2007-01-01 06:17:20 · 4 answers · asked by Sarah M 1 in Science & Mathematics ➔ Earth Sciences & Geology
Direct dating of the sea floor must involve radiometric dating of the basalt rock lying beneath the sediments; typically Potassium-Argon or Uranium-Lead techniques.
The seafloor gets progressively older away from the ocean ridges where it forms, and as the magnetic field of the Earth periodically changes polarity, the magnetism preserved in these basalt rocks indicates whether a "normal" or "reversed" field was operating when they solidified. There are thus "stripes" of normal and reversed magnetism either side of the ridges. These won't tell you how old the rock is, but sequences of banding can be compared rather like tree rings.
The sediment covering the basalt crust can't normally be directly dated, and of course it is still forming, so the the date of the immediate seafloor surface over much of the world is..today!!
Older sediments can be dated in relative terms by the fossils they contain, and since much of the seafloor "ooze" is almost completely microscopic fossils, there is plenty to work with. You can then build up a dating framework with the fossils and the radiometric dates: if a particular fossil is found in rocks immediately covering basalt dated at 15 million years, that is the youngest possible age for them. If similar fossils are then found elsewhere, the basalt beneath is probably older than about 15 m.y. - but of course if that particular species actually lived between 16 m.y. and 14 m.y ago, there is a band of error. Also, you don't know how much older than the fossil that rock is, only that it can't be younger.
Organic material in the sediments can be dated by Radiocarbon techniques, but Carbon 14 has a very short half-life geologically, about 6,400 years, so any sediments older than about 40,000 years have too little C14 left to allow dating.
2007-01-02 23:21:04 · answer #1 · answered by Paul FB 3 · 1⤊ 0⤋
Various methods, sediment piles up on the bottom of the see and forms layers, these can be used to determine the age of different depths. Events like large volcanic eruptions cause layers that stand out due to changed composition of the layer.
The rock itself can be aged using various radiological dating techniques
2007-01-01 14:25:36 · answer #2 · answered by Gordon B 7 · 0⤊ 0⤋
Carbon dating
2007-01-02 11:49:29 · answer #3 · answered by Vulture38 6 · 0⤊ 0⤋
by the magnetic signature of the rock. do your own homework !!!!
2007-01-01 14:22:14 · answer #4 · answered by cereal killer 5 · 0⤊ 0⤋