Twice, the explorers run across veins of free metallic magnesium in the ground. Magnesium is extremely active chemically, and is only found in compounds. Since it also has a relatively low ignition temperature, and can burn under conditions that do not normally support combustion (such as under water or in certain oxygen-free environments), it would be unlikely to exist in a place that had been formed out of molten lava.
Sean mentions "booking a flight to Reykjavik". International flights going to, from or through Iceland use Keflavik Airport. The airport in Reykjavik is what most countries would consider a regional airport, unable to handle large jetliners.
Trevor identifies the luminous birds as a species that went extinct "...150 million years ago." However, the oldest known bird, Archaeopteryx, emerged between 150-145 million years ago, meaning that the luminous birds went extinct before birds began.
In the opening, Trevor is explaining continental drift to a class while he plays a video. However, the video shows India moving westward across the Indian Ocean and colliding with Africa. This video is playing in reverse.
When Sean is lying on the "beach" after being carried across the ocean by the kite, he is wearing gloves. In the next shot, when he is standing up, the gloves are gone. In the next shot, he takes the gloves off. In the following shot, as he begins to follow the bird, they are gone again.
(at around 1h 18 mins) In the scene where Prof Anderson, Hannah and Sean are stuck in the magma pipe in the T-Rex jaw, Prof Anderson tries to ignite the magnesium with a flare. He instructs Hannah and Sean to hold his legs so he can reach further down the magma pipe. As he holds the flare to the rock face you can see that the T-Rex teeth are at chest height, indicating that he is not leaning far out of the jaw. When he tries to get back into the jaw you can see the teeth are at waist height now.
Backpacks tend to reappear at certain important plot turns and such. For example; when they first discover the world at the center of the earth, they throw away their backpacks and continue on without them, then, however, they reappear again prior to leaving on the raft and then while on the raft they are gone once more only to reappear once again prior to meeting the dinosaur. As for Sean's backpack, it is clearly missing when he is jumping the floating rocks and then at the end it reappears when they have landed the dinosaurs skull in Italy. Furthermore, no one is seen carrying an extra backpack at any time, maybe suggesting that the other two carry Sean's pack.
When Trevor Anderson looks at the book in his flat, the front cover reads Journey to the Center of the Earth. Moments later, as he is flicking through the same book, the page headings read Journey to the Centre of the Earth.
(at around 1h 20 mins) After Prof Anderson has ignited the magnesium seam in the magma pipe causing the water to pour into the pipe and generate a steam geyser, the trio can be seen lying in the bottom of the T-Rex jaw as it hurtles towards the surface at great speed. At first, despite the speed, the trio's hair (particularly Sean's) is hardly moving from the wind. The next moment, as Sean declares, "This thing's heating up." you can see that their hair is waving around wildly.
Just before the group are about to head out to sea on the raft, Trevor is shown explaining things to Sean and Hannah. When Trevor starts to explain things, he has a noticeable pimple (apparently covered with make up) then the scene goes away. But, when it returns, the pimple is gone.
When Professor Alan Kitzens is measuring up Trevor's lab with the view to closing it down, Trevor folds his arms after the two shake hands. The scene then cuts to a view of Alan as he walks towards the door, where you see Trevor in the left of the shot folding his arms again.
Sean walks across a chasm on magnetic rocks that float on a horizontal plane and bump off one another like bits of flat wood. Magnetic poles either attract or repel, so the rocks should either snap together or repel from one another, spin, then snap together. Even if large, flat magnetic rocks somehow found a natural equilibrium between their weight and magnetism, the weight of a person walking on them would destroy it.
When Trevor tries to ignite the magnesium with a flare, he claims that it's "...too wet...". Magnesium burns in water, producing magnesium oxide and hydrogen - in fact, pouring water on burning magnesium intensifies the fire; the most effective way to douse a magnesium fore is to cover it with sand or dry dirt.
Iceland lies over a volcanic plume at a place where the North American and Eurasian tectonic plates are pulling apart. The earth's crust is rather thin at that point, and any existing cave systems could not go too far down. Based on current geological science, Iceland is a very implausible location for an adventure of this depth.
The lightning bolts in the movie are highly unrealistic. Lightning can't strike the same spot as quickly as in the movie, even with a highly attractive device. Lightning only forms when a charge from the ground meets a charge from the air, so Trevor would have been hit by the first bolt when it connected with the metal rod. It is also highly unlikely that a lightning strike would have enough energy to break through the rock in the mountain.
When falling down the entrance shaft, they yell at each other. It would be impossible for them to hear each other. Skydivers in the same situation cannot communicate with each other verbally due to the wind blowing up away from their faces and would not carry over to another person. The TV show MythBusters (2003) proved verbal communication in such a situation is impossible.
When Prof. Trevor Anderson asks Hannah Ásgeirsson the temperature, a Kestrel 2500 is shown briefly with a spinning fan. In actual fact, this fan is for detecting wind speed and will not move without wind. It would be impossible for the fan to be moving in its position at that time.
In the 3-D Version, when Trevor is about to meet the T-Rex, he is walking through the red clay sandy area away from the screen. As he walks... he disappears, and the scenery remains up for a good two seconds.
In neither this movie nor Journey to the Center of the Earth (1959) nor the source Jules Verne novel, does anyone get anywhere near the literal "center" of the Earth. The title is only a metaphor, like "the sun rises in the East" - it's useful for describing what we see, but is not scientifically accurate. We know this for several reasons. 1) It is not known how long Trevor, Hannah, and Sean fall (after the talk about water and stalagmites, they continue to fall and scream, and then it fades to later), but it's definitely not a day and a half, which is how long they would need to fall to reach the actual center of the earth. After a few seconds of falling, they would reach a terminal velocity of about 120 miles per hour, so a 4000 mile fall would take about 33 hours. However, this is true only if they go to the actual center of the planet. Since the Earth's core is molten metal and rock, it's obvious that they don't travel that far. 2) The pressure at the center of Earth is believed to be 3X10 to the eleventh power pascals. The pressure at sea level is approximately 101 kPa, meaning anything from the surface would be crushed by the enormous pressure of the Earth's center, and anything from the center would collapse when exposed to the pressure of the surface. So Trevor, Sean, and Hannah would have been crushed to death, and the blue bird would not have been able to live, let alone fly. 3) At the direct center of the earth, the mass of the earth is equal in all directions. As such, the gravitational force would be equal in every direction such that it would seem to the group that there was no gravity, and they would float. 4) In the climatic scene near the end, in the magma pipe, the magma pipe extends farther down with magma rising up out of it, indicating that the actual center of the earth is still farther down.
A T-Rex skull looks like it can't float; the eye sockets and nostril would let in water. However, the T-Rex's skull is a honeycombed lattice, not solid bone, to provide both strength and flexibility. Theoretically, there could be enough air pockets to make the skull float.
Apart from the fact that the existence of the zero-gravity "magnetic field" which Sean reaches is implausible, everything seems to float around there, including the rocks and even Sean's Swiss Army knife. Although, Sean doesn't and is still subject to gravity and in danger of falling into the abyss. His head torch also drops into the chasm while he is clinging to the overturning floating rock. However; the pocket knife is metal, and is it plausible then that to an extent that the rocks are too (as they are "magnetic", and therefore likely metallic). Sean and his head torch are not, therefore would not be able to float as they are not a part of the floating magnetic field.
When racing down the mine track, all three of them have to quickly duck. When Hanna ducks she leans on the handle on the handcar and raises the other end into the wooden beams, and it does not collide - obvious CGI in use.
The goof items below may give away important plot points.
When they find the equipment left behind by an earlier expedition, Trevor remarks that it is "...state of the art... for a century ago." He's off by almost fifty years. Verne's novel was published in 1868, and he described the events as taking place in the year 1863. Anyone who was as familiar with the book as Trevor is supposed to be would know this.
(at about one hour twenty-one minutes) After the trio have been ejected by the steam geyser, they can be seen sliding down the mountain in the T-Rex jaw. The view from outside the jaw shows them moving at great speed through the vineyard while the view from within the jaw shows them moving a leisurely pace.
When Trevor is placing the final rocks on Max's grave, he is looking out to sea, but as Hannah and Sean approach him he is seen bowing towards the rock pile. When the two get there, Trevor is again still looking out to sea.
Max died alone. Some years later, Trevor, Hannah and Sean found his body and built a cairn over it; we see Trevor placing the last stone. The abrupt scene transition misleads some viewers to believe that they improbably found a cairn already standing when they arrived.