenge the story of Adam and Eve. I am sure that God created Adam and Eve as He said. Notice that God created males and females and He also created Adam and made Eve from the rib of Adam. So, how do we explain that. especially in view of the fact that the name Eve means, "mother of all living?" Getting down to cases, one might want to learn what is meant by "living" as it applies to her. Its not that I have not thought about this, but in short, I will leave it to you to think about. For instance, do you think Cain really went to Nod to find a long lost sister to marry, especially when people there probably included males besides him? Nod was a place where other people lived, a land in the sense of a concentration of people, not the place one of sisters ran off to after the prom.
I have answered essentially without detail, how stuff got complicated in a few billion years in reference to life.
“Look around you, Gabrielle. Lush prairie. And those bushes with orange berries? See them, on those dunes? Sea Buckthorn. It grows wild here, and the oil works wonders on horses.”