Why are we a certain number of years old when all of the atoms in our body are ~14billion years old? When we talk about age, we talk about when the structure was formed, not the materials. When people say a lava rock is 5 million years old, they mean magma came out of a volcano and cooled on Earth’s surface in this structure 5 million years ago.
Why do you, u/kepler1 say that you are <some number> of years old, if (almost) all the material you are made of has the same initial source as everything else on the Earth?
Not all rock forms the same way and not all rock forms at the same time. E.g. sedimentary rock forms from fine stuff that accumulated over centuries and got crushed into rock. Volcanic rock also formed from lava at some point in history. There were some events in the Earth history that caused this rock to be take that particular form.
Dating all rocks to the year of the Earth would be the same as dating a human to the year of the Earth because everything that makes up a human comes from the same source.
We date rocks based on when they were formed just like we date humans based on when they were formed.
Because molecules morph into other molecules under the right conditions. Exposure, temperature, and pressure can all change one thing into another. Even forms of the same element can change with these conditions due to how the molecules are bound together. Graphite and diamonds are both carbon fused together differently.
Because not all rock is from the same initial source, unless you go back to before it was rock. Limestone, for example, is made of shells which are formed from dissolved calcium salts in water. Stone can be dissolved and re-deposited, transformed by extreme heat and pressure etc.
it’s kinda like baking a cake from the same ingredients but at different times. yeah, all the material came from the same place originally, but rocks form and change over time through different processes. so when geologists say a rock is X million years old, they mean that specific rock structure solidified or changed at that time, not that the atoms in it are that young.
It might be made from old ingredients, but that doesn’t mean it’s the same ‘age’. A cake is ‘newer’ than the flour used to bake it, for example. Rock can be made from minerals in water depositing over millions of years, or from hardened lava from a volcano erupting in 5000 BC.
You are correct in that the raw materials to make rocks have been reused and recycled since the Earth began. When geologists talk about the age of a rock, they talk about when that rock was formed.
For example, when a volcano erupts, the lava cools and forms new rock. That lava was created by melting older rocks and will contain small cystals leftover from those older rocks, but the age of the new rock matches when the volcano erupted and the lava solidifed
Sedimentary rocks are formed when small pieces of older rocks are transported and later cemented together. The age of a sedimentary rock will be the cementation age, but the individual grains may be much, much older.
Metamorphic rocks are formed when older rocks are heated and squashed over time. The age of those rocks will be the solidifying or cementing ages above, but they will also talk about when the rock was altered by metamorphism, which is always a younger age.
When you bake a cake on Saturday, how old would you say the cake is on Sunday? As old as the flour? As old as the eggs, the butter, or the sugar? No, right? You’d say it was a day old, because that’s how long ago you baked those ingredients into the cake.
Rocks are formed and destroyed all the time. Their “ingredients” remain, and most of those ingredients were indeed here when the Earth first formed. But the age of any given rock or geological formation is the age that it was formed – not the age of its ingredients.
How are rocks (or how is rock) formed? Basically three ways. One is molten lava that cools down, for instance after a volcanic eruption. The lava wasn’t rock before, but becomes rock when it solidifies. The age of this volcanic rock refers to how long ago this happend. Another way is sedimentation. Basically mineral particles in rivers, lakes, seas etc. drop down to the bottom and settle into place, and as layers upon layers of sediment are deposited, they get compressed, stuck together and turned into rock. So the age of this sedimentary rock refers to when that process happened. Finally, there is metamorphic rock. This type of rock forms when existing rock gets transformed, for instance by heat or pressure (but not so much that it melts – then we’d be back to volcanic rock). This transformation alters the structure of the rock in such a way that we consider it a new rock, and we measure the age of this rock relative to when the transformation happened.
Rocks form in a very large amount of ways, and earth is composed of many many different types of materials that cause different rocks to form. Rocks are constantly forming all the time and it’s important to know how and when they form to better understand things like geology and chemistry.
Some are made when a certain common substance packs tightly together (sedimentary), some are made when they start out as a liquid substance then cool when a volcano spits them out (igneous) and some start out as rocks of other kinds, get pushed down and heat up which forms entirely new rocks all together (metamorphosis)
Some rocks aren’t even made of minerals found on earth when it originally formed. Some are made by materials created by life forms (limestone), or stuff from outer space that crashed into earth (asteroids).
By looking at things around the rock, what layers are underneath it and on top, if there’s evidence of volcanoes, and what type of structure and minerals the rock is made of, we can make educated guesses based on when they formed. We can also test them and they give us information to help better identify when they formed.
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Why are we a certain number of years old when all of the atoms in our body are ~14billion years old? When we talk about age, we talk about when the structure was formed, not the materials. When people say a lava rock is 5 million years old, they mean magma came out of a volcano and cooled on Earth’s surface in this structure 5 million years ago.
They’re referring to when that specific body of rock was formed after years of sediment and mineral buildup/compression.
Why do you, u/kepler1 say that you are <some number> of years old, if (almost) all the material you are made of has the same initial source as everything else on the Earth?
Not all rock forms the same way and not all rock forms at the same time. E.g. sedimentary rock forms from fine stuff that accumulated over centuries and got crushed into rock. Volcanic rock also formed from lava at some point in history. There were some events in the Earth history that caused this rock to be take that particular form.
Dating all rocks to the year of the Earth would be the same as dating a human to the year of the Earth because everything that makes up a human comes from the same source.
We date rocks based on when they were formed just like we date humans based on when they were formed.
Because molecules morph into other molecules under the right conditions. Exposure, temperature, and pressure can all change one thing into another. Even forms of the same element can change with these conditions due to how the molecules are bound together. Graphite and diamonds are both carbon fused together differently.
Because not all rock is from the same initial source, unless you go back to before it was rock. Limestone, for example, is made of shells which are formed from dissolved calcium salts in water. Stone can be dissolved and re-deposited, transformed by extreme heat and pressure etc.
it’s kinda like baking a cake from the same ingredients but at different times. yeah, all the material came from the same place originally, but rocks form and change over time through different processes. so when geologists say a rock is X million years old, they mean that specific rock structure solidified or changed at that time, not that the atoms in it are that young.
It might be made from old ingredients, but that doesn’t mean it’s the same ‘age’. A cake is ‘newer’ than the flour used to bake it, for example. Rock can be made from minerals in water depositing over millions of years, or from hardened lava from a volcano erupting in 5000 BC.
You are correct in that the raw materials to make rocks have been reused and recycled since the Earth began. When geologists talk about the age of a rock, they talk about when that rock was formed.
For example, when a volcano erupts, the lava cools and forms new rock. That lava was created by melting older rocks and will contain small cystals leftover from those older rocks, but the age of the new rock matches when the volcano erupted and the lava solidifed
Sedimentary rocks are formed when small pieces of older rocks are transported and later cemented together. The age of a sedimentary rock will be the cementation age, but the individual grains may be much, much older.
Metamorphic rocks are formed when older rocks are heated and squashed over time. The age of those rocks will be the solidifying or cementing ages above, but they will also talk about when the rock was altered by metamorphism, which is always a younger age.
When you bake a cake on Saturday, how old would you say the cake is on Sunday? As old as the flour? As old as the eggs, the butter, or the sugar? No, right? You’d say it was a day old, because that’s how long ago you baked those ingredients into the cake.
Rocks are formed and destroyed all the time. Their “ingredients” remain, and most of those ingredients were indeed here when the Earth first formed. But the age of any given rock or geological formation is the age that it was formed – not the age of its ingredients.
How are rocks (or how is rock) formed? Basically three ways. One is molten lava that cools down, for instance after a volcanic eruption. The lava wasn’t rock before, but becomes rock when it solidifies. The age of this volcanic rock refers to how long ago this happend. Another way is sedimentation. Basically mineral particles in rivers, lakes, seas etc. drop down to the bottom and settle into place, and as layers upon layers of sediment are deposited, they get compressed, stuck together and turned into rock. So the age of this sedimentary rock refers to when that process happened. Finally, there is metamorphic rock. This type of rock forms when existing rock gets transformed, for instance by heat or pressure (but not so much that it melts – then we’d be back to volcanic rock). This transformation alters the structure of the rock in such a way that we consider it a new rock, and we measure the age of this rock relative to when the transformation happened.
Because rocks are formed, altered, destroyed, recycled etc all the time (on a geological timescale)
They are specifying when that rock formed.
Rocks form in a very large amount of ways, and earth is composed of many many different types of materials that cause different rocks to form. Rocks are constantly forming all the time and it’s important to know how and when they form to better understand things like geology and chemistry.
Some are made when a certain common substance packs tightly together (sedimentary), some are made when they start out as a liquid substance then cool when a volcano spits them out (igneous) and some start out as rocks of other kinds, get pushed down and heat up which forms entirely new rocks all together (metamorphosis)
Some rocks aren’t even made of minerals found on earth when it originally formed. Some are made by materials created by life forms (limestone), or stuff from outer space that crashed into earth (asteroids).
By looking at things around the rock, what layers are underneath it and on top, if there’s evidence of volcanoes, and what type of structure and minerals the rock is made of, we can make educated guesses based on when they formed. We can also test them and they give us information to help better identify when they formed.