Scientists have many theories about what caused the extinction of dinosaurs. Below are thoughts on some of the most common theories:
In a word, no, but scientists can make educated guesses. The closest living relatives of the dinosaurs are crocodilians and birds, and we can look to the ways they vocalize to give us a hint.
Alligators and crocodiles use their larynxes to communicate—they’ll hiss, groan, and yes, roar (here’s a compilation of their sounds). Dinosaurs might have had larynxes, but since those don’t fossilize, it’s impossible to know for sure. Birds, meanwhile, use an organ called a syrinx, which seems to have evolved after dinosaurs. That might indicate that dinos couldn’t vocalize at all, which would be a bummer.
However, there’s also a possibility that they evolved a unique way to vocalize. For example, based on studying their skulls and inner ears, some have theorized that hadrosaurs used their crests to bellow at each other.
So, they probably didn’t roar, but bellowing can be pretty cool too, right?
This an area of common misconception. Most sedimentary rock, and the fossils contained therein cannot be dated directly with radiometric techniques, but can be dated indirectly. Here's the facts:
Casts and molds
Nothing at all. Paeleontologists chose a time where significant numbers of hard-shelled animal fossils first appeared in rocks.
It was initially believed that these were evidence of the first life on earth. As such it was decided by stratigraphers that this was a sensible point in time to create a boundary between the pre-cambrian and the newly named eon (which we are still in) - the phanerozoic, which literally means "new life".
Index fossils are used to date certain rock layers where the fossil is found. So it's usefull when you can find a certain index fossil only in a small period of time. So you can get the most precise dating for the rock layer.
Horseshoe crabs are known as a 'living fossil', the first fossils of horse shoe crabs are found 450 millions years ago.
So when you find a fossil of a horse shoe crab in a rock or sediment, you can't say anything about the age of the rock.
About 360 million years. (After the Cambrian period 550 million years ago, or "Cambrian explosion", as it is known, when most animal life began on this planet, plant life began to appear. The first plants, in the ocean, appeared 460 million years ago, and the first trees about 100 million years after that.)
Answer 2 :
Trees must not be confused with plant ! Word trees is reserved for tree ferns , gymnosperms and angiosperms , which appeared in late Paleozoic Era nearly 400 million years ago .
There are multiple methods of fossilization, but fossils generally are formed by rapid burial of organisms or traces of organisms by sediments.
Fossils occur when the organic material is filled with minerals or the cells of an organism is replaced by the minerals in water. Most of the minerals came from rocks and sands.
Here are the conditions for fossilization or permineralization:
1. Mineral-rich water like flood water or ground-erupted water.
2. Lack of oxygen - to prevent decomposition by oxygen.
3. Pressure - particularly in woods so that minerals can seep deep inside.
4. Usually occur within a few years - fossilization must occur quickly before decomposition takes place.
When a Plant or animal dies in a watery environment and is buried in sediment or soft tissues quickly decomposed leaving the hard bone or shells behind.
Well to find out what gets warmer sand or dirt you would probably need 2 plastic cups, 2 thermometers, sand, dirt and then you would have to take it outside probably in the sun or some warm area wate for about three hours and check to see what is warmer.
The answer depends on how the word 'reliable' is interpreted in the question:
(1) Is the fossil evidence 'reliable' in interpreting the history of life on Earth?
Fossil evidence IS our understanding of the history of life. Fossils on which this understanding is based include skeletons, roots, leaves, bark, chemical signatures, imprints, carbon residues, burrowing and trail marks, petrified wood, footprints, eggs, gastric stones, fecal matter, and many others, found preserved mainly in stone, but sometimes in ice. There are many ways that fossils can be formed. They include freezing, carbonization, petrification, mineral replacement, unaltered preservation,
The fossil record of life recorded in rock is full of periods of intense diversification, appearances of new lifeforms, and extinction events that affected large percentages of the biota on a worldwide scale.
(2) Are the modern methods used to determine the age of the fossil 'reliable'?Radiometric dating of rock involves the measurement of the amount of decay in radioactive elements which are present in the rock. Radioactive elements decay at unique rates, depending on the isotope. This rate of decay is known as half-lives; it is the time necessary for Â½ of the atoms to decay in a particular element. The decay follows a geometric scale, in that in the first half-life of an element, Â½ of the atoms decay, yet in the second half-life, Â½ of those remaining decay and so forth. By measuring this decay, and knowing the half life of an element, scientists can date a sample. Radiometric dating is particularly useful in dating igneous and metamorphic rock, but not so much for sedimentary rocks and fossils.
Because of geologic events such as plate tectonics and volcanism, suitable material for radiometric dating, such as volcanic tuff, solidified lava, and igneous intrusions have been found as layers on, in, and cut through layers of sedimentary rock and fossils. Intrusions are always younger than the rock body they penetrate, meaning that the sedimentary rock in which intrusions are found will be older than a radiometrically dated sample of the intrusion. Lava flows and volcanic ash which form layers in rock will be younger than the rock below and older than the rock above. The solidified intrusions and lava flows can be dated with radiometric techniques.
The radiometric dating of suitable rocks (i.e. igneous or metamorphic) in proximity to their sedimentary counterparts, therefore allows the sedimentary rock to be dated as well. Radiometric dating techniques are constantly being refined and improved with a resulting increase in accuracy and date range.
Scientific inquiry and the scientific method have contributed greatly to our lives in the fields of electronics, physics, engineering, chemistry, manufacturing, and medicine. This same scientific method is being used in genetics and Earth sciences to broaden our knowledge and understanding of Earth's history, including the origin and evolution of life.
Wegener failed to specify a possible method by which continents could move around.
Most people would not accept his theory because they thought the continents would be ploughing through solid rock.
Yes, they are.
An eon is bigger and usually contains many eras within it.
They are fine grained.
The Earth as an accreted celestial body of roughly the same size as exists today, was formed roughly 4.567 billion years ago as concluded by current (2013) scientific evidence.
Geologic Age of the Earth
Based on current scientific knowledge, the elements that form the Earth have been dated to between 4.53 to 4.58 billion years old. Not only have the oldest rocks on Earth been dated radiometrically, but so have very old, very rare meteorites and rocks brought back from the Moon. All have dated to approximately 4.5 billion years old, a fact that speaks volumes because the Moon has not undergone the tectonic and seismic changes that the Earth has.
The progressive mineral and biological strata of the Earth tell a story of a long and complex history that created the world currently occupied by man. In this chain, humankind is a relatively new and unprecedented form of life.
(see the related links)
The Biblical and Creationist Views ("Earth born old" hypothesis)
Using the records given in the Bible, scholars have estimated that the world is roughly 6,000 years old. Other religions provide varying ages based on their faiths' accounts of the Creation of heaven, Earth, and man. This is not the estimate that most of the scientific community accepts, because it requires that many of the biological and geological conditions on the Earth were created with the appearance of being much older. As documented records do not exist from the very oldest civilizations on Earth, no objective analysis of these beliefs can be made.
Rarely a fossil may appear in metamorphic or igneous rock, but the vast majority of fossil evidence presents itself in sedimentary rock. Remains or evidences of life are often preserved by being covered in sediments before decaying or being consumed by predators. The sediments may turn to rock through the process of lithification over time, leaving a record of their presence.
Limestone - by far
Gold is a naturally occurring element (element symbol Au, atomic number 79), that is created in nature e.g. during supernovae explosions of type II (see link "supernovae nucleosynthesis").
It also has been created in amounts of a several atoms by nuclear transmutation (see respective link), but it cannot be "created" or "destroyed" in the classical sense of chemistry.
On earth, gold is found mostly in solid form in veins in siliceous rocks. By alteration, it can be eroded and placed in form of powder, granules or nuggets in the riverbeds. Low concentrations of dissolved gold can also be found in the sea.Occurrence in nature
Gold occurs in nature in both its native state and in compounds. The native state of an element is its free state. It is not combined with any other element. The most common compounds of gold are the tellurides. A telluride is a compound of the element tellurium and one or more other elements.
At one time, gold was found in chunks or nuggets large enough to see. People mined gold by picking it out of streams and rivers. In fact, gold was once very common in some parts of the world. People valued it not because it was rare, but because it was so beautiful.
The abundance of gold in the Earth's crust is estimated to be about 0.005 parts per million. That makes it one of the ten rarest elements in the Earth's crust. Gold is thought to be much more common in the oceans. Some people believe as much as 70 million tons of gold are dissolved in seawater. They also think there may be another 10 billion tons on the bottom of the oceans. So far, however, no one has found a way to mine this gold.
About a quarter of the world's gold comes from South Africa. Other leading producers of the metal are the United States, Australia, Canada, China, and Russia. In the United States, about two-thirds of its gold is mined in Nevada. California, Montana, Alaska, and South Dakota also produce gold.
Increased levels of atmospheric carbon dioxide might cause global warming.
It looks like a star or possibly an asteroid. Obviously it is not a star or asteroid though.
Because they changed slowly over time :D
A paleontologist studies the history of life on Earth, mainly through the examination and study of fossils, which are evidences of ancient life that are most often found in sedimentary rock.
Paleontologists can do a number of things depending on their interests. They may strictly do lab work--cleaning, identifying, sorting bones and fossils; chemically analyzing material, reassembling fossil structures, preparing exhibits. They can also do field work involving the search and discovery of ancient life. They also prepare scientific papers and come up with new scientific theories based on new or previously published information. Finally, some paleontologists can make a living with a career in teaching.
There is currently no evidence of grass in the Triassic Period.
Until recently it was thought that grass evolved around 55 million years ago but recent findings suggesting that grass became common 66-65 million years ago comes from the very end of the Cretaceous Period. Some dinosaur coprolites show material that appears to have been grass.
It is now believed that Grass's evolved sometime in the late Cretaceous and became widespread just prior to the K-T Extinction Event.
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