Young Earth Creationists believe that God created the world and likely the entire universe in six 24-hour day periods.
Old Earth Creationists believe that God created the world over long periods of time, where each creative day is thousands or millions or billions of years.
Evolutionary Creationists believe that life evolved on earth over billions of years, but that God purposefully directed evolution to produce all life, even humans.
Rom 5:12 Therefore, just as sin entered the world through one man, and death through sin, and in this way death came to all people, because all sinned—
1 Cor 15:20 For the creation was subjected to frustration, not by its own choice, but by the will of the one who subjected it, in hope 21 that[h] the creation itself will be liberated from its bondage to decay and brought into the freedom and glory of the children of God.
I like science, but I'm not a scientist. I think I understand the arguments but I'm ill prepared to provide a convincing scientific argument for a Young Earth Creation to people who do not believe the Bible.
But for Christians, I have some questions:
Did death come upon creation when Adam sinned?
Does the Bible consider death a normal part of life, or a consequence of evil?
Is death, something to be conquered or tolerated?
Something not there in the beginning and not there in the end?
Does the Bible consider death evil or good?
The problem with Old Earth Creation is not in reconciling the Creation account with fossil records or carbon dating but with scripture itself.
Imagine, no death in the world, no sickness, a perfect paradise. Imagine two little bugs, male and female, with all the food they can eat, even if -- without food they might not die? How many bugs will there be in a year? In a thousand years? A million? Imagine thousands (at the least) species of bugs? Imagine thousands of species of other animals. If God created man, perfect, and gave him everything in the garden to eat (before the Fall), then it is clear that eating and consuming are part of the good, natural order.
Simply, if death did not enter the world until the Fall, then you have massive population problems, competition for resources, long before Adam arives on the scene. Adam would be up to his nose in crickets before he took his first breath. The earth, even perfect, is not built to sustain exponential multiplication of every created life form.
Adam and Eve did not have children until after the Fall. If God did not intend for creatures to multiply until after the Fall, then you answer the problem of over-population, but then you don't need thousands or millions of years until Adam. Old Earth is supposed to harmonize with the fossil record showing massive, ancient deaths, but if there's no multiplying before Adam, than you've said the fossil record is wrong anyway.
If the earth is millions or billions of years old, then death is necessary. Competition for scarce resources demands it. And ancient fossils are nothing except dead animals. If we accept their age, but accept that the Bible is correct when it records roughly 6000 since Adam's time, then death reigned before Adam's fall and the Bible is lying. If Adam is older than this, then the Bible is lying.
Did God create a Creation that was already dying and call that good? Where Universally people proclaim that death as evil? Where God sent his only Son to die so we wouldn't have to? People even accuse a good God of being evil because he permits death and suffering. Are we really supposed to teach them that God created death and called it good?
Evolutionary Creation has the same problem, but worse. Evolution theory *depends* on new species developing from old species, but each development is "tested" through survivability. Genetic mutations that sometimes make one creature more competitive for scarce resources usually result in corruptions that instead make other creatures less competitive and they die faster. Evolution depends on death. Death is the significant factor in the evolution story. Natural selection selects one organism to live and multiply and another to die. If God used this process, every animal, then was created by God to die.
Those who are consistent will admit that Adam was then born already dying. Some even suggest that the ancient fossil men or monkey-men, are forefathers to Adam.
In Exodus 16:29, 20:11, 31:17 we learn to honor the Sabbath day of rest because God worked six days, and then rested on the Seventh.
For Christians to abandon the simple language that God created the heavens, earth and all that is in them in six simple days, is to open ourselves up to not trusting scripture, that death is the result of sin alone, that death is unnatural, and that Christ died -- needed to die -- to save us from the unnatural.
If death is natural, then God in Christ is a liar. Christ's death is a gesture but unnecessary to undo death, since God could reverse death without touching sin one way or another.