Regarding Robert Gentry's claims of an instantaneous creation, I think I can agree 100% with his evidence for that. However, perhaps he has yet to answer why said creation should be limited to having occurred six millennia ago. The fact is, once the polonium had made its halos in the rock, there is nothing further to tell us how long ago that event occurred. The rock cannot inform us definitively as to the passage of time since the event of its creation. All the halos do is to substantiate the Bible in that "He commanded and it stood fast." It was an instant creation. But we know not when it occurred.
The Genesis account clearly speaks of the water and the land mass as having pre-existed Creation Week when all life on earth was created and when the earth itself was given form. The land was covered in water up to that time, and by the Word was transformed into dry land which God then named "Earth." But there is no indication in the Biblical record for how long the water and the wet land existed prior to the beginning of that special week in which they were given meaning.
Did God create both the land and the water? Certainly. But they were already there when He chose to develop them further in what would place life in them--the six days of Creation Week.
For this reason, I have no clear argument against the earth being millions of years old. However, any fossils or sedimentary layers containing fossils (cretacious rock) would necessarily be no more than six thousand years old. Where Dr. Gentry is finding his radiohalos, in granite, is rock that we have no way of dating presently, to the best of my knowledge. Dr. Gentry may choose to believe that the evidence points toward the elements themselves being no more than 6000 years old, yet the Bible does not limit us to merely this option. In fact, the implication is there that the elements existed long before Creation Week.
"In the beginning..." seems to place the creation of Heaven and Earth at the same time. There are several ways of interpreting this. Some believe that God's own heavenly home was created at that time and that all stars and planets were created together just six thousand years ago. But that the celestial Heaven pre-existed Creation Week is evident in the story of the rebellion and war there which occurred prior to our Creation Week.
Consider the following statements by Mrs. White.
Thus under a new disguise the great rebel still carries forward his warfare against God, begun in Heaven, and for nearly six thousand years continued upon the earth. {GC88 552.2}
The controversy started in heaven first, and later came to earth.
Before the entrance of evil, there was peace and joy throughout the universe. All was in perfect harmony with the Creator's will. Love for God was supreme, love for one another impartial. Christ the Word, the only begotten of God, was one with the eternal Father,—one in nature, in character, and in purpose,—the only being in all the universe that could enter into all the counsels and purposes of God. ... Before his fall, Lucifer was first of the covering cherubs, holy and undefiled. ... “Thou art the anointed cherub that covereth; and I have set thee so; thou wast upon the holy mountain of God; thou hast walked up and down in the midst of the stones of fire. Thou wast perfect in thy ways from the day that thou wast created, till iniquity was found in thee.” [Ezekiel 28:12-15, 17.] ... All Heaven had rejoiced to reflect the Creator's glory and to show forth his praise. And while God was thus honored, all had been peace and gladness. But a note of discord now marred the celestial harmonies. The service and exaltation of self, contrary to the Creator's plan, awakened forebodings of evil in minds to whom God's glory was supreme. The heavenly councils pleaded with Lucifer. The Son of God presented before him the greatness, the goodness, and the justice of the Creator, and the sacred, unchanging nature of his law. God himself had established the order of Heaven; and in departing from it, Lucifer would dishonor his Maker, and bring ruin upon himself. But the warning, given in infinite love and mercy, only aroused a spirit of resistance. Lucifer allowed jealousy of Christ to prevail, and he became the more determined. ... God, in his great mercy, bore long with Lucifer. He was not immediately degraded from his exalted station when he first indulged the spirit of discontent, nor even when he began to present his false claims before the loyal angels. Long was he retained in Heaven. Again and again he was offered pardon, on condition of repentance and submission. Such efforts as only infinite love and wisdom could devise, were made to convince him of his error. The spirit of discontent had never before been known in Heaven. Lucifer himself did not at first see whither he was drifting; he did not understand the real nature of his feelings. But as his dissatisfaction was proved to be without cause, Lucifer was convinced that he was in the wrong, that the divine claims were just, and that he ought to acknowledge them as such before all Heaven. Had he done this, he might have saved himself and many angels. He had not at this time fully cast off his allegiance to God. Though he had forsaken his position as covering cherub, yet if he had been willing to return to God, acknowledging the Creator's wisdom, and satisfied to fill the place appointed him in God's great plan, he would have been re-instated in his office. But pride forbade him to submit. He persistently defended his own course, maintained that he had no need of repentance, and fully committed himself, in the great controversy, against his Maker.
This passage indicates that the rebellion in Heaven took time. It took time for the seeds of doubt, pride and jealousy to take root in Lucifer's mind. It took time for his rebellion to mature. God bore long with him. If this has any comparison to how long God has borne with us, it may have been much longer than many suppose. But more than any of this, these passages imply an existence in Heaven that predates sin--an existence that may have lasted for ages before sin ever entered. Heaven existed before our Creation Week. How else could we be the "crowning act?" The final, and best of God's creations could only have come after other creations were already made. The universe, therefore, cannot be dated the same as our own period of existence as human beings.
Blessings,
Green Cochoa.