In my opinion you commit an error.
These small rocky worlds are thought to have been born in a disc of dust and gas that surrounded the Sun. As time went by, the dust grains snowballed into larger and larger rocks and boulders. About 4. The terrestrial planets we see today are the survivors of a prolonged, chaotic period of colossal impacts which left their surface imprints in the form of giant basins and craters. How can we piece together a planet's history since its formation? On Earth, the geological timeline is quite easy to determine, since we can analyse the rocks and minerals in laboratories.
If you had 1 gram of pure radioactive nuclei with a half-life of years, then after years you would have.
However, the material does not disappear. Instead, the radioactive atoms are replaced with their decay products. Sometimes the radioactive atoms are called parents and the decay products are called daughter elements. In this way, radioactive elements with half-lives we have determined can provide accurate nuclear clocks. By comparing how much of a radioactive parent element is left in a rock to how much of its daughter products have accumulated, we can learn how long the decay process has been going on and hence how long ago the rock formed.
Table 1 summarizes the decay reactions used most often to date lunar and terrestrial rocks. When astronauts first flew to the Moon, one of their most important tasks was to bring back lunar rocks for radioactive age-dating. Until then, astronomers and geologists had no reliable way to measure the age of the lunar surface. Counting craters had let us calculate relative ages for example, the heavily cratered lunar highlands were older than the dark lava plainsbut scientists could not measure the actual age in years.
Only inwhen the first Apollo samples were dated, did we learn that the Moon is an ancient, geologically dead world. Using such dating techniques, we have been able to determine the ages of both Earth and the Moon: each was formed about 4.
We should also note that the decay of radioactive nuclei generally releases energy in the form of heat. Although the energy from a single nucleus is not very large in human termsthe enormous numbers of radioactive nuclei in a planet or moon especially early in its existence can be a significant source of internal energy for that world.
The ages of the surfaces of objects in the solar system can be estimated by counting craters: on a given world, a more heavily cratered region will generally be older than one that is less cratered. We can also use samples of rocks with radioactive elements in them to obtain the time since the layer in which the rock formed last solidified.
The half-life of a radioactive element is the time it takes for half the sample to decay; we determine how many half-lives have passed by how much of a sample remains the radioactive element and how much has become the decay product. In this way, we have estimated the age of the Moon and Earth to be roughly 4.
Skip to main content. Login Register. We have rocks from the Moon brought backmeteorites, and rocks that we know came from Mars. We can then use radioactive age dating in order to date the ages of the surfaces when the rocks first formed, i. We also have meteorites from asteroids and can date them, too.
These are the surfaces that we can get absolute ages for. For the others, one can only use relative age dating such as counting craters in order to estimate the age of the surface and the history of the surface. The biggest assumption is that, to first order, the number of asteroids and comets hitting the Earth and the Moon was the same as for Mercury, Venus, and Mars.
There is a lot of evidence that this is true. The bottom line is that the more craters one sees, the older the surface is. This can be interpreted in two ways: why it is important to know the age of a planet or how is age dating important in determining the age of a planet? Based on our study of meteorites and rocks from the Moon, as well as modeling the formation of planets, it is believed pretty much well-established that all of the objects in the Solar System formed very quickly about 4.
When we age date a planet, we are actually just dating the age of the surface, not the whole planet.
Determining the age of surfaces on Mars
We can get absolute ages only if we have rocks from that surface. For others, all we are doing is getting a relative age, using things like the formation of craters and other features on a surface. By studying other planets, we are learning more about our own planet. The effects of impacts and how they might affect us here on Earth, global climate change Venus vs.
Earth and what could happen to Earth in an extreme case, etc. From Wikipedia, radioactive decay is the process in which an unstable atomic nucleus spontaneously loses energy by emitting ionizing particles and radiation. This decay, or loss of energy, results in an atom element of one type, called the parent nuclide transforming to an atom of a different type another element or another isotope of the same elementnamed the daughter nuclide. For example: a carbon atom the "parent" emits radiation and transforms to a nitrogen atom the "daughter".
It is impossible to predict when a given atom will decay, but given a large number of similar atoms, the decay rate on average is predictable.
For example, one could make a map of the surface, color-coding it such that each radiometric dating until we can study rocks from their surfaces in a laboratory. numbers of craters, one asks "what use can we make of craters to determine We can roughly divide the history of crater formation into three periods, from.
We have no idea how much older thing B is, we just know that it's older. That's why geologic time is usually diagramed in tall columnar diagrams like this. Just like a stack of sedimentary rocks, time is recorded in horizontal layers, with the oldest layer on the bottom, superposed by ever-younger layers, until you get to the most recent stuff on the tippy top.
On Earth, we have a very powerful method of relative age dating: fossil assemblages. Paleontologists have examined layered sequences of fossil-bearing rocks all over the world, and noted where in those sequences certain fossils appear and disappear.
FAQ - Radioactive Age-Dating
When you find the same fossils in rocks far away, you know that the sediments those rocks must have been laid down at the same time.
The more fossils you find at a location, the more you can fine-tune the relative age of this layer versus that layer. Of course, this only works for rocks that contain abundant fossils. Conveniently, the vast majority of rocks exposed on the surface of Earth are less than a few hundred million years old, which corresponds to the time when there was abundant multicellular life here.
Look closely at the Geologic Time Scale chartand you might notice that the first three columns don't even go back million years.
How do we know the age of the surfaces we see on planets and moons? to rock samples from the Moon to establish a geological chronology for the Moon. directly (see the chapter on Cosmic Samples and the Origin of the Solar System). Scientists measure the age of rocks using the properties of natural radioactivity. We use a variety of laboratory techniques to figure out absolute age-dating method that works from orbit, and although scientists are the major and minor geologic time periods we use to split up the history Relative-age time periods are what make up the Geologic Time Scale. .. Venus' Lower Clouds. It's difficult for scientists to figure out the geological history of Venus. The environment is too harsh for a rover to go there. It is even more difficult.
That last, pink Precambrian column, with its sparse list of epochal names, covers the first four billion years of Earth's history, more than three quarters of Earth's existence. Most Earth geologists don't talk about that much.
Paleontologists have used major appearances and disappearances of different kinds of fossils on Earth to divide Earth's history -- at least the part of it for which there are lots of fossils -- into lots of eras and periods and epochs. When you talk about something happening in the Precambrian or the Cenozoic or the Silurian or Eocene, you are talking about something that happened when a certain kind of fossil life was present.
Major boundaries in Earth's time scale happen when there were major extinction events that wiped certain kinds of fossils out of the fossil record.
The geological history of Mars has been divided into three main periods, each ago, but scientists think that the planet endured an extremely high rate of impacts. Eventually, the water vapour in the atmosphere would have condensed into a Many of the valley networks on Mars date from this period, and lakes seem to. The geology of solar terrestrial planets mainly deals with the geological aspects of the four Three of the four solar terrestrial planets (Venus, Earth, and Mars) have scientists have a first-order understanding of the geology and history of the the degree of degradation gives a rough indication of the crater's relative age. For the others, one can only use relative age dating (such as counting craters) in order to estimate the age of the surface and the history of the surface. and comets hitting the Earth and the Moon was the same as for Mercury, Venus, and Mars. By studying other planets, we are learning more about our own planet.
This is called the chronostratigraphic time scale -- that is, the division of time the "chrono-" part according to the relative position in the rock record that's "stratigraphy". The science of paleontology, and its use for relative age dating, was well-established before the science of isotopic age-dating was developed. Nowadays, age-dating of rocks has established pretty precise numbers for the absolute ages of the boundaries between fossil assemblages, but there's still uncertainty in those numbers, even for Earth.
In fact, I have sitting in front of me on my desk a two-volume work on The Geologic Time Scalefully pages devoted to an eight-year effort to fine-tune the correlation between the relative time scale and the absolute time scale. The Geologic Time Scale is not light reading, but I think that every Earth or space scientist should have a copy in his or her library -- and make that the latest edition. In the time since the previous geologic time scale was published inmost of the boundaries between Earth's various geologic ages have shifted by a million years or so, and one of them the Carnian-Norian boundary within the late Triassic epoch has shifted by 12 million years.
Two basic types of dating are possible: absolute and relative. Using the techniques of statistical celestial mechanics, first developed by E. J. Opik . origin and the broad outline of the history of volcanism on Venus could be ascertained Dating techniques are essential to geologic studies of planets and satellites in that. Venus is a planet with striking geology. Of all the other planets in the Solar System, it is the one Much speculation about the geological history of Venus continues today. . implying that the surface of the entire planet is roughly the same age, or at . Gravitational studies suggest that Venus differs from Earth in lacking an. Scientists find the age of the Earth by using radiometric dating of Many great thinkers throughout history have tried to figure out Earth's age.
With this kind of uncertainty, Felix Gradstein, editor of the Geologic Time Scale, suggests that we should stick with relative age terms when describing when things happened in Earth's history emphasis mine :. For clarity and precision in international communication, the rock record of Earth's history is subdivided into a "chronostratigraphic" scale of standardized global stratigraphic units, such as "Devonian", "Miocene", " Zigzagiceras zigzag ammonite zone", or "polarity Chron C25r".
Unlike the continuous ticking clock of the "chronometric" scale measured in years before the year ADthe chronostratigraphic scale is based on relative time units in which global reference points at boundary stratotypes define the limits of the main formalized units, such as "Permian". The chronostratigraphic scale is an agreed convention, whereas its calibration to linear time is a matter for discovery or estimation. Got that? We can all agree to the extent that scientists agree on anything to the fossil-derived scale, but its correspondence to numbers is a "calibration" process, and we must either make new discoveries to improve that calibration, or estimate as best we can based on the data we have already.
To show you how this calibration changes with time, here's a graphic developed from the previous version of The Geologic Time Scalecomparing the absolute ages of the beginning and end of the various periods of the Paleozoic era between and I tip my hat to Chuck Magee for the pointer to this graphic. Fossils give us this global chronostratigraphic time scale on Earth.
On other solid-surfaced worlds -- which I'll call "planets" for brevity, even though I'm including moons and asteroids -- we haven't yet found a single fossil. Something else must serve to establish a relative time sequence.Venus's Recent Geologic History
That something else is impact craters. Earth is an unusual planet in that it doesn't have very many impact craters -- they've mostly been obliterated by active geology. Venus, Io, Europa, Titan, and Triton have a similar problem. On almost all the other solid-surfaced planets in the solar system, impact craters are everywhere. The Moon, in particular, is saturated with them.
We use craters to establish relative age dates in two ways. If an impact event was large enough, its effects were global in reach.
For example, the Imbrium impact basin on the Moon spread ejecta all over the place. Any surface that has Imbrium ejecta lying on top of it is older than Imbrium. Any craters or lava flows that happened inside the Imbrium basin or on top of Imbrium ejecta are younger than Imbrium.
Imbrium is therefore a stratigraphic marker -- something we can use to divide the chronostratigraphic history of the Moon.
How do scientists use relative dating to study the geologic history of venus
The other way we use craters to age-date surfaces is simply to count the craters. At its simplest, surfaces with more craters have been exposed to space for longer, so are older, than surfaces with fewer craters. Of course the real world is never quite so simple. There are several different ways to destroy smaller craters while preserving larger craters, for example.
Despite problems, the method works really, really well. Most often, the events that we are age-dating on planets are related to impacts or volcanism.
Volcanoes can spew out large lava deposits that cover up old cratered surfaces, obliterating the cratering record and resetting the crater-age clock.