Until about 50 years ago, conventional scientific wisdom was that the universe had no beginning. But now there is a broad consensus that the cosmos began with the ‘big bang’ around 13.8 billion years ago.
But even if the universe is not infinitely old, this still raises the question of why it is so old, if it was intended by God as a home for human beings, who themselves have been around for only a tiny fraction of those 13.8 billion years.
But there are good reasons for thinking that in order to produce and support life the universe has to be the age that it is – neither younger nor older.
Firstly, life requires the existent of heavy elements such as carbon, nitrogen, oxygen, phosphorous, potassium, calcium and iron. But these were not present at the time of the big bang, nor for hundreds of millions of years after that. These heavier elements are built up within stars, and it has taken three generations of star formation for these elements to be formed and scattered.
Secondly, such an old universe is required to achieve the present levels (with formation being balanced by decay) of the radioactive elements such as uranium-235, uranium-238 and Thorium-232 that play a critical role in driving plate tectonics and sustaining the earth’s magnetic field. Plate tectonics are necessary for the surface of the earth to be habitable, and the earth’s strong magnetic field deflects deadly cosmic radiation.
Thirdly, sufficient time is required for dangerous events to subside. These dangerous events include frequent supernova eruptions and gamma-ray bursts, and galactic collisions.
Fourthly, the sun – which is about 4.6 billion years old – has now reached an optimally stable phase in terms of solar flaring and luminosity. Advanced life would not have been possible much earlier (or much later).
Fifthly, the early solar system contained a great amount of debris which bombarded the earth on a frequent basis. These bombardments had beneficial effects in terms of seeding the earth with minerals (and possibly water). However, they would rendered the earth inhospitable for several billion years. But, of course, they have now largely subsided.
Sixthly, advanced life on earth requires a rotation rate very close to 24 hours per day. It has taken about 4.5 billion years of interraction between the earth, the Moon and Sun to slow the earth’s rotation rate from 2 or 3 hours per day to the current 24 hours.
Seventhly, adanced life require high levels of free oxygen in the atmosphere. It has taken nearly 4 billion years of photosynthesis to raise the level of oxygen in the atmosphere from 1% to the present 21%.
Eighthly, it has taken the same length of time for the earth’s plate tectonics to produce the continental landmasses that now support abundant life, including human life.
Based on Ross, Why the Universe is the Way it is, Baker, 43-56.